Effect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization

Effect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization Ninghui Xie, Sean Michael Schaeffer, Tingting An, Yingde Xu, Shuangyi Li, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-341230/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The labile organic carbon (C) pool plays a vital role in soil biogeochemical transformation and can be used as a sensitive indicator of the response of soil quality to agricultural practice. However, little is known about how residue type and soil fertilization affect the incorporation of residue C into labile organic C pools. A 360-day laboratory incubation was conducted with the addition of 13 C-labeled maize residues (root, stem and leaf) to unfertilized and organic-fertilized soils. A greater contribution of residue C to extractable organic C (EOC, 7.2%) was observed in the unfertilized soil than that in the organic-fertilized soil (6.0%). The contribution of residue C to microbial biomass C (MBC) was 20%-50% in the organic-fertilized soil, but only 10%-30% in the unfertilized soil. This suggests that, in organic-fertilized soil, there is accelerated transformation of residue C into microbial biomass and a higher capacity for residue C stabilization through greater, or more efficient anabolism. Moreover, the distribution of leaf C into MBC was higher than that from root and stem in the unfertilized soil, whereas more root C entered to EOC and MBC than from stem and leaf in the organic-fertilized soil. This shows that maize root can also be involved in microbial assimilation, but it depends on the initial soil nutrition. Overall, these findings deepen our understanding of the mechanisms of microbe-mediated C transformation processes, and provide relevant insights into the capture and incorporation of plant residue C into labile organic C pools driven by residue type and soil fertilization. Geochemistry maize residue soil fertilization 13C-labeling technique extractable organic carbon microbial biomass carbon Figures Figure 1 Figure 2 Introduction Soil organic carbon (SOC) sequestration is critical for agriculture and the environment, particularly in soil health and food security (Lal, 2004 ). SOC stocks are governed by the balance between carbon (C) input and output, and strongly affected by soil management practices (Paustian et al. 2000 ). Adoption of plant residue retention methods are essential to maintain, or improve SOC content and the sustainability of agricultural systems (Lal 2004 ; Diacono et al. 2010). However, SOC dynamics induced by plant residue retention generally occurs slowly since the total SOC pool is too large to be affected in the short-term (Salinas-Garcia et al. 1997 ; Ding et al. 2012 ). In this context, SOC fractions with relatively higher turnover rates and/or reactivity can be used to quantify the effect of agricultural management on soil quality (Silveira et al. 2008 ). Specifically, soluble organic C and microbial biomass C (MBC) fractions respond more quickly to soil management activities than other C pools (Nieder et al. 2008 ; Lehmann and Kleber 2015 ). Plant residues provide available substrate for soil microorganisms (Shahbaz et al. 2017a ), and in turn play an important role in microbe-mediated biogeochemical processes (Ge et al. 2015 ; Haubensak et al. 2002 ). Plant residue can be preferentially utilized by microorganisms for biomass production during microbial growth processes (Liang et al., 2017 ). Microorganisms solubilize plant-derived C through depolymerization by extracellular enzymes, and any net increase in the soluble C fraction is driven by microbial death, exudation, or a decrease in microbial assimilation (Burns et al. 2013 ). Generally, the dynamics of microbial utilization of residue C and stabilization, for example, relative abundances of soluble organic C and MBC, are mainly mediated by plant residue quality (Chen et al. 2009 ; Prescott 2010 ; Liang et al., 2017 ). In the traditional view, root residue is relatively recalcitrant, and has a slower decomposition rate, thus more root C is incorporated into the stable SOC fractions than that from stem and leaf residues (Lian et al. 2016 ; Johnson et al. 2014 ). However, a prevailing counter hypothesis proposes that labile C compounds can contribute more to long-term soil C stability than highly recalcitrant chemical compounds such as lignin (Amelung et al., 2008 ; Schmidt et al., 2011 ; Lehmann and Kleber 2015 ). This is because above-ground residues (e.g. stem and leaf residues) contain more easily degradable C, which plays a significant role in labile organic C accumulation, and subsequently, may contribute more to SOC sequestration due to high microbial utilization efficiency (Don and Kalbitz 2005 ; Cotrufo et al. 2013 , 2015 ). These new theories challenge our understanding of the mechanisms of how root vs . aboveground residues is involved in SOC formation. Therefore, given the important role of labile C in the SOC accumulation, it is necessary to strengthen our knowledge of the impacts of plant residue type on the microbial assimilation of exogenous C and the dynamics of soil labile C, i.e., soluble organic C and MBC. Soil fertilization and total SOC are important factors controlling microbial assimilation of plant residue (Wang et al. 2014 ; Zhu et al. 2016; Marschner et al. 2001 ). The dynamics and distribution of residue C in soil depends upon soil fertility under long-term soil fertilization regimes because more residue C tends to accumulate in MBC in low fertility soil compared with high fertility soil (An et al. 2015a ). However, the combined applications of plant residues (leaf, stems and roots) in soils may differentially affect proportional labile organic C accumulation, resulting in differences in residue C accumulation in the total SOC pool of the soils with different levels of SOC (Lian et al. 2016 ). Because microbial competition for residue C depends upon initial soil properties (An et al. 2015a ), the application of organic fertilizers, which enhance soil fertility (Macci et al. 2013 ; Jin et al. 2018 ), is expected to affect microbial utilization of plant residues. In general, the addition of residue C to soil enhances soil labile organic pools (An et al. 2015a ), but the additions of different quality residues in soils with different levels of SOC and nutrients determine its accumulation (Singh et al. 2007 ; Fang et al. 2018 ). The effect of soil fertilization on the incorporation of different types of maize residues into labile C pools has received far less attention. The objectives of our research were: (1) to quantify the contribution of different types of maize residue to soluble organic C, measured as extractable organic C (EOC), and MBC and (2) to determine the differences in distribution and utilization of residue C in long-term soil fertilization among residue types. We added the 13 C-labeled maize residues (leaf, stem and root) to unfertilized and organic-fertilized soils and incubated the soils for 360 days. The percentages of different residue C in EOC and MBC fractions were determined. The incubation study was designed to test the following hypotheses: (1) plant residue addition would increase the labile organic C, with its magnitude depending on the residue types, i.e., more aboveground residue C would be incorporated in labile organic C than root residue C; (2) soil fertilization would regulate the distribution of plant residue C in EOC and MBC, and the greater distribution of residue C in labile organic C would be in unfertilized soil because of C deficiency than organic-fertilized soil. Materials And Methods Experimental site and soil sampling Soil samples were collected from a long-term fertilization experiment station (41°49’N, 123°34’E) that was established in 1987 at Shenyang Agricultural University, Liaoning, China. This region is characterized by a typical continental monsoon climate, with annual mean temperature of 7.9 o C and annual mean precipitation of 705 mm. The soil type is Brown Earth according to the Chinese Soil Taxonomy (a Hapli-Udic Alfisol according to the USDA Taxonomy, Soil Survey Staff, 1999 ). The cropping system is monoculture maize which is sown in early May and harvested in early October each year. A detailed description of this site was given by An et al. ( 2015b ). Field plots with two fertility levels were selected for this study: (1) no fertilizer application (unfertilized soil); (2) application of composted swine manure (270 kg N ha y − 1 ) for more than 27 years (organic-fertilized soil). The compost contained 150 g kg − 1 total organic C; 10 g kg − 1 total N; 10 g kg − 1 P 2 O 5 and 4 g kg − 1 K 2 O on a dry weight basis (An et al. 2015a ). In each plot, a total of five samples were randomly collected, and then fully mixed to form one composite soil sample to represent each experimental plot. Soil samples (0–20 cm depth) were collected in November, 2014, and all visible crop roots and debris were removed, then all the soil samples were sieved (2mm) and air-dried for the subsequent incubation experiment. The main soil properties of the soil samples are shown in Table 1 . Table 1 Basic characteristics of soil samples in long-term fertilization of soils (in 2014) Soil fertilization Total soil organic carbon (g kg − 1 ) δ 13 C (‰) Total nitrogen (N, g kg − 1 ) Total phosphorus (P, g kg − 1 ) C/N C/P Clay (%) pH (H 2 O) Microbial biomass carbon (mg kg − 1 ) Unfertilized 10.10 ± 0.15 -17.88 ± 0.15 1.10 ± 0.06 4.92 ± 0.24 8.91 ± 0.13 2.05 ± 0.63 * 17.30 ± 0.13 6.11 ± 0.23 117.69 ± 3.25 Organic-fertilized 17.80 ± 0.16 * -19.45 ± 0.17 * 2.20 ± 0.02 * 22.77 ± 2.48 * 8.10 ± 0.11 0.78 ± 0.06 18.94 ± 0.14 6.31 ± 0.27 163.54 ± 5.23 * a Unfertilized: long-term no fertilization soil; Organic-fertilized: long-term organic manure fertilization soil. b Stars show the significant differences ( P < 0.05) between soil fertilizations at the same indicator. Preparation of 13 C-labeled maize residue Root, stem and leaf residue were obtained from fully matured maize plants that had been pulse-labeled with 13 CO 2 (98 atom %) for six times across the whole growth stages in 2014 (An et al. 2015b ). The aboveground plant was cut at the root base and then stem and leaf residues were carefully collected. The main and lateral roots were gently separated from soil and then washed off the adhering soil with tap water. All the sampled residues were oven-dried at 70 ℃ for 12 h. Five plants (root, stem, and leaf, respectively) were randomly selected from all the labeling maize plants and then chopped 5 mm segments. After that, the residues were selected by the quartering methods and then ground into less than 0.5-mm segments. Root residue contained 400 g kg − 1 total organic C, 12.6 g kg − 1 total N, 394‰ δ 13 C value, and C/N ratio of 32. Stem residue contained 440 g kg − 1 total organic C, 14.5 g kg − 1 total N, 696‰ δ 13 C value, and C/N ratio of 30. Leaf residue contained 421 g kg − 1 total organic C, 12.7 g kg − 1 total N, 662‰ δ 13 C value, and C/N ratio of 33. Incubation experiment Air-dried soil sample (120 g) was weighted into 500 ml incubation vessels. Soil was then pre-incubated at 35% of its water holding capacity (WHC) at 25 ºC for 7 days, because sieving affects the availability of soil organic matter (SOM) for soil microorganisms (An et al. 2015a ). The pre-incubated soil samples were amended with root, stem and leaf residues (1% of oven-dried soil weight), respectively. No amendment was applied in the control treatment. The added residues were thoroughly mixed with incubated soil. The glass vessels were sealed with parafilm, and several tiny holes were drilled in the parafilm in order to allow gas going through while retarding soil water evaporation (Wang et al. 2014 ). Soil samples were incubated at 25℃ at 60% WHC for 360 days under darkness. Periodically, the vessels were weighed, and the soil water content was maintained at the original soil moisture level throughout the incubation period by supplementation with distilled water. Three replicates of each treatment were randomly and destructively sampled on the 1st, 7th, 28th, 56th, 180th and 360th day after incubation. A part of the sample was stored at 4 ℃ for EOC and MBC analysis. While the other part was air-dried, ground through 0.15 mm sieve and analyzed for SOC content and δ 13 C value. MBC and EOC determination MBC was determined using chloroform-fumigation extraction (Vance et al. 1987 ). Briefly, fresh soil samples (equivalent to 10 g oven-dried soil) were fumigated with purified CHCl 3 for 24 h in the dark at 25 o C. After fumigation, the soil samples were extracted with 0.5 M K 2 SO 4 at 1:4 soil: solution ratio. An equivalent amount of non-fumigated soil was also extracted when fumigation commenced. The organic C of the non-fumigated extract was the EOC (Schaeffer et al. 2013 ). The organic C content of soil extract was determined with the Total Organic Carbon Analyzer (Elementar High TOC II, Germany). MBC was calculated as the difference in organic C content between fumigated and non-fumigated soil extracts with a correction factor ( k EC ) of 0.45 (Wu et al. 1990 ). All K 2 SO 4 -extract aliquots (20 ml) were freeze-dried for the determination of 13 C abundances. Isotopic C analysis and calculation Analyses of the organic C contents and δ 13 C values in soil were conducted in an elemental analyzer (Elementar Vario PYRO cube, Germany) coupled to an isotope ratio mass spectrometer (IsoPrime 100 Isotope Ratio Mass Spectrometer, Germany). δ 13 C values of K 2 SO 4 extract samples were also determined in the same way. The δ 13 C value was expressed in parts per mil (‰) relative to the international standard Pee Dee Belemnite (PDB) (Werner and Brand 2001 ). The δ 13 C value of MBC (δ 13 C MBC , ‰) was calculated as follows: where C F and δ 13 C F are the total organic C content (mg kg soil − 1 ) and δ 13 C value (‰) in the fumigated extracts, respectively, and C NF and δ 13 C NF are the total organic C content (mg kg soil − 1 ) and δ 13 C value (‰) in the non-fumigated extracts, respectively. The percentage ( f , %) of maize residue C in MBC and EOC was calculated according to De Troyer et al. (2011): where δ 13 C sample is the δ 13 C value (‰) of C pool in soil sample treated with maize residue, δ 13 C control is the δ 13 C value (‰) of C pool do the corresponding soil sample without maize residue addition and δ 13 C residue0 is the δ 13 C value of the applied maize residue. The content of C pool derived from residue C (C residue ) was calculated with the following equation (Blaud et al. 2012 ): where C sample is the total content of C pool in EOC and MBC. Repeated measures analysis was performed for all data over time, using a linear mixed model consisting of fixed effects of soil fertilization (unfertilized and organic-fertilized soil), plant residue types (maize root, stem and leaf), and time and their associated interaction, and random effects of replicates and replicates by time. All repeated measurements satisfy the assumption of sphericity. To allow for correlation between repeated measures on the same treatment, a first-order antedependence correlation model was assumed for the residuals within a plot (Fang et al., 2018 ). Differences between soil fertilizations were assessed by paired T-test. All statistical analyses were performed with IBM SPSS 19.0 (IBM, USA) software package with significant differences at P < 0.05 level. Graphs were drawn using Origin 8 (Origin Lab, USA). Results Contribution of maize residue C to EOC Soil fertilization and residue type significantly affected ( P < 0.05) the contents of EOC (Table 2 ). EOC decreased from 241 mg kg − 1 soil to 138 mg kg − 1 soil (Fig. 1 a and b) during the incubation time. And it was 1–2 times higher in the organic-fertilized soil than that in the unfertilized soil treated with residues. The content of EOC in the unfertilized soil treated with root residue was lower than those treated with stem and leaf residues during the whole incubation. However, the opposite trend was observed in the organic-fertilized soil treated with residues after 56 days. At the end of incubation (360th day), the EOC content in the organic-fertilized soil added with root residue was about 30% higher than those of stem and leaf residues. Table 2 Statistical significance ( P values) of the fixed terms of soil fertilization (F; unfertilized soil and organic-fertilized soil), residue type (R; root, stem and leaf), and/or time (T) and their associated interaction on the dependent variables tested. Factor EOC 13 C- EOC MBC 13 C- MBC 13 C-EOC/ 13 Cresidue0 13 C-MBC/ 13 Cresidue0 13 C-EOC/ EOC 13 C-MBC/ MBC Soil fertilization (F) P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 Residue type (R) P < 0.001 P < 0.001 0.047 0.002 P < 0.001 0.04 P < 0.001 0.044 Time (T) P < 0.001 0.011 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 P < 0.001 F×R P < 0.001 0.001 0.039 P < 0.001 0.001 P < 0.001 0.12 P < 0.001 F×T P < 0.001 P < 0.001 P < 0.001 P < 0.001 0.002 P < 0.001 P < 0.001 P < 0.001 R×T P < 0.001 P < 0.001 0.002 P < 0.001 P < 0.001 0.07 P < 0.001 0.001 F×R×T 0.054 0.043 0.004 0.001 P < 0.001 0.018 P < 0.001 P < 0.001 a EOC, total extractable organic carbon; 13 C-EOC, EOC derived from residue C; MBC, total microbial biomass carbon; 13 C-MBC, MBC derived from residue C; 13 C-EOC/ 13 C residue0, percentage of 13 C-EOC in initial content of C in the residue; 13 C-MBC/ 13 Cresidue0, percentage of 13 C-MBC in initial content of C in the residue; 13 C-EOC/EOC, percentage of 13 C-EOC in EOC; 13 C-MBC/MBC, percentage of 13 C-MBC in MBC. The contribution of root and stem-derived residue C to EOC decreased with the incubation time in different fertilizer treatments (Table 3 ). At the end of incubation, a greater contribution of residue C to EOC was seen in the unfertilized soil compared with organic-fertilized soil. The contribution of residue-derived C to EOC was less than 12% in the unfertilized soil (Table 3 ), with the highest content of EOC derived from residue ( 13 C-EOC) (an average of 27 mg kg − 1 soil) (Fig. 2 a and b), on the first day. The 13 C-EOC value decreased sharply to 11 mg kg − 1 soil on the 28th day, and then slowly decreased in the unfertilized soil treated with residues till the end of incubation. A greater contribution of residue C to EOC treated with root was observed in the unfertilized than those in stem and leaf residues during the whole incubation (Table 3 ). The peak value of 13 C-EOC in the organic-fertilized soil, accounting for about 9.0% of EOC, occurred on the 28th day for the three residues (Table 3 ). After 180 days, the contribution of residue C derived from root to EOC (8.2%) was higher compared with residue C (4.9%) from leaf and stem in the organic-fertilized soil. Table 3 Relative contributions (%) of residue carbon in extractable organic carbon and microbial biomass carbon in long-term fertilization of soils added with maize root, steam and leaf residues, respectively Incubation time (days) Extractable organic carbon Microbial biomass carbon Root residue Stem residue Leaf residue Root residue Stem residue Leaf residue UF OF UF OF UF OF UF OF UF OF UF OF 1 11.4 ± 0.9 a * 8.7 ± 0.7 a 9.3 ± 0.8 b * 7.6 ± 0.4 b 6.8 ± 0.5 c * 5.7 ± 0.4 c 11.1 ± 1.0 b 25.0 ± 2.7 a * 13.2 ± 1.4 a 20.3 ± 2.2 b * 14.5 ± 1.2 a 22.2 ± 2.1 a * 7 7.2 ± 0.6 a 8.0 ± 0.4 a * 7.2 ± 0.7 a 6.9 ± 0.5 b 6.3 ± 0.5 b * 5.4 ± 0.5 c 19.4 ± 1.9 b 28.6 ± 2.6 a * 18.9 ± 1.5 b 21.0 ± 2.0 b * 22.4 ± 2.0 a 25.0 ± 2.3 a * 28 7.5 ± 0.5 a 8.6 ± 0.4 a * 5.5 ± 0.5 a 8.9 ± 0.5 a * 7.8 ± 0.5 a 9.1 ± 0.8 a * 14.1 ± 1.2 b 30.0 ± 2.8 a * 15.3 ± 1.4 b 23.6 ± 2.1 b * 18.8 ± 1.6 a 27.4 ± 2.7 a * 56 7.9 ± 0.4 a 8.0 ± 0.5 a 5.2 ± 0.4 b 7.0 ± 0.4 a * 5.4 ± 0.3 b 7.3 ± 0.7 a * 19.0 ± 1.6 b 35.1 ± 3.8 a * 17.4 ± 1.5 b 28.5 ± 2.6 b * 28.5 ± 2.7 a * 25.4 ± 2.4 c 180 9.1 ± 0.9 a * 8.2 ± 0.4 a 7.8 ± 0.5 b * 4.8 ± 0.2 b 5.9 ± 0.4 c * 4.9 ± 0.4 b 16.5 ± 1.5 b 49.0 ± 5.0 a * 18.0 ± 1.6 b 42.6 ± 4.3 b * 23.2 ± 2.0 a 31.7 ± 3.0 c * 360 8.6 ± 0.7 a 8.2 ± 0.7 a 7.2 ± 0.6 b * 4.8 ± 0.4 b 5.8 ± 0.4 c * 4.9 ± 0.4 b 12.0 ± 1.0 c 47.3 ± 4.0 a * 17.0 ± 1.5 b 50.2 ± 5.0 a * 20.5 ± 1.9 a 24.4 ± 2.2 b * a UF, unfertilized soil; OF, organic-fertilized soil. b Different lowercase letters show the significant differences ( P < 0.05) between different residue treatments at the same incubation time. c Stars show the significant differences ( P < 0.05) between different soil fertilization at the same residue treatment at the same incubation time. Contribution of maize residue C to MBC Soil fertilization and incubation time showed significant effects ( P < 0.05) on MBC (Table 2 and Fig. 1 c and d). MBC was initially 426 mg kg − 1 and 280 mg kg − 1 in the organic-fertilized soil and unfertilized soil, respectively (Fig. 1 c and d), and then decreased by 85% at the end of incubation (on the 360th day). During the whole incubation, residue type had no significant effect ( P > 0.05) on MBC in the unfertilized soil (Fig. 1 c). The MBC of organic-fertilized soil treated with stem residue was higher than those of root and leaf residues in the first 28 days of incubation, then increased by 22%~35% in the organic-fertilized soil treated with root residue compared with stem and leaf residues. More MBC was derived from residue C ( 13 C-MBC) in the organic-fertilized soil than that in the unfertilized soil (Fig. 2 c and d). The 13 C-MBC treated with leaf residue was greater than those from root and stem residue C (except after 1 day) in the unfertilized soil. And the percentages of 13 C-MBC ranged from 15–30% to the leaf residue, of which was 10–20% to the root and stem residues in the unfertilized soil (Table 3 ). The peaks of 13 C-MBC values were 42, 45 and 56 mg kg − 1 soil on the 7th day, and then the second maximum values were 37, 37 and 50 mg kg − 1 soil occurred on the 56th day in the unfertilized soil treated with root, stem and leaf residues, respectively (Fig. 2 c and d). The 13 C-MBC contents of organic-fertilized soil decreased from 100 mg kg − 1 soil on 1st day to 25 mg kg − 1 soil at the end of incubation. About 20%~50% of MBC was derived from residue C in the organic-fertilized soil during the whole incubation, especially on the 180th day and 360th day, it exceeded to 40% (Table 3 ). In addition, the 13 C-MBC contents derived from root residue was significantly greater ( P < 0.05) than that derived from leaf residue after 28 days of incubation in the organic-fertilized soil. Even at the later incubation stage (on the 180th day and 360th day), MBC derived from root residue C was 4 times greater than that derived from leaf residue C. Distribution of maize residue C in different soil C pools Overall, the distribution of root and stem derived C in EOC decreased with incubation time. In comparison, a peak distribution from leaf residue to EOC showed on the 28th day. At the end of incubation, the distribution of root-derived C in EOC was higher than those of stem and leaf derived C in both of unfertilized and organic-fertilized soils treatments. The distribution of maize residue C in MBC was higher in the organic-fertilized than that in the unfertilized soil treated with residues addition (Table 4 ). The two peak values in the distribution of residue C in MBC in the unfertilized were observed on the 7th day and 56th day, respectively (Table 4 ). However, the distribution of residue C in MBC decreased in the organic-fertilized soil during the whole incubation (Table 4 ). At the end of incubation, the distribution of leaf-derived C in MBC was higher than those of the stem and root-derived C in MBC in the unfertilized soil. However, in the organic-fertilized soil, less leaf-derived C was distributed to MBC compared with root and stem residues. Table 4 Distribution of residue carbon in extractable organic carbon and microbial biomass carbon (%) in long-term fertilization of soils added with maize root, stem and leaf, respectively Incubation time (days) Extractable organic carbon Microbial biomass carbon Root residue Stem residue Leaf residue Root residue Stem residue Leaf residue UF OF UF OF UF OF UF OF UF OF UF OF 1 5.7 ± 0.5 a * 4.4 ± 0.2 b 6.0 ± 0.5 a * 4.9 ± 0.2 a 4.0 ± 0.3 b * 3.3 ± 0.0 c 7.0 ± 0.1 b 18.1 ± 2.2 b * 7.3 ± 0.1 b 20.7 ± 2.1 a * 8.0 ± 0.7 a 19.7 ± 1.9 ab * 7 2.9 ± 0.1 b 4.2 ± 0.3 b * 3.9 ± 0.5 a 4.5 ± 0.9 a * 2.8 ± 0.3 b 3.6 ± 0.3 c * 8.7 ± 0.1 b 18.7 ± 1.2 a * 8.5 ± 0.3 b 13.6 ± 1.3 b * 11.1 ± 0.6 a 18.2 ± 1.1 a * 28 2.8 ± 0.1 a 4.8 ± 0.2 b * 2.2 ± 0.2 b 4.8 ± 1.0 b * 3.1 ± 0.7 a 5.5 ± 0.5 a * 5.9 ± 0.4 b 17.2 ± 0.4 a * 5.8 ± 0.7 b 12.7 ± 0.8 b * 7.8 ± 0.4 a 10.6 ± 0.2 c * 56 2.7 ± 0.2 a 4.4 ± 0.8 a * 1.9 ± 0.2 b 3.3 ± 0.2 c * 2.2 ± 0.2 b 3.8 ± 0.2 b * 7.7 ± 0.6 b 14.5 ± 1.4 a * 7.1 ± 0.4 b 11.4 ± 0.7 b * 11.2 ± 1.3 a * 10.6 ± 0.4 b 180 2.7 ± 0.1 a 3.8 ± 0.1 a * 2.8 ± 0.2 a * 1.8 ± 0.1 b 2.2 ± 0.1 b 2.1 ± 0.1 b 2.6 ± 0.0 a 10.0 ± 0.9 a * 2.8 ± 0.2 a 7.1 ± 0.3 b * 2.9 ± 0.3 a * 2.4 ± 0.7 c 360 2.8 ± 0.1 a 3.3 ± 0.2 a * 2.3 ± 0.3 b * 1.5 ± 0.1 b 1.5 ± 0.0 c 1.7 ± 0.1 b 1.4 ± 0.1 b 6.9 ± 1.1 a * 1.6 ± 0.0 b 6.5 ± 0.3 a * 2.4 ± 0.1 a 2.5 ± 0.1 b a UF, unfertilized soil; OF, organic-fertilized soil. b Different lowercase letters show the significant differences ( P < 0.05) between different residue treatments at the same incubation time. c Stars show the significant differences ( P < 0.05) between different soil fertilization at the same residue treatment at the same incubation time. Discussion Incorporation of residue C into EOC EOC and MBC are fractions of SOC that have rapid turnover rates and provide an easily accessible reservoir of C and nutrients (Choudhary et al. 2013). Fresh residue C addition can increase the content of EOC and MBC compared to soils with no residue addition because they provide C sources for soil microorganisms, and promote microbial growth (Jin et al. 2018 ; Perelo and Munch 2005 ). We found that more residue C was distributed in MBC (6.9% and 13.8%, in the unfertilized and organic-fertilized soil, respectively) compared with EOC (3.3% and 3.5%, in the unfertilized and organic-fertilized soils, respectively) for the whole residue amended treatments, which is consistent with previous results reported for this agricultural soil (An et al. 2015a ). Although EOC in soil without newly-added residue represents a major bioavailable substrate for microorganisms (De Troyer et al. 2011), as there may be preferential assimilation of dissolved organic C derived from residue C with rapid consumption rates (Kuzyakov and Jones, 2006 ). Soluble organic C is considered to be an important component for sequestering residue-derived C in soil (Choudhary et al. 2013). The EOC content in agricultural systems suggest that only a small portion of soluble organic C is derived from fresh plant residues (An et al. 2015a ; Blagodatskaya et al. 2011a ). We also found that only 1.5–2.3% of residue C remained in EOC for the all treatments after 1 year (Table 4 ). This is attributed to the fact that the soluble organics derived from newly-added residues are likely easily and preferentially degraded by microorganisms (Qiu et al 2015; Blagodatskaya et al. 2011b ). As expected, a greater contribution of residue C to EOC was observed on the first day of incubation. The soluble organic fraction from fresh residue addition is released to soils after several hours or days, which implies relatively rapid EOC uptake by active microorganisms (De Troyer et al. 2011). Our first hypothesis assumed that more aboveground residue C would be incorporated in the labile organic C. This was not confirmed at least in the EOC fraction regardless soil fertilization treatment (Fig. 2 a and b). Some studies have found that SOM formation from root residue C inputs exceed those of the aboveground C inputs (e.g. stem and leaf residues) (Kong and Six. 2010). We observed a greater contribution of root-derived C in EOC fractions compared with stem and leaf residues (Fig. 2 and b, and Table 3 ). This suggest that root exudates from living plant biomass would have a strong potential for the formation of mineral-associated organic carbon (Sokol et al. 2019 ). Therefore, root-derived C stabilizes more efficiently than stem and leaf residues and highlight the important roles of roots in improving labile SOC pools in these agricultural soils. In addition, the mean residence time in soils for root-derived C has been found to be higher than stem-derived C (Rasse et al. 2005 ). This may be attributed to the chemical composition of residues (such as higher lignin in root residue) (Lian et al. 2016 ). The interaction of lignin molecules and transformed products of lignin with soil quality are important for SOC stability than their intrinsic chemical recalcitrance (Rasse et al. 2006 ). Therefore, the proportional incorporation of root-derived residue C to the sequestration of EOC in the lab incubation of these agricultural soils was greater than that of aboveground residue C. The second hypothesis assumed that soil fertilization would affect the distribution of residue C in EOC. Indeed, greater distribution of residue C in EOC fractions was observed in the unfertilized soil than that of organic-fertilized soil. In addition, greater contribution of residue C in EOC was observed in the unfertilized soil than that in the organic-fertilized soil at the end of incubation (Table 3 ). This may be because a proportionally greater amount of degradable C was input to unfertilized soil, and this added fresh C was assimilated rapidly by “starving” C-limiting microorganisms (Bastida et al. 2013 ; Chen et al. 2018 ). Fresh residue C addition was easily assimilated as EOC by microorganisms in the unfertilized soil. In contrast, in the long-term organic manure application soil with more microbial biomass, the EOC derived from residue was preferentially used by microorganisms for energy production and was mostly released as CO 2 (unpublished data), thus a lower incorporation of maize residue C into the EOC fraction was observed in the organic-fertilized soil. Incorporation of residue C into MBC The peak value of MBC derived from residue C occurred at different periods in different soil fertilization (Fig. 2 c and d). This is consistent with the idea that residue availability is affected by initial nutrition and microbial activity of soils (An et al. 2015a ; Chen et al. 2018 ). For example, the continuous decrease of the MBC derived from residue C in the organic-fertilized soil can be attributed to faster turnover by higher microbial activity (as CO 2 released) in organic fertilizer treatment (unpublished). Microbial growth (and microbial biomass) depends on residue availability, which could be supported by the decrease of MBC after residue exhaustion (Shahbaz et al. 2017a ). In contrast, due to the low SOC level in the unfertilized soil compared with the organic-fertilized soil, excess fresh residue C may induce the fluctuating change of MBC by the fast- ( r -strategist) and slow-growing ( K -strategist) microorganisms in soil (John et al. 2003 ; Fontaine et al. 2003 ), this may be a result of substrate metabolized by microorganisms shifts with changes the residue availability (Perelo and Munch 2005 ). Therefore, the dynamic changes of microbial biomass are affected by the fresh residue addition to the agricultural soils of long-term soil fertilization. Contrary to our first hypothesis, we that more root-derived and stem-derived residue C was incorporated into MBC in the organic-fertilized soil, especially after 180 days of incubation (Table 3 ). The long-term application of organic manure not only increases soil fertility, but also alters soil microbial community and activity (Marschner et al. 2003 ). Maize stems could be preferentially utilized by microorganisms to incorporate into MBC because of their high carbohydrate concentrations (Clemente et al., 2013 ). Although root residue is observed to more slowly than stem and leaf residues (unpublished), root residue is still degraded and transformed to the stable SOC (Kuzyakov and Jones. 2006). It is possible that the portion of the microbial community utilizing more chemically complex C occupies a more dominant role in the organic-fertilized soil (Kiem and Kögel-Knabner 2013; Kramer and Gleixner 2006). Thus, more root and stem residues could be retained in organic-fertilized soil as stable SOC. In contrast, leaf residue contains a higher proportion of labile compounds (e.g. more sugar) that can be efficiently utilized by microorganisms, leading to larger microbial biomass than that from root- and stem-derived in previous studies, but only over the short-term (Cotrufo et al. 2013 ). In our study, more leaf-derived C was distributed to MBC compared with stem and root residues in the unfertilized soil (Table 4 ), as we hypothesised, which indicates that potentially greater substrate-use efficiency of leaf material. It is also possible that aboveground and belowground residues C are equally important to the formation of SOM, with their relative importance being driven by different environmental conditions (Sokol et al., 2019 ). For example, leaf litter leachate derived EOC contributes a major source of C to mineral C in forest ecosystems (Kaiser and Kalbitz. 2012). In addition, higher rates of transformation to SOM in leaf residue was observed in the C poor soil than that of the C rich soil (Miltner et al. 2012 ). The contribution of residue C to MBC is not only related to residue types but also to soil fertilization levels (Shahbaz et al. 2017a ). Our second hypothesis was not fully confirmed, at least in the MBC pool, as more distribution, and greater contribution, of residue C in MBC was observed in the organic-fertilized soil compared with the unfertilized soil (Tables 3 and 4 ). It has been widely observed that organic manure application markedly increases the MBC fraction (Gong et al. 2009 ; Ding et al. 2012 ). Long-term organic manure addition enhances the activity of microorganisms by providing a readily-available source of C substrate (Li et al. 2018 ; Jin et al. 2018 ), thereby increasing the conversion of residue C into MBC fraction. In addition, more residue-derived MBC in fertilized soil has been found in some laboratory experiments (Jin et al. 2018 ; Lian et al. 2016 ). Conversely, excess fresh C input into unfertilized soil with the insufficient nitrogen and/or phosphorous (Table 1 ) might limit the residue availability for microbial growth. Organic manure treatment is thus a significant a significant control on the transformation of residue C into microbial biomass as well as the stabilization of residue C in soil. Therefore, the residue-derived C contribution to MBC could be attributed with the initial soil C and nutrient background. Conclusion In summary, our results demonstrate that the incorporation of maize residue C into soil labile organic C pools (i.e., EOC and MBC) is strongly affected by residue type and soil fertilization. Specifically, root-derived C accumulated more in EOC and MBC than aboveground residue C in the organic-fertilized soil, but leaf-derived C accumulated more in MBC than those of root- and stem-derived C in the unfertilized soil, suggesting that root residue could lead to a greater potential labile C pool, which could constitute the primary C source for the microbial biomass and the precursor of stable SOC. This trend also indicates that the sequestration mechanisms of root vs . aboveground residues is regulated by soil fertilization, i.e., root-derived C may contribute more to stable SOC in the form of microbial products in the organic-fertilized soil, whereas leaf-derived C may be transformed into SOC more through the microbial synthesis in the unfertilized soil. Moreover, the contribution of residue C into EOC was greater in the unfertilized soil than that in the organic-fertilized soil, but more residue C was incorporated into MBC in the organic-fertilized soil than that in the unfertilized soil. This implies that the organic-fertilized soil should trigger a high C stabilization capacity following plant residue addition due to more microbial production, but the unfertilized soil was beneficial to promote the accumulation of plant residue in the form of EOC. Declarations Acknowledgements This study is supported by the National Natural Science Foundation of China (41977086, 41701330, 41771328). We are thankful to Shifeng Fu for technical support with the establishment of the experiment and elemental analyses. We also thankful to Jun Cui’s suggestions of this original manuscript. Ninghui Xie would like to thank China Scholarship Council for the financial support from the visiting scholar program. We thank the anonymous reviewers for their helpful comments that significantly improved the manuscript. References Amelung W, Brodowski S, Sandhage-Hofmann A, Bol R (2008) Combining biomarker with stable isotope analyses for assessing the transformation and turnover of soil organic matter. Adv Agron 100:155-250. An T, Schaeffer S, Zhuang J, Radosevich M, Li S, Li H, Pei J, Wang J (2015a) Dynamics and distribution of 13 C-labeled straw carbon by microorganisms as affected by soil fertility levels in the Black Soil region of Northeast China. 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Also discoverable on Platform About Our Team In Review Editorial Policies Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-341230","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":17653027,"identity":"57a2fcea-5e04-4560-a894-8aefc065afb9","order_by":0,"name":"Ninghui Xie","email":"","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ninghui","middleName":"","lastName":"Xie","suffix":""},{"id":17653028,"identity":"c0b1b950-fea1-4395-965f-086746e23b4c","order_by":1,"name":"Sean Michael Schaeffer","email":"","orcid":"","institution":"Department of Biosystems Engineering and Soil Science, University of Tennessee","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Sean","middleName":"Michael","lastName":"Schaeffer","suffix":""},{"id":17653029,"identity":"76dc1598-4cf5-4270-8d3a-1d1329dd5a00","order_by":2,"name":"Tingting An","email":"","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tingting","middleName":"","lastName":"An","suffix":""},{"id":17653030,"identity":"cc7d374d-0e13-42b8-8b83-cc6e9e81d8a9","order_by":3,"name":"Yingde Xu","email":"","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yingde","middleName":"","lastName":"Xu","suffix":""},{"id":17653031,"identity":"532f1d53-e0ad-40f5-a9c1-d210165131eb","order_by":4,"name":"Shuangyi Li","email":"","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shuangyi","middleName":"","lastName":"Li","suffix":""},{"id":17653032,"identity":"4bf97de1-985e-4403-99fc-a078a037e317","order_by":5,"name":"Liangjie Sun","email":"","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Liangjie","middleName":"","lastName":"Sun","suffix":""},{"id":17653033,"identity":"e0ee052f-8293-4b4c-866d-d4a50b026423","order_by":6,"name":"Jingkuan Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYBACxh4wZQPlshGvJY0ELQw8YPIwCVqYe84Yfi74dd7e4PgZA4YPZYcZ+Gc3EHBYb4+x9My+24kbzuQYMM44d5hB4s4BAlr6eTdI8/bcTjA4kGPAzNt2mMFAIoGgls2/eXvO2Rucf2PA/JcoLb2926R5fhxg3HADaAsjUVp6zn+z5m1ITpx541nBwZ5z6TwSNwhoMexJS77N88fOnu988sYHP8qs5fhnENLSALKqjYFB4QADAxBB4wkfkAeTf4CMBoJqR8EoGAWjYKQCANAgRtLAHHbZAAAAAElFTkSuQmCC","orcid":"","institution":"Shenyang Agricultural University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Jingkuan","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2021-03-18 07:17:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-341230/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-341230/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":7272323,"identity":"5ade9e63-0f12-4ec4-95ac-aa7254a0f55e","added_by":"auto","created_at":"2021-03-23 15:16:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":178930,"visible":true,"origin":"","legend":"The contents of extractable organic carbon (a and b) and microbial biomass carbon (c and d) in different soil fertilization added with 13C-labeled maize root, stem and leaf residues, respectively. Different lowercase letters show the significant differences (P \u003c 0.05) between different treatments at the same incubation time. ","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-341230/v1/d39762061d7035e4d92290d3.png"},{"id":7272094,"identity":"296c8968-7679-4d9a-9f0b-6a89ab739159","added_by":"auto","created_at":"2021-03-23 15:16:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":166190,"visible":true,"origin":"","legend":"The 13C contents of extractable organic carbon (a and b) and microbial biomass carbon (c and d) derived from residue carbon in different fertility level soils added with 13C-labeled maize root, stem and leaf residues, respectively. Different lowercase letters show the significant differences (P \u003c 0.05) between different treatments at the same incubation time. ","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-341230/v1/a24376584bc00f6c40b1174e.png"},{"id":13682215,"identity":"9b10300f-0e17-42b8-9643-31b28805a6e1","added_by":"auto","created_at":"2021-09-17 11:55:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":766572,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-341230/v1/6da21481-9b2f-4d4d-8b0b-c527a773ffa8.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eEffect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization\u003c/p\u003e","fulltext":[{"header":"Introduction","content":" \u003cp\u003eSoil organic carbon (SOC) sequestration is critical for agriculture and the environment, particularly in soil health and food security (Lal, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). SOC stocks are governed by the balance between carbon (C) input and output, and strongly affected by soil management practices (Paustian et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Adoption of plant residue retention methods are essential to maintain, or improve SOC content and the sustainability of agricultural systems (Lal \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Diacono et al. 2010). However, SOC dynamics induced by plant residue retention generally occurs slowly since the total SOC pool is too large to be affected in the short-term (Salinas-Garcia et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Ding et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). In this context, SOC fractions with relatively higher turnover rates and/or reactivity can be used to quantify the effect of agricultural management on soil quality (Silveira et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Specifically, soluble organic C and microbial biomass C (MBC) fractions respond more quickly to soil management activities than other C pools (Nieder et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Lehmann and Kleber \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePlant residues provide available substrate for soil microorganisms (Shahbaz et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2017a\u003c/span\u003e), and in turn play an important role in microbe-mediated biogeochemical processes (Ge et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Haubensak et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Plant residue can be preferentially utilized by microorganisms for biomass production during microbial growth processes (Liang et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Microorganisms solubilize plant-derived C through depolymerization by extracellular enzymes, and any net increase in the soluble C fraction is driven by microbial death, exudation, or a decrease in microbial assimilation (Burns et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Generally, the dynamics of microbial utilization of residue C and stabilization, for example, relative abundances of soluble organic C and MBC, are mainly mediated by plant residue quality (Chen et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Prescott \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Liang et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In the traditional view, root residue is relatively recalcitrant, and has a slower decomposition rate, thus more root C is incorporated into the stable SOC fractions than that from stem and leaf residues (Lian et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Johnson et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). However, a prevailing counter hypothesis proposes that labile C compounds can contribute more to long-term soil C stability than highly recalcitrant chemical compounds such as lignin (Amelung et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Schmidt et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Lehmann and Kleber \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This is because above-ground residues (e.g. stem and leaf residues) contain more easily degradable C, which plays a significant role in labile organic C accumulation, and subsequently, may contribute more to SOC sequestration due to high microbial utilization efficiency (Don and Kalbitz \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Cotrufo et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These new theories challenge our understanding of the mechanisms of how root \u003cem\u003evs\u003c/em\u003e. aboveground residues is involved in SOC formation. Therefore, given the important role of labile C in the SOC accumulation, it is necessary to strengthen our knowledge of the impacts of plant residue type on the microbial assimilation of exogenous C and the dynamics of soil labile C, i.e., soluble organic C and MBC.\u003c/p\u003e \u003cp\u003eSoil fertilization and total SOC are important factors controlling microbial assimilation of plant residue (Wang et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Zhu et al. 2016; Marschner et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). The dynamics and distribution of residue C in soil depends upon soil fertility under long-term soil fertilization regimes because more residue C tends to accumulate in MBC in low fertility soil compared with high fertility soil (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e). However, the combined applications of plant residues (leaf, stems and roots) in soils may differentially affect proportional labile organic C accumulation, resulting in differences in residue C accumulation in the total SOC pool of the soils with different levels of SOC (Lian et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Because microbial competition for residue C depends upon initial soil properties (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e), the application of organic fertilizers, which enhance soil fertility (Macci et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Jin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), is expected to affect microbial utilization of plant residues. In general, the addition of residue C to soil enhances soil labile organic pools (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e), but the additions of different quality residues in soils with different levels of SOC and nutrients determine its accumulation (Singh et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Fang et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The effect of soil fertilization on the incorporation of different types of maize residues into labile C pools has received far less attention.\u003c/p\u003e \u003cp\u003eThe objectives of our research were: (1) to quantify the contribution of different types of maize residue to soluble organic C, measured as extractable organic C (EOC), and MBC and (2) to determine the differences in distribution and utilization of residue C in long-term soil fertilization among residue types. We added the \u003csup\u003e13\u003c/sup\u003eC-labeled maize residues (leaf, stem and root) to unfertilized and organic-fertilized soils and incubated the soils for 360 days. The percentages of different residue C in EOC and MBC fractions were determined. The incubation study was designed to test the following hypotheses: (1) plant residue addition would increase the labile organic C, with its magnitude depending on the residue types, i.e., more aboveground residue C would be incorporated in labile organic C than root residue C; (2) soil fertilization would regulate the distribution of plant residue C in EOC and MBC, and the greater distribution of residue C in labile organic C would be in unfertilized soil because of C deficiency than organic-fertilized soil.\u003c/p\u003e "},{"header":"Materials And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003eExperimental site and soil sampling\u003c/h2\u003e\n\u003cp\u003eSoil samples were collected from a long-term fertilization experiment station (41\u0026deg;49\u0026rsquo;N, 123\u0026deg;34\u0026rsquo;E) that was established in 1987 at Shenyang Agricultural University, Liaoning, China. This region is characterized by a typical continental monsoon climate, with annual mean temperature of 7.9 \u003csup\u003eo\u003c/sup\u003eC and annual mean precipitation of 705 mm. The soil type is Brown Earth according to the Chinese Soil Taxonomy (a Hapli-Udic Alfisol according to the USDA Taxonomy, Soil Survey Staff, \u003cspan class=\"CitationRef\"\u003e1999\u003c/span\u003e). The cropping system is monoculture maize which is sown in early May and harvested in early October each year. A detailed description of this site was given by An et al. (\u003cspan class=\"CitationRef\"\u003e2015b\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eField plots with two fertility levels were selected for this study: (1) no fertilizer application (unfertilized soil); (2) application of composted swine manure (270 kg N ha y\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) for more than 27 years (organic-fertilized soil). The compost contained 150 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total organic C; 10 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total N; 10 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and 4 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csub\u003e2\u003c/sub\u003eO on a dry weight basis (An et al. \u003cspan class=\"CitationRef\"\u003e2015a\u003c/span\u003e). In each plot, a total of five samples were randomly collected, and then fully mixed to form one composite soil sample to represent each experimental plot. Soil samples (0\u0026ndash;20 cm depth) were collected in November, 2014, and all visible crop roots and debris were removed, then all the soil samples were sieved (2mm) and air-dried for the subsequent incubation experiment. The main soil properties of the soil samples are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab1\" style=\"width: 849px;\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eBasic characteristics of soil samples in long-term fertilization of soils (in 2014)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 96px;\" align=\"left\"\u003e\n\u003cp\u003eSoil\u003c/p\u003e\n\u003cp\u003efertilization\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 93px;\" align=\"left\"\u003e\n\u003cp\u003eTotal soil\u003c/p\u003e\n\u003cp\u003eorganic carbon\u003c/p\u003e\n\u003cp\u003e(g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 82px;\" align=\"left\"\u003e\n\u003cp\u003e\u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003c/p\u003e\n\u003cp\u003e(\u0026permil;)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 72px;\" align=\"left\"\u003e\n\u003cp\u003eTotal\u003c/p\u003e\n\u003cp\u003enitrogen\u003c/p\u003e\n\u003cp\u003e(N, g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003eTotal\u003c/p\u003e\n\u003cp\u003ephosphorus\u003c/p\u003e\n\u003cp\u003e(P, g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 64px;\" align=\"left\"\u003e\n\u003cp\u003eC/N\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003eC/P\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 71px;\" align=\"left\"\u003e\n\u003cp\u003eClay\u003c/p\u003e\n\u003cp\u003e(%)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 64px;\" align=\"left\"\u003e\n\u003cp\u003epH\u003c/p\u003e\n\u003cp\u003e(H\u003csub\u003e2\u003c/sub\u003eO)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 98px;\" align=\"left\"\u003e\n\u003cp\u003eMicrobial\u003c/p\u003e\n\u003cp\u003ebiomass carbon\u003c/p\u003e\n\u003cp\u003e(mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 96px;\" align=\"left\"\u003e\n\u003cp\u003eUnfertilized\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 93px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e10.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 82px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e-17.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 72px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e1.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e4.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 64px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e8.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e2.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 71px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e17.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 64px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e6.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 98px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e117.69\u0026thinsp;\u0026plusmn;\u0026thinsp;3.25\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 96px;\" align=\"left\"\u003e\n\u003cp\u003eOrganic-fertilized\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 93px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e17.80\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 82px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e-19.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 72px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e2.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e22.77\u0026thinsp;\u0026plusmn;\u0026thinsp;2.48\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 64px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e8.10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e0.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 71px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e18.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 64px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e6.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 98px;\" align=\"char\" char=\"\u0026plusmn;\"\u003e\n\u003cp\u003e163.54\u0026thinsp;\u0026plusmn;\u0026thinsp;5.23\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e Unfertilized: long-term no fertilization soil; Organic-fertilized: long-term organic manure fertilization soil.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003e Stars show the significant differences (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between soil fertilizations at the same indicator.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e\u0026nbsp;\u003c/h2\u003e\n\u003ch2\u003ePreparation of \u003csup\u003e13\u003c/sup\u003eC-labeled maize residue\u003c/h2\u003e\n\u003cp\u003eRoot, stem and leaf residue were obtained from fully matured maize plants that had been pulse-labeled with \u003csup\u003e13\u003c/sup\u003eCO\u003csub\u003e2\u003c/sub\u003e (98 atom %) for six times across the whole growth stages in 2014 (An et al. \u003cspan class=\"CitationRef\"\u003e2015b\u003c/span\u003e). The aboveground plant was cut at the root base and then stem and leaf residues were carefully collected. The main and lateral roots were gently separated from soil and then washed off the adhering soil with tap water. All the sampled residues were oven-dried at 70 ℃ for 12 h. Five plants (root, stem, and leaf, respectively) were randomly selected from all the labeling maize plants and then chopped 5 mm segments. After that, the residues were selected by the quartering methods and then ground into less than 0.5-mm segments. Root residue contained 400 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total organic C, 12.6 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total N, 394\u0026permil; \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value, and C/N ratio of 32. Stem residue contained 440 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total organic C, 14.5 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total N, 696\u0026permil; \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value, and C/N ratio of 30. Leaf residue contained 421 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total organic C, 12.7 g kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total N, 662\u0026permil; \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value, and C/N ratio of 33.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n\u003ch2\u003eIncubation experiment\u003c/h2\u003e\n\u003cp\u003eAir-dried soil sample (120 g) was weighted into 500 ml incubation vessels. Soil was then pre-incubated at 35% of its water holding capacity (WHC) at 25 \u0026ordm;C for 7 days, because sieving affects the availability of soil organic matter (SOM) for soil microorganisms (An et al. \u003cspan class=\"CitationRef\"\u003e2015a\u003c/span\u003e). The pre-incubated soil samples were amended with root, stem and leaf residues (1% of oven-dried soil weight), respectively. No amendment was applied in the control treatment. The added residues were thoroughly mixed with incubated soil. The glass vessels were sealed with parafilm, and several tiny holes were drilled in the parafilm in order to allow gas going through while retarding soil water evaporation (Wang et al. \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). Soil samples were incubated at 25℃ at 60% WHC for 360 days under darkness. Periodically, the vessels were weighed, and the soil water content was maintained at the original soil moisture level throughout the incubation period by supplementation with distilled water. Three replicates of each treatment were randomly and destructively sampled on the 1st, 7th, 28th, 56th, 180th and 360th day after incubation. A part of the sample was stored at 4 ℃ for EOC and MBC analysis. While the other part was air-dried, ground through 0.15 mm sieve and analyzed for SOC content and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003eMBC and EOC determination\u003c/h2\u003e\n\u003cp\u003eMBC was determined using chloroform-fumigation extraction (Vance et al. \u003cspan class=\"CitationRef\"\u003e1987\u003c/span\u003e). Briefly, fresh soil samples (equivalent to 10 g oven-dried soil) were fumigated with purified CHCl\u003csub\u003e3\u003c/sub\u003e for 24 h in the dark at 25 \u003csup\u003eo\u003c/sup\u003eC. After fumigation, the soil samples were extracted with 0.5 M K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e at 1:4 soil: solution ratio. An equivalent amount of non-fumigated soil was also extracted when fumigation commenced. The organic C of the non-fumigated extract was the EOC (Schaeffer et al. \u003cspan class=\"CitationRef\"\u003e2013\u003c/span\u003e). The organic C content of soil extract was determined with the Total Organic Carbon Analyzer (Elementar High TOC II, Germany). MBC was calculated as the difference in organic C content between fumigated and non-fumigated soil extracts with a correction factor (\u003cem\u003ek\u003c/em\u003e\u003csub\u003e\u003cem\u003eEC\u003c/em\u003e\u003c/sub\u003e) of 0.45 (Wu et al. \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e). All K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e-extract aliquots (20 ml) were freeze-dried for the determination of \u003csup\u003e13\u003c/sup\u003eC abundances.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n\u003ch2\u003eIsotopic C analysis and calculation\u003c/h2\u003e\n\u003cp\u003eAnalyses of the organic C contents and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC values in soil were conducted in an elemental analyzer (Elementar Vario PYRO cube, Germany) coupled to an isotope ratio mass spectrometer (IsoPrime 100 Isotope Ratio Mass Spectrometer, Germany). \u0026delta;\u003csup\u003e13\u003c/sup\u003eC values of K\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e extract samples were also determined in the same way. The \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value was expressed in parts per mil (\u0026permil;) relative to the international standard Pee Dee Belemnite (PDB) (Werner and Brand \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value of MBC (\u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003eMBC\u003c/sub\u003e, \u0026permil;) was calculated as follows:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" alt=\"\" /\u003e\u003c/p\u003e\n\u003cp\u003ewhere C\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003e\u003cem\u003eF\u003c/em\u003e\u003c/sub\u003e are the total organic C content (mg kg soil\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value (\u0026permil;) in the fumigated extracts, respectively, and C\u003csub\u003eNF\u003c/sub\u003e and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003e\u003cem\u003eNF\u003c/em\u003e\u003c/sub\u003e are the total organic C content (mg kg soil\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value (\u0026permil;) in the non-fumigated extracts, respectively.\u003c/p\u003e\n\u003cp\u003eThe percentage (\u003cem\u003ef\u003c/em\u003e, %) of maize residue C in MBC and EOC was calculated according to De Troyer et al. (2011):\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\" alt=\"\" /\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003e\u003cem\u003esample\u003c/em\u003e\u003c/sub\u003e is the \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value (\u0026permil;) of C pool in soil sample treated with maize residue, \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003e\u003cem\u003econtrol\u003c/em\u003e\u003c/sub\u003e is the \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value (\u0026permil;) of C pool do the corresponding soil sample without maize residue addition and \u0026delta;\u003csup\u003e13\u003c/sup\u003eC\u003csub\u003e\u003cem\u003eresidue0\u003c/em\u003e\u003c/sub\u003e is the \u0026delta;\u003csup\u003e13\u003c/sup\u003eC value of the applied maize residue.\u003c/p\u003e\n\u003cp\u003eThe content of C pool derived from residue C (C\u003csub\u003e\u003cem\u003eresidue\u003c/em\u003e\u003c/sub\u003e) was calculated with the following equation (Blaud et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e):\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/p\u003e\n\u003cp\u003ewhere C\u003csub\u003e\u003cem\u003esample\u003c/em\u003e\u003c/sub\u003e is the total content of C pool in EOC and MBC.\u003c/p\u003e\n\u003cp\u003eRepeated measures analysis was performed for all data over time, using a linear mixed model consisting of fixed effects of soil fertilization (unfertilized and organic-fertilized soil), plant residue types (maize root, stem and leaf), and time and their associated interaction, and random effects of replicates and replicates by time. All repeated measurements satisfy the assumption of sphericity. To allow for correlation between repeated measures on the same treatment, a first-order antedependence correlation model was assumed for the residuals within a plot (Fang et al., \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e). Differences between soil fertilizations were assessed by paired T-test. All statistical analyses were performed with IBM SPSS 19.0 (IBM, USA) software package with significant differences at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 level. Graphs were drawn using Origin 8 (Origin Lab, USA).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n\u003ch2\u003eContribution of maize residue C to EOC\u003c/h2\u003e\n\u003cp\u003eSoil fertilization and residue type significantly affected (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) the contents of EOC (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). EOC decreased from 241 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil to 138 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea and b) during the incubation time. And it was 1\u0026ndash;2 times higher in the organic-fertilized soil than that in the unfertilized soil treated with residues. The content of EOC in the unfertilized soil treated with root residue was lower than those treated with stem and leaf residues during the whole incubation. However, the opposite trend was observed in the organic-fertilized soil treated with residues after 56 days. At the end of incubation (360th day), the EOC content in the organic-fertilized soil added with root residue was about 30% higher than those of stem and leaf residues.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab2\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eStatistical significance (\u003cem\u003eP\u003c/em\u003e values) of the fixed terms of soil fertilization (F; unfertilized soil and organic-fertilized soil), residue type (R; root, stem and leaf), and/or time (T) and their associated interaction on the dependent variables tested.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eFactor\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eEOC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-\u003c/p\u003e\n\u003cp\u003eEOC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMBC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-\u003c/p\u003e\n\u003cp\u003eMBC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-EOC/\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eCresidue0\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-MBC/\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eCresidue0\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-EOC/\u003c/p\u003e\n\u003cp\u003eEOC\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003e\u003csup\u003e13\u003c/sup\u003eC-MBC/\u003c/p\u003e\n\u003cp\u003eMBC\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSoil fertilization (F)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eResidue type (R)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.047\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.002\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.04\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.044\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTime\u003c/p\u003e\n\u003cp\u003e(T)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.011\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eF\u0026times;R\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.039\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.12\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eF\u0026times;T\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.002\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eR\u0026times;T\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.002\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.07\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eF\u0026times;R\u0026times;T\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.054\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.043\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.004\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.018\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e EOC, total extractable organic carbon; \u003csup\u003e13\u003c/sup\u003eC-EOC, EOC derived from residue C; MBC, total microbial biomass carbon; \u003csup\u003e13\u003c/sup\u003eC-MBC, MBC derived from residue C; \u003csup\u003e13\u003c/sup\u003eC-EOC/\u003csup\u003e13\u003c/sup\u003eC residue0, percentage of \u003csup\u003e13\u003c/sup\u003eC-EOC in initial content of C in the residue; \u003csup\u003e13\u003c/sup\u003eC-MBC/\u003csup\u003e13\u003c/sup\u003eCresidue0, percentage of \u003csup\u003e13\u003c/sup\u003eC-MBC in initial content of C in the residue; \u003csup\u003e13\u003c/sup\u003eC-EOC/EOC, percentage of \u003csup\u003e13\u003c/sup\u003eC-EOC in EOC; \u003csup\u003e13\u003c/sup\u003eC-MBC/MBC, percentage of \u003csup\u003e13\u003c/sup\u003eC-MBC in MBC.\u003c/p\u003e\n\u003c/div\u003e\n\u003cp\u003eThe contribution of root and stem-derived residue C to EOC decreased with the incubation time in different fertilizer treatments (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). At the end of incubation, a greater contribution of residue C to EOC was seen in the unfertilized soil compared with organic-fertilized soil. The contribution of residue-derived C to EOC was less than 12% in the unfertilized soil (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), with the highest content of EOC derived from residue (\u003csup\u003e13\u003c/sup\u003eC-EOC) (an average of 27 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and b), on the first day. The \u003csup\u003e13\u003c/sup\u003eC-EOC value decreased sharply to 11 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil on the 28th day, and then slowly decreased in the unfertilized soil treated with residues till the end of incubation. A greater contribution of residue C to EOC treated with root was observed in the unfertilized than those in stem and leaf residues during the whole incubation (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The peak value of \u003csup\u003e13\u003c/sup\u003eC-EOC in the organic-fertilized soil, accounting for about 9.0% of EOC, occurred on the 28th day for the three residues (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). After 180 days, the contribution of residue C derived from root to EOC (8.2%) was higher compared with residue C (4.9%) from leaf and stem in the organic-fertilized soil.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eRelative contributions (%) of residue carbon in extractable organic carbon and microbial biomass carbon in long-term fertilization of soils added with maize root, steam and leaf residues, respectively\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003cth style=\"height: 105px;\" rowspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eIncubation\u003c/p\u003e\n\u003cp\u003etime (days)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eExtractable organic carbon\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eMicrobial biomass carbon\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eRoot residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStem residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eLeaf residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eRoot residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStem residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eLeaf residue\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 35px;\"\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"height: 35px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr style=\"height: 61px;\"\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e9.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 c\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e13.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e20.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e22.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 61px;\"\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e6.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e19.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e28.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e18.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e21.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e22.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e25.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 61px;\"\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e9.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e14.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e30.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.8 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e15.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e23.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e18.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e27.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 61px;\"\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e56\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e19.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e35.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.8 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e17.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e28.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e28.5\u0026thinsp;\u0026plusmn;\u0026thinsp;2.7 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e25.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.4\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 61px;\"\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e180\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e9.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e5.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 c\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e16.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e49.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e18.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.6 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e42.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.3 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e23.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.0 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61px;\" align=\"left\"\u003e\n\u003cp\u003e31.7\u0026thinsp;\u0026plusmn;\u0026thinsp;3.0\u003c/p\u003e\n\u003cp\u003ec\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr style=\"height: 61.375px;\"\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e360\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e8.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e7.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 c\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e12.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e47.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.0 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e17.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e50.2\u0026thinsp;\u0026plusmn;\u0026thinsp;5.0 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e20.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9 a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"height: 61.375px;\" align=\"left\"\u003e\n\u003cp\u003e24.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e UF, unfertilized soil; OF, organic-fertilized soil.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003e Different lowercase letters show the significant differences (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between different residue treatments at the same incubation time.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ec\u003c/sup\u003e Stars show the significant differences (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between different soil fertilization at the same residue treatment at the same incubation time.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n\u003ch2\u003eContribution of maize residue C to MBC\u003c/h2\u003e\n\u003cp\u003eSoil fertilization and incubation time showed significant effects (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) on MBC (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec and d). MBC was initially 426 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 280 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the organic-fertilized soil and unfertilized soil, respectively (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec and d), and then decreased by 85% at the end of incubation (on the 360th day). During the whole incubation, residue type had no significant effect (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) on MBC in the unfertilized soil (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec). The MBC of organic-fertilized soil treated with stem residue was higher than those of root and leaf residues in the first 28 days of incubation, then increased by 22%~35% in the organic-fertilized soil treated with root residue compared with stem and leaf residues.\u003c/p\u003e\n\u003cp\u003eMore MBC was derived from residue C (\u003csup\u003e13\u003c/sup\u003eC-MBC) in the organic-fertilized soil than that in the unfertilized soil (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec and d). The \u003csup\u003e13\u003c/sup\u003eC-MBC treated with leaf residue was greater than those from root and stem residue C (except after 1 day) in the unfertilized soil. And the percentages of \u003csup\u003e13\u003c/sup\u003eC-MBC ranged from 15\u0026ndash;30% to the leaf residue, of which was 10\u0026ndash;20% to the root and stem residues in the unfertilized soil (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The peaks of \u003csup\u003e13\u003c/sup\u003eC-MBC values were 42, 45 and 56 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil on the 7th day, and then the second maximum values were 37, 37 and 50 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil occurred on the 56th day in the unfertilized soil treated with root, stem and leaf residues, respectively (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec and d). The \u003csup\u003e13\u003c/sup\u003eC-MBC contents of organic-fertilized soil decreased from 100 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003esoil on 1st day to 25 mg kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e soil at the end of incubation. About 20%~50% of MBC was derived from residue C in the organic-fertilized soil during the whole incubation, especially on the 180th day and 360th day, it exceeded to 40% (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). In addition, the \u003csup\u003e13\u003c/sup\u003eC-MBC contents derived from root residue was significantly greater (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) than that derived from leaf residue after 28 days of incubation in the organic-fertilized soil. Even at the later incubation stage (on the 180th day and 360th day), MBC derived from root residue C was 4 times greater than that derived from leaf residue C.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n\u003ch2\u003eDistribution of maize residue C in different soil C pools\u003c/h2\u003e\n\u003cp\u003eOverall, the distribution of root and stem derived C in EOC decreased with incubation time. In comparison, a peak distribution from leaf residue to EOC showed on the 28th day. At the end of incubation, the distribution of root-derived C in EOC was higher than those of stem and leaf derived C in both of unfertilized and organic-fertilized soils treatments.\u003c/p\u003e\n\u003cp\u003eThe distribution of maize residue C in MBC was higher in the organic-fertilized than that in the unfertilized soil treated with residues addition (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). The two peak values in the distribution of residue C in MBC in the unfertilized were observed on the 7th day and 56th day, respectively (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). However, the distribution of residue C in MBC decreased in the organic-fertilized soil during the whole incubation (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). At the end of incubation, the distribution of leaf-derived C in MBC was higher than those of the stem and root-derived C in MBC in the unfertilized soil. However, in the organic-fertilized soil, less leaf-derived C was distributed to MBC compared with root and stem residues.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003ctable id=\"Tab4\" style=\"width: 804px;\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eDistribution of residue carbon in extractable organic carbon and microbial biomass carbon (%) in long-term fertilization of soils added with maize root, stem and leaf, respectively\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 73px;\" rowspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eIncubation\u003c/p\u003e\n\u003cp\u003etime (days)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 505px;\" colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eExtractable organic carbon\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 440px;\" colspan=\"6\" align=\"left\"\u003e\n\u003cp\u003eMicrobial biomass carbon\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 164px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eRoot residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 165px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStem residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 176px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eLeaf residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 183px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eRoot residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 143px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eStem residue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 114px;\" colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eLeaf residue\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003cth style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003eUF\u003c/p\u003e\n\u003c/th\u003e\n\u003cth style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003eOF\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e4.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e4.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e4.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e18.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e7.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e20.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.1 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e8.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e19.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.9\u003c/p\u003e\n\u003cp\u003eab\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e4.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003ec\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e8.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e18.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e13.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e18.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e28\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e3.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e5.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e17.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e12.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e7.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ec\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e56\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e4.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e1.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ec\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e7.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e14.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 b\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e11.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e180\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e1.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e2.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e2.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e2.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e10.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9 a\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e7.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e360\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 78px;\" align=\"left\"\u003e\n\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 86px;\" align=\"left\"\u003e\n\u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e2.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003eb\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 85px;\" align=\"left\"\u003e\n\u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 99px;\" align=\"left\"\u003e\n\u003cp\u003e1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e\n\u003cp\u003ec\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 77px;\" align=\"left\"\u003e\n\u003cp\u003e1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 103px;\" align=\"left\"\u003e\n\u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 80px;\" align=\"left\"\u003e\n\u003cp\u003e6.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 70px;\" align=\"left\"\u003e\n\u003cp\u003e1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 73px;\" align=\"left\"\u003e\n\u003cp\u003e6.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n\u003cp\u003ea\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003ea\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd style=\"width: 57px;\" align=\"left\"\u003e\n\u003cp\u003e2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n\u003cp\u003eb\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e UF, unfertilized soil; OF, organic-fertilized soil.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003e Different lowercase letters show the significant differences (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between different residue treatments at the same incubation time.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ec\u003c/sup\u003e Stars show the significant differences (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between different soil fertilization at the same residue treatment at the same incubation time.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":" \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eIncorporation of residue C into EOC\u003c/h2\u003e \u003cp\u003eEOC and MBC are fractions of SOC that have rapid turnover rates and provide an easily accessible reservoir of C and nutrients (Choudhary et al. 2013). Fresh residue C addition can increase the content of EOC and MBC compared to soils with no residue addition because they provide C sources for soil microorganisms, and promote microbial growth (Jin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Perelo and Munch \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). We found that more residue C was distributed in MBC (6.9% and 13.8%, in the unfertilized and organic-fertilized soil, respectively) compared with EOC (3.3% and 3.5%, in the unfertilized and organic-fertilized soils, respectively) for the whole residue amended treatments, which is consistent with previous results reported for this agricultural soil (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e). Although EOC in soil without newly-added residue represents a major bioavailable substrate for microorganisms (De Troyer et al. 2011), as there may be preferential assimilation of dissolved organic C derived from residue C with rapid consumption rates (Kuzyakov and Jones, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSoluble organic C is considered to be an important component for sequestering residue-derived C in soil (Choudhary et al. 2013). The EOC content in agricultural systems suggest that only a small portion of soluble organic C is derived from fresh plant residues (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e; Blagodatskaya et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011a\u003c/span\u003e). We also found that only 1.5\u0026ndash;2.3% of residue C remained in EOC for the all treatments after 1 year (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This is attributed to the fact that the soluble organics derived from newly-added residues are likely easily and preferentially degraded by microorganisms (Qiu et al 2015; Blagodatskaya et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2011b\u003c/span\u003e). As expected, a greater contribution of residue C to EOC was observed on the first day of incubation. The soluble organic fraction from fresh residue addition is released to soils after several hours or days, which implies relatively rapid EOC uptake by active microorganisms (De Troyer et al. 2011). Our first hypothesis assumed that more aboveground residue C would be incorporated in the labile organic C. This was not confirmed at least in the EOC fraction regardless soil fertilization treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and b). Some studies have found that SOM formation from root residue C inputs exceed those of the aboveground C inputs (e.g. stem and leaf residues) (Kong and Six. 2010). We observed a greater contribution of root-derived C in EOC fractions compared with stem and leaf residues (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e and b, and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This suggest that root exudates from living plant biomass would have a strong potential for the formation of mineral-associated organic carbon (Sokol et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Therefore, root-derived C stabilizes more efficiently than stem and leaf residues and highlight the important roles of roots in improving labile SOC pools in these agricultural soils. In addition, the mean residence time in soils for root-derived C has been found to be higher than stem-derived C (Rasse et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). This may be attributed to the chemical composition of residues (such as higher lignin in root residue) (Lian et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The interaction of lignin molecules and transformed products of lignin with soil quality are important for SOC stability than their intrinsic chemical recalcitrance (Rasse et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Therefore, the proportional incorporation of root-derived residue C to the sequestration of EOC in the lab incubation of these agricultural soils was greater than that of aboveground residue C.\u003c/p\u003e \u003cp\u003eThe second hypothesis assumed that soil fertilization would affect the distribution of residue C in EOC. Indeed, greater distribution of residue C in EOC fractions was observed in the unfertilized soil than that of organic-fertilized soil. In addition, greater contribution of residue C in EOC was observed in the unfertilized soil than that in the organic-fertilized soil at the end of incubation (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This may be because a proportionally greater amount of degradable C was input to unfertilized soil, and this added fresh C was assimilated rapidly by \u0026ldquo;starving\u0026rdquo; C-limiting microorganisms (Bastida et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Chen et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Fresh residue C addition was easily assimilated as EOC by microorganisms in the unfertilized soil. In contrast, in the long-term organic manure application soil with more microbial biomass, the EOC derived from residue was preferentially used by microorganisms for energy production and was mostly released as CO\u003csub\u003e2\u003c/sub\u003e (unpublished data), thus a lower incorporation of maize residue C into the EOC fraction was observed in the organic-fertilized soil.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eIncorporation of residue C into MBC\u003c/h2\u003e \u003cp\u003eThe peak value of MBC derived from residue C occurred at different periods in different soil fertilization (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and d). This is consistent with the idea that residue availability is affected by initial nutrition and microbial activity of soils (An et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015a\u003c/span\u003e; Chen et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). For example, the continuous decrease of the MBC derived from residue C in the organic-fertilized soil can be attributed to faster turnover by higher microbial activity (as CO\u003csub\u003e2\u003c/sub\u003e released) in organic fertilizer treatment (unpublished). Microbial growth (and microbial biomass) depends on residue availability, which could be supported by the decrease of MBC after residue exhaustion (Shahbaz et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2017a\u003c/span\u003e). In contrast, due to the low SOC level in the unfertilized soil compared with the organic-fertilized soil, excess fresh residue C may induce the fluctuating change of MBC by the fast- (\u003cem\u003er\u003c/em\u003e-strategist) and slow-growing (\u003cem\u003eK\u003c/em\u003e-strategist) microorganisms in soil (John et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Fontaine et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), this may be a result of substrate metabolized by microorganisms shifts with changes the residue availability (Perelo and Munch \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Therefore, the dynamic changes of microbial biomass are affected by the fresh residue addition to the agricultural soils of long-term soil fertilization.\u003c/p\u003e \u003cp\u003eContrary to our first hypothesis, we that more root-derived and stem-derived residue C was incorporated into MBC in the organic-fertilized soil, especially after 180 days of incubation (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The long-term application of organic manure not only increases soil fertility, but also alters soil microbial community and activity (Marschner et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Maize stems could be preferentially utilized by microorganisms to incorporate into MBC because of their high carbohydrate concentrations (Clemente et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Although root residue is observed to more slowly than stem and leaf residues (unpublished), root residue is still degraded and transformed to the stable SOC (Kuzyakov and Jones. 2006). It is possible that the portion of the microbial community utilizing more chemically complex C occupies a more dominant role in the organic-fertilized soil (Kiem and K\u0026ouml;gel-Knabner 2013; Kramer and Gleixner 2006). Thus, more root and stem residues could be retained in organic-fertilized soil as stable SOC. In contrast, leaf residue contains a higher proportion of labile compounds (e.g. more sugar) that can be efficiently utilized by microorganisms, leading to larger microbial biomass than that from root- and stem-derived in previous studies, but only over the short-term (Cotrufo et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In our study, more leaf-derived C was distributed to MBC compared with stem and root residues in the unfertilized soil (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), as we hypothesised, which indicates that potentially greater substrate-use efficiency of leaf material. It is also possible that aboveground and belowground residues C are equally important to the formation of SOM, with their relative importance being driven by different environmental conditions (Sokol et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). For example, leaf litter leachate derived EOC contributes a major source of C to mineral C in forest ecosystems (Kaiser and Kalbitz. 2012). In addition, higher rates of transformation to SOM in leaf residue was observed in the C poor soil than that of the C rich soil (Miltner et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe contribution of residue C to MBC is not only related to residue types but also to soil fertilization levels (Shahbaz et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2017a\u003c/span\u003e). Our second hypothesis was not fully confirmed, at least in the MBC pool, as more distribution, and greater contribution, of residue C in MBC was observed in the organic-fertilized soil compared with the unfertilized soil (Tables\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). It has been widely observed that organic manure application markedly increases the MBC fraction (Gong et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Ding et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Long-term organic manure addition enhances the activity of microorganisms by providing a readily-available source of C substrate (Li et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Jin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), thereby increasing the conversion of residue C into MBC fraction. In addition, more residue-derived MBC in fertilized soil has been found in some laboratory experiments (Jin et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Lian et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Conversely, excess fresh C input into unfertilized soil with the insufficient nitrogen and/or phosphorous (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) might limit the residue availability for microbial growth. Organic manure treatment is thus a significant a significant control on the transformation of residue C into microbial biomass as well as the stabilization of residue C in soil. Therefore, the residue-derived C contribution to MBC could be attributed with the initial soil C and nutrient background.\u003c/p\u003e \u003c/div\u003e "},{"header":"Conclusion","content":" \u003cp\u003eIn summary, our results demonstrate that the incorporation of maize residue C into soil labile organic C pools (i.e., EOC and MBC) is strongly affected by residue type and soil fertilization. Specifically, root-derived C accumulated more in EOC and MBC than aboveground residue C in the organic-fertilized soil, but leaf-derived C accumulated more in MBC than those of root- and stem-derived C in the unfertilized soil, suggesting that root residue could lead to a greater potential labile C pool, which could constitute the primary C source for the microbial biomass and the precursor of stable SOC. This trend also indicates that the sequestration mechanisms of root \u003cem\u003evs\u003c/em\u003e. aboveground residues is regulated by soil fertilization, i.e., root-derived C may contribute more to stable SOC in the form of microbial products in the organic-fertilized soil, whereas leaf-derived C may be transformed into SOC more through the microbial synthesis in the unfertilized soil. Moreover, the contribution of residue C into EOC was greater in the unfertilized soil than that in the organic-fertilized soil, but more residue C was incorporated into MBC in the organic-fertilized soil than that in the unfertilized soil. This implies that the organic-fertilized soil should trigger a high C stabilization capacity following plant residue addition due to more microbial production, but the unfertilized soil was beneficial to promote the accumulation of plant residue in the form of EOC.\u003c/p\u003e "},{"header":"Declarations","content":" \u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis study is supported by the National Natural Science Foundation of China (41977086, 41701330, 41771328). We are thankful to Shifeng Fu for technical support with the establishment of the experiment and elemental analyses. We also thankful to Jun Cui\u0026rsquo;s suggestions of this original manuscript. Ninghui Xie would like to thank China Scholarship Council for the financial support from the visiting scholar program. We thank the anonymous reviewers for their helpful comments that significantly improved the manuscript.\u003c/p\u003e "},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAmelung W, Brodowski S, Sandhage-Hofmann A, Bol R (2008) Combining biomarker with stable isotope analyses for assessing the transformation and turnover of soil organic matter. Adv Agron 100:155-250.\u003c/li\u003e\n\u003cli\u003eAn T, Schaeffer S, Zhuang J, Radosevich M, Li S, Li H, Pei J, Wang J (2015a) Dynamics and distribution of \u003csup\u003e13\u003c/sup\u003eC-labeled straw carbon by microorganisms as affected by soil fertility levels in the Black Soil region of Northeast China. 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Plant Soil 410: 247-58.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"maize residue, soil fertilization, 13C-labeling technique, extractable organic carbon, microbial biomass carbon","lastPublishedDoi":"10.21203/rs.3.rs-341230/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-341230/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe labile organic carbon (C) pool plays a vital role in soil biogeochemical transformation and can be used as a sensitive indicator of the response of soil quality to agricultural practice. However, little is known about how residue type and soil fertilization affect the incorporation of residue C into labile organic C pools. A 360-day laboratory incubation was conducted with the addition of \u003csup\u003e13\u003c/sup\u003eC-labeled maize residues (root, stem and leaf) to unfertilized and organic-fertilized soils. A greater contribution of residue C to extractable organic C (EOC, 7.2%) was observed in the unfertilized soil than that in the organic-fertilized soil (6.0%). The contribution of residue C to microbial biomass C (MBC) was 20%-50% in the organic-fertilized soil, but only 10%-30% in the unfertilized soil. This suggests that, in organic-fertilized soil, there is accelerated transformation of residue C into microbial biomass and a higher capacity for residue C stabilization through greater, or more efficient anabolism. Moreover, the distribution of leaf C into MBC was higher than that from root and stem in the unfertilized soil, whereas more root C entered to EOC and MBC than from stem and leaf in the organic-fertilized soil. This shows that maize root can also be involved in microbial assimilation, but it depends on the initial soil nutrition. Overall, these findings deepen our understanding of the mechanisms of microbe-mediated C transformation processes, and provide relevant insights into the capture and incorporation of plant residue C into labile organic C pools driven by residue type and soil fertilization.\u003c/p\u003e","manuscriptTitle":"Effect of Residue Type on Extractable Organic and Microbial Biomass Carbon Fractions Under Long-Term Soil Fertilization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2021-03-23 15:13:44","doi":"10.21203/rs.3.rs-341230/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"14c50d3b-d7ad-4292-8bc0-c5d5a4492fb5","owner":[],"postedDate":"March 23rd, 2021","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":3156291,"name":"Geochemistry"}],"tags":[],"updatedAt":"2021-05-08T21:02:19+00:00","versionOfRecord":[],"versionCreatedAt":"2021-03-23 15:13:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-341230","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-341230","identity":"rs-341230","version":["v1"]},"buildId":"wLkW0s4AflPzk-lpfg-fK","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}