Effect of soil moisture on nematode abundance and composition is modulated by determinism in community assembly in a savanna

Effect of soil moisture on nematode abundance and composition is modulated by determinism in community assembly in a savanna | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 26 March 2025 V1 Latest version Share on Effect of soil moisture on nematode abundance and composition is modulated by determinism in community assembly in a savanna Authors : Haoran Lei , Na Lin , Jinxiu Zhang , Chunyu Hou , Chunyu Yue , Yajun Chen , and Jianping Wu 0000-0002-5784-834X [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174301400.01050346/v1 480 views 227 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Understanding how organisms adapt to drought conditions is of great importance for future ecological conservation and restoration efforts, as climate models predict planet-wide increases in the frequency of drought events. Soil nematodes play an important role in various key ecological processes and functions. However, how nematode communities respond to drought in savanna ecosystems remains largely unexplored. Here, we characterized soil nematode communities and soil properties across two seasons in plots located at four different elevations in the Yuanjiang savanna, China. We explored distributions of nematode abundance and diversity and used a null model to identify the mechanisms underlying nematode community assembly. We found that soil moisture was the primary driver of nematode abundance, with higher soil moisture directly promoting omnivore-predators diversity and shaping patterns of diversity in other nematode groups via niche divergence. Meanwhile, ammonium nitrogen influenced the diversity and abundance of plant parasite. Total phosphorus influenced bacterivore and plant parasite diversity. Furthermore, soil moisture determined the composition of soil nematode communities, and the stronger the determinism in community assembly, the closer the relationship between soil moisture and community composition and abundance. Seasonal variation in precipitation and microbial biomass carbon regulated the determinism of community assembly. Overall, our findings highlight the pivotal role of soil moisture in shaping patterns of nematode abundance and reveal the key factors influencing soil nematode community assembly in dry-hot regions. not-yet-known not-yet-known not-yet-known unknown Title: Effect of s oil moisture on nematode abundance and composition is modulated by determinism in community assembly in a savanna Abstract Understanding how organisms adapt to drought conditions is of great importance for future ecological conservation and restoration efforts, as climate models predict planet-wide increases in the frequency of drought events. Soil nematodes play an important role in various key ecological processes and functions. However, how nematode communities respond to drought in savanna ecosystems remains largely unexplored. Here, we characterized soil nematode communities and soil properties across two seasons in plots located at four different elevations in the Yuanjiang savanna, China. We explored distributions of nematode abundance and diversity and used a null model to identify the mechanisms underlying nematode community assembly. We found that soil moisture was the primary driver of nematode abundance, with higher soil moisture directly promoting omnivore-predators diversity and shaping patterns of diversity in other nematode groups via niche divergence. Meanwhile, ammonium nitrogen influenced the diversity and abundance of plant parasite. Total phosphorus influenced bacterivore and plant parasite diversity. Furthermore, soil moisture determined the composition of soil nematode communities, and the stronger the determinism in community assembly, the closer the relationship between soil moisture and community composition and abundance. Seasonal variation in precipitation and microbial biomass carbon regulated the determinism of community assembly. Overall, our findings highlight the pivotal role of soil moisture in shaping patterns of nematode abundance and reveal the key factors influencing soil nematode community assembly in dry-hot regions. Key words: Soil nematodes; Community assembly; Distribution patterns; Savanna ecosystems; Elevation gradient 1. Introduction Climate models predict that the frequency, intensity, and geographic extent of droughts will continue to increase across the globe (Masson-Delmotte et al., 2021), increasing the importance of interactions between organisms inhabiting the areas impacted by drought. The Yuanjiang dry-hot valley, located in southwestern China, is a savanna ecosystem that experiences an arid climate due to the unusual combination of subsidence airflow and the Foehn effect (Jing, 1999). Climate in the valley is also influenced by a pronounced elevation gradient, which influences local temperature, humidity, and soil properties in ways that impact the structure of biological communities (Kergunteuil et al., 2016). Previous work has shown that soil in low elevation areas in the valley exhibits the light texture, low organic matter content, and poor water retention capacity characteristic of soils in arid climates. In contrast, soil in higher elevation areas is characterized by relatively high soil moisture and organic matter content (Wang, 2021). Recent studies have found significant differences in plant community distributions across the elevation gradient in the valley (Yu et al., 2018; Wang, 2021). However, it remains unclear whether the distributions of soil biological communities – soil nematodes in particular – are similar and share the same drivers across the elevation gradient in this unique climate zone. Soil nematodes exhibit remarkable diversity and play an important role within soil faunal communities (Bardgett and van der Putten, 2014; Anthony et al., 2023). Nematodes are grouped according to their feeding habits and are classified as bacterivores (BF), fungivores (FF), plant parasites (PP), and omnivore-predators (OP) (Yeates et al., 1993). Due to these differences in feeding habits, soil nematodes occupy multiple trophic levels, thereby modulating food webs in ways that influence the entire soil biological community (de Ruiter et al., 1995; Ferris et al., 2001). For instance, soil nematode communities serve as key links in the soil food web by connecting primary consumers (bacteria and fungi) with higher trophic levels through predation (Li et al., 2014). This predatory behavior also helps regulate the structure of soil microbial communities (Ingham et al., 1985; Ferris, 2010). More importantly, soil nematode communities have a substantial impact on terrestrial ecosystem processes, such as soil carbon and nitrogen cycling (Hunt and Wall, 2002; Krumins et al., 2013). Because soil nematodes are easy to isolate from soil and are highly sensitive to environmental changes (Young and Unc, 2023), they are widely used as bioindicators of soil health. However, many studies focus only on which environmental factors affect nematode abundance and their spatial distribution patterns (Liu et al., 2019; Zhou et al., 2022; Goncharov et al., 2023; Li et al., 2023), with few studies paying attention to the processes that regulate nematode community assembly. A deeper understanding of the processes that regulate nematode community assembly is necessary for establishing a theoretical foundation for ecological restoration (Wang et al., 2023). The changes that occur in biotic and abiotic factors along ecological gradients can drive environmental filtering (Ritz and Trudgill, 1999). Therefore, studying community composition along ecological gradients can improve understanding of community assembly processes (Oliver et al., 2015). Similarly, examining the distribution of soil nematodes along an elevation gradient can improve understanding of the processes that regulate nematode community assembly. Such advances will make it possible to test whether community assembly is determined by random processes as predicted by neutral theory, such as birth, death, migration, dispersal, and colonization (Bell, 2001; Rosindell et al., 2011), or if it is driven by deterministic processes, such as environmental filtering, competition, or predation (Chase and Leibold, 2003; Gilbert, 2012). Additionally, elevation gradients provide consistent biogeographical context (Körner, 2007), thereby allowing for more robust exploration of the deterministic processes that govern community assembly. To address the research gap concerning soil nematode community in savanna ecosystems, we used a null model to determine the mechanisms of community assembly and explained the distribution patterns of nematode abundance and diversity from the perspectives of both seasonal variation and elevation gradient in Yuanjiang savanna, China. Based on historical meteorological data, both precipitation and temperature are significantly higher in September than in December (Sun et al., 2022). Numerous studies have shown that nematodes are highly sensitive to soil moisture content in arid ecosystems (Bakonyi and Nagy, 2000; Xiong et al., 2020; Bristol et al., 2023). Because nematode community responses to climate factors exhibit a “lag effect” (Kardol et al., 2010; Vandegehuchte et al., 2015), we selected October and the following January for sample collection. Additionally, existing research indicates that nematode community assembly is a deterministic process that is driven primarily by soil properties (Li et al., 2014; Moroenyane et al., 2016; Hou et al., 2022). Therefore, we hypothesized that soil nematode abundance and diversity would exhibit deterministic distribution patterns following soil moisture and elevation gradients. Additionally, we hypothesized that seasonal dynamics, particularly in precipitation and soil properties, would affect soil nematode abundance, diversity and may even alter community assembly processes. 2. Materials and methods not-yet-known not-yet-known not-yet-known unknown 2.1 Study sites The study area is located within the Yuanjiang dry-hot valley ecological station in Yuanjiang County, Yunnan Province, China. This region experiences anthropogenic disturbance, but the savanna ecosystem has been well-maintained. The dry-hot valley experiences distinct wet and dry seasons and is abundant in solar and thermal resources, with an average annual temperature of 23.7°C and annual precipitation averaging 800 mm. However, the evaporation rate is greater than 2000 mm/year, significantly higher than rainfall (Shen et al., 2010). Under these climatic conditions, the region hosts a diverse range of plant species. Dominant species in the area include Heteropogon contortus, Euphorbia royleana, and Woodfordia fruticose (Jing, 1999). 2.2 Soil sampling To investigate the distribution of nematode communities along the valley’s elevation gradient, we collected soil samples on October 2-3, 2023 and January 1-2, 2024 near the valley’s ecological station at elevations ranging between 400 and 1600 m. We established four 10m × 10m plots in randomly selected locations in relatively flat areas within each of the four transects at 400, 800, 1200, and 1600 m. Plots were separated by a distance of at least 30 m . Five samples were collected from the top 10 cm of soil in each plot, after which they were thoroughly mixed to form a single composite sample. Soil nematodes were extracted immediately from fresh soil, with the remaining soil reserved for physicochemical analysis. 2.3 Nematode extraction and identification Nematode samples were extracted from fresh soil using the Baermann funnel method (Gray, 1984). After removing roots and rocks, 50.0 g of fresh soil was transferred to a Baermann funnel, where it was mixed with pure water for nematode extraction over a period of 48 hours. Only live nematodes that remained active in the soil were extracted from the soil, after which they were quantified using a counting plate and a microscope. Our study thus considered only soil nematodes that remained active in the soil. Microscopic glass slides were prepared from each sample for nematode identification. 100 nematodes (or all nematodes in samples containing fewer than 100) were selected at random from each sample. Genus was then determined for each individual based on morphological characteristics. Both nematode counting and identification were conducted using a Leica microscope (DM 3000). Following identification, nematodes were classified into four feeding groups: BF, FF, PP, or OP (Yeates et al., 1993). Finally, Shannon diversity was calculated as an indicator of nematode diversity (Shannon, 1948). 2.4 Soil physicochemical analysis After passing soil through a 2 mm sieve, a portion was reserved to determine ammonium nitrogen (NH 4 + -N), nitrate nitrogen (NO 3 - -N), soil moisture, microbial biomass carbon (MBC), and dissolved organic carbon (DOC). Remaining soil was air-dried, with a portion finely ground and passed through a 0.85 mm sieve to measure available phosphorus (AP) and pH. Another portion of the air-dried soil was finely ground and passed through a 0.15 mm sieve to determine total nitrogen (TN), total phosphorus (TP), and soil organic carbon (SOC). NH 4 + -N, NO 3 - -N, TN, TP, and AP were analyzed using an automatic discrete chemical analyzer (Clever Chem 380, Germany). Soil moisture and pH were measured using standard methods (Dinnis, 1994). MBC was extracted using chloroform fumigation, and MBC, SOC, and DOC were analyzed using an automatic TOC analyzer (Elementar, Germany). not-yet-known not-yet-known not-yet-known unknown 2.5 Data analysis Microsoft Excel 2021 was used to organize and summarize raw data collected from the samples, and R 4.4.1 was used to perform data analysis and visualization. We used mixed-effects models to assess the effects of elevation and season on soil nematode abundance and diversity. Prior to model selection, we examined the distribution and homogeneity of variance of the response variable to ensure appropriate data characteristics. Nematode abundance was not normally distributed along the elevation gradient, so we employed a generalized linear mixed-effects model (GLMM). Conversely, nematode diversity met assumptions of normality and homogeneity of variance, allowing the use of a linear mixed-effects model (LMM). These models enabled us to separately evaluate the effects of elevation and season on nematode abundance and diversity. To account for collinearity among soil properties across the elevation gradient (Figure S1), we applied a random forest model to predict the impact of soil properties on nematode abundance and diversity. This approach can be used to identify nonlinear relationships and interaction effects, helping to mitigate the effects of collinearity (Dumitrescu et al., 2022; Rothacher and Strobl, 2023). We tested whether nematode communities varied with elevation using Bray-Curtis dissimilarity with the Adonis function (permutational MANOVA using distance matrices) in the vegan R package. To visualize differences between nematode communities, we performed non-metric multidimensional scaling (NMDS) based on Bray-Curtis dissimilarity. To determine the mechanisms underlying community assembly, we employed a null model. First, we calculated the Bray-Curtis distance to represent nematode β-diversity, as Bray-Curtis distance is highly resistant to noise and reliably reflects ecological differences between locations (Faith et al., 1987). To test whether the observed β-diversity patterns were the result of a random or ordered distribution, we constructed a null model by randomly assigning nematode abundance using three constraints (Zhang et al., 2015): (1) Species richness remained the same in both simulated and observed data from each site; (2) The frequency of species occurrence was identical between both simulated and observed data; (3) Total species abundance was consistent between simulated and observed data. 1000 null models were used to simulate β-diversity, which was then compared to observed data using the random matrix function in the Picante R package (Hou et al., 2022). Standard effect size (SES) was used to quantify β-diversity, which helped determine whether community assembly was driven by random or deterministic processes (Gotelli and McCabe, 2002). The Wilcoxon signed-rank test was used to evaluate whether SES was approximately equal to or significantly greater or less than 0, indicating the probability of a random distribution or significant species divergence or convergence, respectively. \[SES=\frac{\text{β\ diversity}_{\text{observed}}-\text{β\ diversity}_{\text{random}}}{\text{β\ diversity}_{\text{sd}}}\] where \(\text{β\ diversity}_{\text{observed}}\) represents observed β-diversity, \(\text{β\ diversity}_{\text{random}}\) represents mean β-diversity of the simulated null community, and \(\text{β\ diversity}_{\text{sd}}\) represents the standard deviation of β-diversity generated from 1,000 simulations. To investigate the pathways by which elevation and season influenced nematode community assembly, we conducted structural equation modeling (SEM) using the lavaan R package. Here, we quantified soil available nutrients as DOC, NH4+-N, NO3--N, and AP. We used principal components analyses to create multivariate indices using the first principal components axis for soil nutrients. Variation in soil nutrient content explained 50.35% of the variance associated with elevational and seasonal differences. 3. Results 3.1 Effects of elevation and season on soil properties Soil moisture increased significantly with elevation, but there were no significant differences between seasons (Figure 1A). AP decreased significantly with increasing elevation and did not vary seasonally. TP did not change significantly with elevation or season (Figure 1B). Additionally, MBC and DOC decreased significantly with elevation and exhibited seasonal differences in the 800 m plot. SOC increased significantly with elevation and did not vary seasonally (Figure 1C). NH 4 + -N increased with elevation in October, but no such trend was observed in January and we also observed notable seasonal differences in NH 4 + -N at the 800, 1200, and 1600 m plots. Neither TN nor NO 3 - -N varied with season or elevation (Figure 1D). 3.2 Patterns and drivers of nematode abundance and diversity Nematode abundance and diversity varied significantly with elevation (Table S1). The abundance of BF was significantly lower at 1200 m than at 800 m, but it exhibited an overall increase. The abundance of other nematode groups increased with elevation (Figure 2A). The abundance of PP higher in October than in January, as did the diversity of BF and PP (Figure 2B). Random forest modeling suggested that soil moisture had a significant effect on nematode abundance across groups, while soil moisture, MBC, and AP influenced OP diversity (Figure 2C). NH 4 + -N had a significant impact on PP abundance and diversity, and TP influenced PP and BF diversity (Figure 2C). Notably, the impact of all soil properties on FF diversity was relatively minor (Figure 2C). 3.3 Nematode community assembly and composition Nematode community composition varied significantly along the elevational gradient, regardless of season (Table S2). We observed that in October, the nematode community composition was closely related to soil moisture (Figure 3B), but this relationship weakened in January (Figure 3A). In both January and October, SES was significantly greater than 0 (Figure 4), indicating that community assembly was governed by deterministic processes. This resulted in species divergence, in which species tend to occupy different niches to avoid direct competition. Notably, SES values were significantly higher in October than in January ( P < 0.001), indicating that deterministic processes were more intense in October than in January. SEM results showed that increasing soil moisture promoted nematode abundance, whereas higher MBC increased the determinism of community assembly and reduced nematode diversity (Figure 5). Additionally, seasonal variation directly influenced nematode diversity and community assembly (Figure 5). 4. Discussion Our results suggest that soil moisture is the primary driver of patterns of nematode abundance along the elevational gradient in the Yuanjiang dry-hot valley, consistent with our first hypothesis. The abundance of all nematode groups increased significantly with increasing elevation and soil moisture (Figure S2), aligning with previous research demonstrating that soil nematodes are highly sensitive to variation in soil moisture (Sylvain et al., 2014; Nielsen and Ball, 2015; Xiong et al., 2020). Because nematodes live in the water films surrounding soil particles and depend on water for movement (Freckman et al., 1987; Nzogela et al., 2020), soil moisture is a crucial factor modulating nematode life processes (Song et al., 2016; Nisa et al., 2021). Thus, in this region, soil moisture determines habitat suitability for nematodes and regulates their abundance. We did not consider the impact of temperature variation along the elevation gradient, as many studies suggest that the effects of temperature are mediated by soil moisture (Blankinship et al., 2011; Zhou et al., 2022; Li et al., 2025). Contrary to our hypothesis, soil moisture did not have a significant impact on nematode diversity, except for OP. This could be because nematodes exhibit niche divergence at different elevations, enabling species to adapt to local soil moisture availability (Chesson, 2000). Our findings suggest that nematode community assembly in this region is guided by deterministic processes, which leads to niche divergence. Moreover, soil moisture niche values of nematode show that the nematodes that are dominant at higher elevations tend to require higher levels of soil moisture (Table S3). Thus, we conclude that niche divergence under variable soil moisture conditions explains why nematode diversity was not driven by soil moisture. However, because OP nematodes are larger and require greater resources and soil moisture for movement and predation, their diversity is more sensitive to changes in soil moisture and MBC (Sylvain et al., 2014; van den Hoogen et al., 2019; Lai and Kumar, 2020). AP has a significant impact on nematode community structure (Ni et al., 2024), which may alter the food chain of OP nematodes in ways that affect their diversity. Moreover, TP can alter microbial community structure (Liu et al., 2012), and BF sustain their growth and activity by preying on bacteria (Fu et al., 2005; Jiang et al., 2017). As such, TP had a significant impact on BF diversity. Additionally, soil in the Yuanjiang dry-hot valley is deficient in nitrogen and phosphorus (Liu et al., 2007), which increases plant root sensitivity to changes in the availability of these nutrients (Li et al., 2021). Variation in NH 4 + -N and TP affects plant root growth (Nacry et al., 2005; Liu and von Wirén, 2017; Bai et al., 2021), which in turn influences PP abundance and diversity. Additionally, previous studies have found that nitrogen addition can directly affect the abundance of PP (Zhou et al., 2023). In our comparison between the null model and observations of nematode communities, we found that community assembly followed a deterministic process in both October and January, with determinism being significantly higher in October than in January. This supports our second hypothesis and indicates that seasonal changes would influence community assembly. Because of the significant seasonal variation in precipitation amount and frequency (Figure S3), we suggest that increasing precipitation significantly enhances nematode dispersal and colonization. In fact, like other small passive dispersers, nematodes can easily traverse regional boundaries via flows of air and water, effectively tracking changing environmental conditions (Heino et al., 2017; Li et al., 2024). Consequently, nematodes that are adapted to high soil moisture at high elevations are more likely to colonize lower elevation areas (Pulliam, 1988; Lowe and McPeek, 2014). Therefore, when community assembly determinism was stronger, soil nematode communities were better able to track changes in soil moisture, leading to a closer relationship between soil moisture and community composition. Moreover, soil moisture demonstrated a stronger correlation with nematode abundance (Figure S4). In conclusion, our results show that the stronger the determinism in soil nematode community assembly, the better we can predict community composition based on soil moisture. In fact, previous studies have also highlighted that understanding the community assembly process is crucial for explaining changes in community composition in response to environmental changes (Schlägel et al., 2020). In addition to the influence of seasonal differences, SEM analysis revealed that increasing MBC increased the determinism of community assembly. Deterministic community assembly processes are related to environmental filtering and interactions such as competition (Chase and Leibold, 2003; Gilbert, 2012). MBC was significantly higher in October than in January, suggesting that increasing MBC intensified nematode competition, thereby increasing community assembly determinism. Previous studies have revealed positive feedbacks between BF abundance and MBC (Fu et al., 2005), and increasing BF abundance may intensify competition between BF species (Cornell et al., 1992). At the same time, consistent with the competitive exclusion principle (Hardin, 1960), higher MBC also reduces nematode diversity. 5. Conclusions Our findings suggest that soil moisture was the primary control on nematode abundance, which increased with increasing soil moisture for all groups. However, only omnivore-predators diversity was directly affected by soil moisture. Nematode diversity was primarily controlled by soil nitrogen and phosphorus. NH 4 + -N influenced both plant parasite diversity and abundance, and total phosphorus impacted bacterivores and plant parasite diversity. At the same time, soil moisture determined the composition of soil nematode communities, and the stronger the determinism in community assembly, the closer the relationship between soil moisture and community composition and abundance. In addition, MBC may have influenced community assembly by affecting nematode competition, while increased precipitation enhanced nematode dispersal and colonization, reinforcing this determinism. Our findings provide new insights to understand how nematodes are distributed along elevational gradients in savanna ecosystems, which deepens overall understanding of soil faunal diversity and community assembly under the stressful environmental conditions typical of dry-hot regions. References Anthony, M. A., Bender, S. F. and van der Heijden, M. G. A. 2023. Enumerating soil biodiversity. - Proc. Natl. Acad. Sci. USA 120: e2304663120. Bai, T., Wang, P., Ye, C. and Hu, S. 2021. Form of nitrogen input dominates N effects on root growth and soil aggregation: A meta-analysis. - Soil Biol. Biochem. 157: 108251. Bakonyi, G. and Nagy, P. 2000. Temperature- and moisture-induced changes in the structure of the nematode fauna of a semiarid grassland – patterns and mechanisms. - Glob. Change Biol. 6: 697-707. Bardgett, R. D. and van der Putten, W. H. 2014. Belowground biodiversity and ecosystem functioning. - Nature 515: 505-11. Bell, G. 2001. Neutral macroecology. - Science 293: 2413-2418. Blankinship, J. C., Niklaus, P. A. and Hungate, B. A. 2011. A meta-analysis of responses of soil biota to global change. - Oecologia 165: 553-65. Bristol, D., Hassan, K., Blankinship, J. C. and Nielsen, U. N. 2023. Responses of nematode abundances to increased and reduced rainfall under field conditions: A meta-analysis. - Ecosphere 14: e4364. Chase, J. M. and Leibold, M. A. 2003. Ecological Niches: Linking Classical and Contemporary Approaches. - University of Chicago Press, Chicago, pp. 1-20. Chesson, P. 2000. Mechanisms of maintenance of species diversity. - Annu. Rev. Ecol. Evol. Syst. 31: 343-366. Cornell, H. V., Lawton, J. H., Carroll, J., Royer, D. L. and Laundre, J. 1992. Species interactions, local and regional processes, and limits to the richness of ecological communities: a theoretical perspective. - J. Anim. Ecol. 61: 1-12. de Ruiter, P. C., Neutel, A. M. and Moore, J. C. 1995. Energetics, patterns of interaction strengths, and stability in real ecosystems. - Science 269: 1257-1260. Dinnis, E. R. 1994. Soil Science: Methods & Applications. - John Wiley and Sons, Ltd, New York, pp. 573-574. Dumitrescu, E. I., Hué, S., Hurlin, C. and Tokpavi, S. 2022. Machine learning for credit scoring: improving logistic regression with non-linear decision tree effects. - Eur. J. Oper. Res. 297: 1178-1192. Faith, D. P., Minchin, P. R. and Belbin, L. 1987. Compositional dissimilarity as a robust measure of ecological distance. - Vegetatio 69: 57-68. Ferris, H., Bongers, T. and de Goede, R. G. M. 2001. A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. - Appl. Soil Ecol. 18: 13-29. Ferris, H. 2010. Contribution of nematodes to the structure and function of the soil food web. - J. Nematol. 42: 63-7. Freckman, D. W., Whitford, W. G. and Steinberger, Y. 1987. Effect of irrigation on nematode population dynamics and activity in desert soils. - Biol. Fertil. Soils 3: 3-10. Fu, S., Ferris, H., Brown, D. and Plant, R. 2005. Does the positive feedback effect of nematodes on the biomass and activity of their bacteria prey vary with nematode species and population size? - Soil Biol. Biochem. 37: 1979-1987. Gilbert, B. 2012. Joint consequences of dispersal and niche overlap on local diversity and resource use. - J. Ecol. 100: 287-296. Goncharov, A. A., et al. 2023. A meta-analysis suggests climate change shifts structure of regional communities of soil invertebrates. - Soil Biol. Biochem. 181: 109014. Gotelli, N. J. and McCabe, D. J. 2002. Species co-occurrence: a meta-analysis of j. M. Diamond’s assembly rules model. - Ecology 83: 2091-2096. Gray, N. F. 1984. Ecology of nematophagous fungi: Comparison of the soil sprinkling method with the Baermann funnel technique in the isolation of endoparasites. - Soil Biol. Biochem. 16: 81-83. Hardin, G. 1960. The competitive exclusion principle. - Science 131: 1292-1297. Heino, J., Soininen, J., Alahuhta, J., Lappalainen, J. and Virtanen, R. 2017. Metacommunity ecology meets biogeography: effects of geographical region, spatial dynamics and environmental filtering on community structure in aquatic organisms. - Oecologia 183: 121-137. Hou, W. C., He, M. F., Qi, Y. W., Liu, T. D. and Luo, J. H. 2022. Soil nematode community assembly in a primary tropical lowland rainforest. - Front. Ecol. Evol. 10: 8. Hunt, H. W. and Wall, D. H. 2002. Modelling the effects of loss of soil biodiversity on ecosystem function. - Glob. Change Biol. 8: 33-50. Ingham, R. E., Trofymow, J. A., Ingham, E. R. and Coleman, D. C. 1985. Interactions of bacteria, fungi, and their nematode grazers: effects on nutrient cycling and plant growth. - Ecol. Monogr. 55: 119-140. Jiang, Y., Liu, M., Zhang, J., Chen, Y., Chen, X., Chen, L., Li, H., Zhang, X.-X. and Sun, B. 2017. Nematode grazing promotes bacterial community dynamics in soil at the aggregate level. - ISME J. 11: 2705-2717. Jing, Z. 1999. A phytosociological study on the semi-savanna vegetation in the dry-hot valleys of Yuanjiang River, Yunnan. - Guihaia 19: 14. Kardol, P., Cregger, M. A., Campany, C. E. and Classen, A. T. 2010. Soil ecosystem functioning under climate change: plant species and community effects. - Ecology 91: 767-781. Kergunteuil, A., Campos-Herrera, R., Sanchez-Moreno, S., Vittoz, P. and Rasmann, S. 2016. The abundance, diversity, and metabolic footprint of soil nematodes is highest in high elevation alpine grasslands. - Front. Ecol. Evol. 4: 84. Körner, C. 2007. The use of ’altitude’ in ecological research. - Trends Ecol. Evol. 22: 569-574. Krumins, J. A., et al. 2013. Soil and freshwater and marine sediment food webs: their structure and function. - Bioscience 63: 35-42. Lai, L. and Kumar, S. 2020. A global meta-analysis of livestock grazing impacts on soil properties. - Plos One 15: e0236638. Li, D., Chen, D., Hou, C., Chen, H., Zhou, Q. and Wu, J. 2025. Soil microfauna mediate multifunctionality under multilevel warming in a primary forest. - J. Anim. Ecol. 94: 58-68. Li, G. X., Wilschut, R. A., Luo, S. W., Chen, H., Wang, X. T., Du, G. Z. and Geisen, S. 2023. Nematode biomass changes along an elevational gradient are trophic group dependent but independent of body size. - Glob. Change Biol. 29: 4898–4909. Li, J. T., Li, S. P., Chen, Y. J., Jia, P., Hua, Z. S., Wang, S. L., Song, Y. S., Liao, B. and Shu, W. S. 2014. Phylogenetic structures of soil nematode communities along a successional gradient in an unreclaimed copper mine tailings site. - Soil Biol. Biochem. 77: 179-186. Li, Z., Qiu, X., Sun, Y., Liu, S., Hu, H., Xie, J., Chen, G., Xiao, Y., Tang, Y. and Tu, L. 2021. C: N:P stoichiometry responses to 10 years of nitrogen addition differ across soil components and plant organs in a subtropical Pleioblastus amarus forest. - Sci. Total Environ. 796: 148925. Li, Z., Zhu, H., García-Girón, J., Gu, S., Heino, J., Xiong, X., Yang, J., Zhao, X., Jia, Y., Xie, Z. and Zhang, J. 2024. Historical and dispersal processes drive community assembly of multiple aquatic taxa in glacierized catchments in the Qinghai-Tibet plateau. - Environ. Res. 251: 118746. Liu, F., Zhu, H., Shi, J. and Chen, X. 2007. Characteristics of plant communities and their soil fertilities in dry-hot valley of Yuanjiang county, Yunnan, China. - Chin. J. Appl. Environ. Biol. 13: 782-787. Liu, L., Gundersen, P., Zhang, T. and Mo, J. 2012. Effects of phosphorus addition on soil microbial biomass and community composition in three forest types in tropical China. - Soil Biol. Biochem. 44: 31-38. Liu, T., Hu, F. and Li, H. X. 2019. Spatial ecology of soil nematodes: Perspectives from global to micro scales. - Soil Biol. Biochem. 137: 9. Liu, Y. and von Wirén, N. 2017. Ammonium as a signal for physiological and morphological responses in plants. - J. Exp. Bot. 68: 2581-2592. Lowe, W. H. and McPeek, M. A. 2014. Is dispersal neutral? - Trends Ecol. Evol. 29: 444-450. Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L. and Gomis, M. 2021. Climate change 2021: the physical science basis. - IPCC 2: 2391. Moroenyane, I., Dong, K., Singh, D., Chimphango, S. B. M. and Adams, J. M. 2016. Deterministic processes dominate nematode community structure in the Fynbos Mediterranean heathland of South Africa. - Evol. Ecol. 30: 685-701. Nacry, P., Canivenc, G., Muller, B., Azmi, A., Van Onckelen, H., Rossignol, M. and Doumas, P. 2005. A role for auxin redistribution in the responses of the root system architecture to phosphate starvation in Arabidopsis. - Plant Physiol. 138: 2061-2074. Ni, X., Zhu, X., Feng, Q., Zhao, D., Huang, W. and Pan, F. 2024. Effect of application rates of N and P fertilizers on soil nematode community structure in mollisols. - Agronomy 14: 507. Nielsen, U. N. and Ball, B. A. 2015. Impacts of altered precipitation regimes on soil communities and biogeochemistry in arid and semi-arid ecosystems. - Glob. Change Biol. 21: 1407-1421. Nisa, R. U., Tantray, A. Y., Kouser, N., Allie, K. A., Wani, S. M., Alamri, S. A., Alyemeni, M. N., Wijaya, L. and Shah, A. A. 2021. Influence of ecological and edaphic factors on biodiversity of soil nematodes. - Saudi J. Biol. Sci. 28: 3049-3059. Nzogela, Y. B., Landschoot, S., Kihupi, A. L., Coyne, D. and Gheysen, G. 2020. Pathogenicity of the root-lesion nematode, Pratylenchus zeae, on rice genotypes under different hydro-ecologies in Tanzania. - Nematology 22: 1-13. Oliver, T. H., Heard, M. S., Isaac, N. J., Roy, D. B., Procter, D., Eigenbrod, F., Freckleton, R., Hector, A., Orme, C. D. L. and Petchey, O. L. 2015. Biodiversity and resilience of ecosystem functions. - Trends Ecol. Evol. 30: 673-684. Pulliam, H. R. 1988. Sources, sinks and population regulation. - Am. Nat. 132: 652-661. Ritz, K. and Trudgill, D. L. 1999. Utility of nematode community analysis as an integrated measure of the functional state of soils: perspectives and challenges. - Plant Soil 212: 1-11. Rosindell, J., Hubbell, S. P. and Etienne, R. S. 2011. The unified neutral theory of biodiversity and biogeography at age ten. - Trends Ecol. Evol. 26: 340-348. Rothacher, Y. and Strobl, C. 2023. Identifying informative predictor variables with random forests. - J. Educ. Behav. Stat. 49: 595-629. Shannon, C. E. 1948. A mathematical theory of communication. - Bell Syst. Tech. J. 27: 379-423. Shen, R., Zhang, J., He, B., Li, F., Zhang, Z., Zhou, R. and Ou, X. 2010. The structure characteristic and analysis on similarity of grassland community in dry-hot valley of Yuanjiang River. - Ecol. Environ. 19: 2821-2825. Song, M., Li, X., Jing, S., Lei, L., Wang, J. and Wan, S. 2016. Responses of soil nematodes to water and nitrogen additions in an old-field grassland. - Appl. Soil Ecol. 102: 53-60. Sun, C., Yang, D., Song, Q., Chen, A., Wen, G., Zhang, S., Zhang, J., Duan, X. and Jin, Y. 2022. A dataset of meteorological observations at Yuanjiang Savanna Ecosystem Research Station, Yunnan Province (2011-2020). - China Sci. Data 7: 2096-2223. Sylvain, Z. A., Wall, D. H., Cherwin, K. L., Peters, D. P. C., Reichmann, L. G. and Sala, O. E. 2014. Soil animal responses to moisture availability are largely scale, not ecosystem dependent: insight from a cross-site study. - Glob. Ecol. Biogeogr. 20: 2631-2643. van den Hoogen, J., et al. 2019. Soil nematode abundance and functional group composition at a global scale. - Nature 572: 194-198. Vandegehuchte, M. L., Sylvain, Z. A., Reichmann, L. G., de Tomasel, C. M., Nielsen, U. N., Wall, D. H. and Sala, O. E. 2015. Responses of a desert nematode community to changes in water availability. - Ecosphere 6: 44. Wang, J. 2021. Characteristics of foehn and its influence on vegetation in Yuanjiang Dry-Hot Valley, Yunnan Province. - PhD thesis, Yunnan University, China. Wang, W., Sun, Z., Mishra, S., Xia, S., Lin, L. and Yang, X. 2023. Body size determines multitrophic soil microbiota community assembly associated with soil and plant attributes in a tropical seasonal rainforest. - Mol. Ecol. 32: 6294-6303. Xiong, D., Wei, C., Wubs, E. R. J., Veen, G. F., Liang, W., Wang, X., Li, Q., Van der Putten, W. H. and Han, X. 2020. Nonlinear responses of soil nematode community composition to increasing aridity. - Glob. Ecol. Biogeogr. 29: 117-126. Yeates, G. W., Bongers, T., De Goede, R. G., Freckman, D. W. and Georgieva, S. S. 1993. Feeding habits in soil nematode families and genera-an outline for soil ecologists. - J. Nematol. 25: 315-31. Young, E. H. and Unc, A. 2023. A review of nematodes as biological indicators of sustainable functioning for northern soils undergoing land-use conversion. - Appl. Soil Ecol. 183: 104762. Yu, J., Si, H., Wu, X., Zhang, Y., Su, W. and Zhou, R. 2018. Characteristics of plant communities in Yuanmou dry-hot valley under different elevation gradients. - Ecol. Environ. Sci. 27: 2017-2022. Zhang, H., Qi, W., John, R., Wang, W., Song, F. and Zhou, S. 2015. Using functional trait diversity to evaluate the contribution of multiple ecological processes to community assembly during succession. - Ecography 38: 1176-1186. Zhou, J., Wu, J., Huang, J., Sheng, X., Dou, X. and Lu, M. 2022. A synthesis of soil nematode responses to global change factors. - Soil Biol. Biochem. 165: 108538. Zhou, Q., Wang, X., Wu, Y., Chen, Z., Li, D., Shao, Y. and Wu, J. 2023. Contrasting responses of soil nematode trophic groups to long-term nitrogen addition. - Ecosystems 26: 893-908. Figure legends Figure 1. Soil properties along an elevational gradient in January and October. Data are presented with standard error bars. Different letters above columns indicate values that are significantly different between treatments at the P < 0.05 level (HSD’s test). Figure 2. Patterns (A-elevation; B–season) and drivers (C) of nematode abundance and diversity. In B, * indicates that season had a significant effect on nematode abundance and diversity (elevation treated as a random factor). In C, * and ** indicate significance at the P < 0.05 and P < 0.01 levels, respectively. Bacterivores (BF), fungivores (FF), plant parasites (PP), and omnivore-predators (OP). Figure 3. Non-metric Multidimensional Scaling (NMDS) of nematode communities in January (A) and October (B). Clustering is based on Bray-Curtis similarity, with resulting 2D stress values for the best solution of 0.142 in January and 0.114 in October. Figure 4. Distribution of β-diversity SES. SES values that are significantly greater than, smaller than, or approaching zero indicate significant species divergence, significant species convergence, or random distribution, respectively. The center line within box plots indicates the median; top and bottom boundary lines indicate the 25 th and 75 th percentiles, respectively; and the error bars represent the 10 th and 90 th percentiles of SES at each spatial scale. Figure 5. Structural equation model (SEM) examining the direct and indirect effects of elevation and season on nematode community assembly. Black and red lines indicate positive and negative effects, respectively. Line thickness indicates the strength of significant path coefficients, and gray lines indicate non-significant paths. Values associated with arrows are standardized path coefficients. r 2 values linked with response variables indicate the proportion of variation explained by relationships with other variables. Chisq = 4.763, df = 5.00, P = 0.446, gfi = 0.986, cfi = 1.000, rmr = 0.034, srmr = 0.035, rmsea < 0.001. Information & Authors Information Version history V1 Version 1 26 March 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords community assembly distribution patterns elevation gradient savanna ecosystems soil nematodes Authors Affiliations Haoran Lei Yunnan University View all articles by this author Na Lin Yunnan University View all articles by this author Jinxiu Zhang Yunnan University View all articles by this author Chunyu Hou Yunnan University View all articles by this author Chunyu Yue Yunnan University View all articles by this author Yajun Chen Xishuangbanna Tropical Botanical Garden CAS Key Laboratory of Tropical Forest Ecology View all articles by this author Jianping Wu 0000-0002-5784-834X [email protected] Yunnan University View all articles by this author Metrics & Citations Metrics Article Usage 480 views 227 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Haoran Lei, Na Lin, Jinxiu Zhang, et al. Effect of soil moisture on nematode abundance and composition is modulated by determinism in community assembly in a savanna. Authorea . 26 March 2025. DOI: https://doi.org/10.22541/au.174301400.01050346/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . Format Please select one from the list RIS (ProCite, Reference Manager) EndNote BibTex Medlars RefWorks Direct import Tips for downloading citations document.getElementById('citMgrHelpLink').addEventListener('click', function() { popupHelp(this.href); return false; }); $(".js__slcInclude").on("change", function(e){ if ($(this).val() == 'refworks') $('#direct').prop("checked", false); $('#direct').prop("disabled", ($(this).val() == 'refworks')); }); Cited by Loading... View Options View options PDF View PDF Figures Tables Media Share Share Share article link Copy Link Copied! Copying failed. Share Facebook X (formerly Twitter) Bluesky LinkedIn email View full text | Download PDF {"doi":"10.22541/au.174301400.01050346/v1","type":"Article"} Now Reading: Share Figures Tables Close figure viewer Back to article Figure title goes here Change zoom level Go to figure location within the article Download figure Toggle share panel Toggle share panel Share Toggle information panel Toggle information panel Go to previous graphic Go to next graphic Go to previous table Go to next table All figures All tables View all material View all material xrefBack.goTo xrefBack.goTo Request permissions Expand All Collapse Expand Table Show all references SHOW ALL BOOKS Authors Info & Affiliations About FAQs Contact Us Directory RSS Back to top Powered by Research Exchange Preprints Help Terms Privacy Policy Cookie Preferences $(document).ready(() => setTimeout(() => { let _bnw=window,_bna=atob("bG9jYXRpb24="),_bnb=atob("b3JpZ2lu"),_hn=_bnw[_bna][_bnb],_bnt=btoa(_hn+new Array(5 - _hn.length % 4).join(" ")); $.get("/resource/lodash?t="+_bnt); },4000)); (function(){function c(){var b=a.contentDocument||a.contentWindow.document;if(b){var d=b.createElement('script');d.innerHTML="window.__CF$cv$params={r:'a0030531afdd4193',t:'MTc3OTUyODM5OQ=='};var a=document.createElement('script');a.src='/cdn-cgi/challenge-platform/scripts/jsd/main.js';document.getElementsByTagName('head')[0].appendChild(a);";b.getElementsByTagName('head')[0].appendChild(d)}}if(document.body){var a=document.createElement('iframe');a.height=1;a.width=1;a.style.position='absolute';a.style.top=0;a.style.left=0;a.style.border='none';a.style.visibility='hidden';document.body.appendChild(a);if('loading'!==document.readyState)c();else if(window.addEventListener)document.addEventListener('DOMContentLoaded',c);else{var e=document.onreadystatechange||function(){};document.onreadystatechange=function(b){e(b);'loading'!==document.readyState&&(document.onreadystatechange=e,c())}}}})();