Urbanization Promotes Topsoil Black Carbon Accumulation: A Meta-analysis

Urbanization Promotes Topsoil Black Carbon Accumulation: A Meta-analysis | 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 Search Search ADVANCED SEARCH SCROLL Land Degradation & Development This is a preprint and has not been peer reviewed. Data may be preliminary. 13 August 2025 V1 Latest version Share on Urbanization Promotes Topsoil Black Carbon Accumulation: A Meta-analysis Authors : Yu Zhao , Bingbing Li , Zhouxinnan XU , Zhiheng Song , Songyi Huang , and Min Wang 0000-0002-6896-2375 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175509204.46663144/v1 Published Land Degradation & Development Version of record Peer review timeline 276 views 138 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Accelerated urbanization highlights the significant role of urban soil black carbon (BC), a key component of soil organic carbon, for ecosystem function and human health. This meta-analysis systematically synthesized data from 54 published studies encompassing 4,548 sampling sites across 40 Chinese cities, supplemented by targeted field sampling to investigate the distribution characteristics, primary sources, and influencing factors of soil BC in China’s urban environments. Following rigorous screening, standardization, and outlier removal, correlation analysis and multivariate statistics were applied. Results revealed an average urban topsoil BC content of 6.70 ± 5.34 g/kg, exhibiting significant spatial heterogeneity: levels were higher in eastern compared to the western regions, and in northern relative to the southern cities. Fossil fuel combustion (primarily from vehicle emissions and industrial coal burning) was the dominant source, while iomass burning constituted the secondary source, with notable local contributions from urban expansion and straw burning. Further analysis indicated that higher precipitation (among natural factors) in the southern regions promotes BC migration, contributing to lower observed concentrations. Anthropogenic factors exerted a stronger influence: cities with greater urbanization levels and higher energy consumption exhibited significantly elevated BC inputs. This study comprehensively elucidates the distribution patterns and source contributions of BC in China’s urban soils. The findings provide crucial scientific support for urban environmental governance and soil quality improvement strategies during ongoing urbanization, contributing to achieving balanced urban ecosystems and promoting sustainable urban development. Title page Urbanization Promotes Topsoil Black Carbon Accumulation: A Meta-analysis Yu Zhao a ，Bingbing Li a ，Zhouxinnan XU a ,Zhiheng Song a ,Songyi Huang a , Min Wang a, * a College of Horticulture and Landscape Architecture, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China; [email protected] (Y. Z.); [email protected] (BB. L.); [email protected] (ZXN. X.); [email protected] (ZH.S); [email protected] (SY. H.) * Correspondence: [email protected] ;， Abstract Accelerated urbanization highlights the significant role of urban soil black carbon (BC), a key component of soil organic carbon, for ecosystem function and human health. This meta-analysis systematically synthesized data from 54 published studies encompassing 4,548 sampling sites across 40 Chinese cities, supplemented by targeted field sampling to investigate the distribution characteristics, primary sources, and influencing factors of soil BC in China’s urban environments. Following rigorous screening, standardization, and outlier removal, correlation analysis and multivariate statistics were applied. Results revealed an average urban topsoil BC content of 6.70 ± 5.34 g/kg, exhibiting significant spatial heterogeneity: levels were higher in eastern compared to the western regions, and in northern relative to the southern cities. Fossil fuel combustion (primarily from vehicle emissions and industrial coal burning) was the dominant source, while iomass burning constituted the secondary source, with notable local contributions from urban expansion and straw burning. Further analysis indicated that higher precipitation (among natural factors) in the southern regions promotes BC migration, contributing to lower observed concentrations. Anthropogenic factors exerted a stronger influence: cities with greater urbanization levels and higher energy consumption exhibited significantly elevated BC inputs. This study comprehensively elucidates the distribution patterns and source contributions of BC in China’s urban soils. The findings provide crucial scientific support for urban environmental governance and soil quality improvement strategies during ongoing urbanization, contributing to achieving balanced urban ecosystems and promoting sustainable urban development. Key words: urbanization; urban soil; black carbon; meta-analysis Main Text Introduction 1.1 Urbanization Under the ”Dual Carbon” Strategy To address global climate change and promote ecological civilization construction and high-quality development, China proposed the ”Dual Carbon” goal at the 75th UN General Assembly in 2020: ”Peak CO 2 emissions by 2030 and achieve carbon neutrality by 2060” (Chen Y., 2021). Urbanization and socio-economic activities are major sources of carbon emissions, rendering their management critical for achieving China’s ”Dual Carbon” targets. Soils constitute the largest organic carbon pool in terrestrial ecosystems, storing approximately twice as much carbon as the atmospheric pool and three times that of the plant carbon pool (Schlesinger, 1977). Even minor changes in soil carbon stocks can significantly alter atmospheric CO 2 concentrations, thereby impacting global climate change (Chen M. &., 2022).Black carbon (BC) is a carbonaceous compound formed through the incomplete combustion of biomass and fossil fuels [4 (Kuhlbusch, 1998). Most BC produced from combustion is directly deposited into soils (Liu D. J., 2019), making it a significant component of the soil carbon pool (Schmidt, 2001) (Edmondson, 2015). BC exhibits distinct environmental behaviors and effects across different environmental media. Estimates suggest that approximately 0.05–0.2 Pg (1 Pg = 10¹⁵ g) of BC is deposited into soils annually, contributing substantially to the soil carbon reservoir (Kuhlbusch, 1998) (Masiello, 1998). In descending order of contribution, the primary sources of soil BC comprise: natural wildfires, agricultural activities, fossil fuel combustion, and vehicle emissions (Liu L. Y., 2017). BC exhibits strong oxidation resistance, enabling long-term carbon sequestration within the geosphere by capturing carbon from the biosphere-atmosphere carbon cycle. This mechanism significantly mitigates the greenhouse effect through reducing atmospheric greenhouse gas concentrations (Weng, 2022). Owing to its high chemical inertness and porous structure, BC enhances soil organic matter content, improves soil fertility, and optimizes soil structure (DeLuca, 2009) (Luan, 2011). Furthermore, studies indicate that BC may constitute a portion of the unresolved ”missing carbon” in the global carbon cycle and potentially function as an atmospheric CO₂ sink (Druffel, 2004) (Everett, 2022). Consequently, BC is recognized as a critical carbon sink in the global carbon pool, representing a stable, inert fraction of soil organic carbon. These properties hold profound implications for soil carbon stabilization and carbon neutrality strategies (Kopecký, 2021) (Zhang, 2022). 1.2 Research on Urban Soil Black Carbon Rapid urbanization has markedly elevated anthropogenic BC emissions,primarily driven by intensified industrial and agricultural production, fossil fuel combustion, and vehicle emissions (Edmondson, 2015) (Jacobson, 2005). A substantial portion of this BC is ultimately deposited into urban and peri-urban soils through direct or indirect pathways (Pickett, 2009) (Luo, 2012). Variations in human activity intensity at different urbanization levels alter the sources and proportions of urban soil BC, leading to increasingly complex distribution patterns and characteristics. Research confirms that urban topsoil BC content is closely correlated with anthropogenic intensity (Gautam, 2020) (Li, 2019), exhibiting significantly higher concentrations compared to natural soils (e.g., deserts and farmlands) (Hamilton, 2013). Urban expansion drives alterations to natural landscapes and land-use patterns, establishing distinct functional zones categorized as: (i) semi-natural areas (e.g., green infrastructure, recreational zones, and suburbs) and (ii) fully artificial environments (e.g., industrial districts, residential areas, and road traffic zones). These functional differences further shape the spatial distribution of urban soil BC (Skjemstad, 2002) (Ansley, 2006) (Dai, 2005) (Gatari, 2003) (Rumpel, 2006) (Yin, 2009). Carbonaceous particles from fossil fuel combustion and vehicle emissions remain suspended in the atmosphere before depositing onto soils via dry/wet sedimentation—constituting the primary BC source in urban systems (Liu L. Y., 2017). Existing research demonstrates significant variations in soil BC content across urban functional zones. For instance, industrial areas and roadside soils exhibit markedly higher BC levels than other regions (Wang Q. L., 2014) (Vasenev, 2018), suggesting that industrial activities and vehicular emissions are key drivers of urban soil BC accumulation (Wang X. S., 2010).Although numerous studies have investigated soil BC, in natural ecosystems (e.g., forests, farmlands, and deserts) urban soils—which are strongly influenced by anthropogenic activities—remain relatively understudied (Coppola, 2018). In China, existing urban soil BC investigations have primarily concentrated on historical industrial centers in northern regions (Zong, 2016) (Sun, 2022) (Liu X. Z., 2022) and eastern metropolises such as Shanghai and Nanjing (Wang X. S., 2010) (He. Y, 2009), while studies from other urban areas remain scarce. Traditional literature reviews in this field offer only subjective, qualitative perspectives, and lack the capacity to for scientific quantification. Conversely, meta-analysis provides a robust approach to address specific ecological questions by synthesizing datasets from multiple studies with shared themes and objectives, thereby extracting generalized scientific insights under defined conditions (Peng, 1999) (Verhulst, 1997).A critical knowledge gap persists regarding BC accumulation in rapidly urbanizing regions and anthropogenically impacted regions, which hinders comprehensive cross-regional comparisons in China. Studies on typical large Chinese cities remain particularly scarce, especially given the notable differences in production/lifestyle patterns—and consequently BC sources—between climatically distinct northern/southern regions. Furthermore, comparative analyses of soil BC in typical natural versus urban environments are still lacking. Materials and methods 2.1 Meta-analysis Meta-analysis has emerged as a widely adopted systematic review method in ecological research in recent years. This quantitative approach synthesizes findings from multiple studies addressing identical research question to provide a statistically robust average effect size or association strength, thereby offering more precise conclusions to scientific inquiries than individual studies (Peng, 1999) (Verhulst, 1997) (Castro-Díez, 2013).Particularly valuable when dealing with divergent results caused by methodological variations, meta-analysis provides comprehensive statistical integration of multiple studies. This capability overcomes the inherent limitations of traditional literature reviews that can only offer subjective and qualitative conclusions (Liu H. H., 2015). Since its introduction to China’s ecological research by Peng et al (1998) (Guo, 2009), this methodology has gained extensive application in domestic ecological studies. 2.2 Data Collection Literature retrieval was conducted in Web of Science, PubMed, Wanfang Data, and CNKI databases using the keywords ”black carbon*soil” and ”urbanization.” To avoid duplication, publications identified across multiple sources were included only once. Data were extracted from figures and tables in the selected literature: tabular data were directly obtained, while graphical data were extracted using the GetData Graph Digitizer software. The inclusion criteria for literature screening were as follows:firstly soils with direct measurements of black carbon (BC) or at least reported organic carbon (OC) content; secondly studies that provided the latitude and longitude of sampling sites; thirdly only topsoil (0–30 cm) data were included, excluding subsoil or litter layer data; lastly studies focusing on marine/lacustrine sediments or atmospheric deposition of black carbon were excluded.From 54 eligible studies, we extracted 4,548 data points and their corresponding urban environmental variables for each sampling location. These variables included: city name, sampling year, climate type, longitude, latitude, mean annual temperature (MAT), mean annual precipitation (MAP), soil black carbon content, soil organic carbon (SOC) content. Urbanization metrics were also complied, including population density, industrial sector proportion, urban built-up area, road network density, green space ratio within built-up areas, cultivated land area. All soil data were restricted to the topsoil layer (0-30 cm). Figure 1 PRISMA Flow Diagram 2.3 Data Calculation In this study, soils from suburban areas (low urbanization intensity) were designated as the control group, while soils from urban areas (high urbanization intensity) served as the treatment group. For meta-analysis, the following parameters need to be extracted: mean values (Xc, Xt), standard deviations (Sc, St), and sample sizes (Nc, Nt) for both control and treatment groups. Among various effect size metrics available for meta-analysis, this study adopted the response ratio (lnRR) developed by Hedges (1999) (Gurevitch, 2001) due to its superior adaptability. The effect size calculation formula is as follows: The variance calculation formula for the effect size lnRR is: 2.4 Statistical Analysis Data entry was performed using Excel 2007. Spatial distribution maps of urban soil BC were plotted with ArcGIS 10.7. Integrated analysis of the selected data was conducted using mixed-effects models via the openmee software and R (v 4.4.3; http://www.r-project.org). Forest plots of effect sizes were generated using R packages metafor and ggplot2 , and the relative importance of environmental factors was calculated. Furthermore, meta-regression analysis was performed with the metafor package to evaluate the influence levels of climatic factors, population density, industrial proportion, urban built-up area, urban road density, green space ratio in built-up areas, and cultivated land area on soil BC concentration. Results 3.1 Spatial Distribution of Urban Soil Black Carbon The average BC content in China’s urban soils was 6.70 ± 5.34 g/kg, exhibiting significant spatial variability (Figure 1). In east-west gradient, higher BC content in eastern regions versus western regions, with key industrial cities such as Xi’an and Lanzhou exhibiting relatively high BC levels. Taking Shanghai in the east and the Qinghai-Tibet Plateau region in the west as examples, Shanghai recorded a BC content of 6.26 g/kg, whereas the Qinghai-Tibet Plateau region had only 2.66 g/kg. In north-south contrast, northern cities had higher soil BC content than southern cities, with 9.09 g/kg in northern cities versus 5.89 g/kg in southern cities. Spatial distribution maps indicated a general increasing trend of BC content from inland western regions to coastal eastern areas, and from southern to northern regions. Figure 2 Spatial Distribution of Black Carbon in Urban Soils Across China Based on a meta-analysis of 54 studies on BC content in urban soils of China, the results of the effect size natural logarithm of the response ratio for urban vs. suburban soils (Fig 2) showed a pooled effect size of 0.573 (95% CI: 0.405, 0.740). The confidence interval does not include zero, indicating a statistically significant effect. According to the results, 87% of the studies reported positive effects, while only 7 studies exhibited negative or neutral effects—likely due to variations in experimental methods or uneven sampling distribution. Using the response ratio formula lnRR=ln (urban BC/suburban BC), the pooled effect size was converted to a percentage of 77.3%, indicating that under different urbanization contexts, the BC content in the topsoil of urban areas is, on average, significantly higher than that in suburban areas by 77.3%. Figure 3. Effect sizes (lnRR) of BC content in urban vs. suburban soils across Chinese cities. Red dots indicate statistically significant positive effects (urban > suburban), while blue dots represent non-significant or negative effects (urban ≤ suburban). 3.2 Subgroup and Meta-regression Analyses Based on Natural and Urbanization Factors The soil BC content reported in the 54 studies exhibited considerable heterogeneity. To further clarify the sources of these differences and the extent of urbanization’s influence on soil BC, explanatory variables were introduced to investigate the sources of heterogeneity. Subgroup analyses based on natural and urbanization factors were conducted. The results of the subgroup analysis by climate type (Fig 3) indicated that studies in cities dominated by temperate monsoon climates showed higher heterogeneity in soil BC content. Cities with annual precipitation between 500–1000 mm and mean annual temperatures between 0–10°C also exhibited higher heterogeneity. These patterns likely due to the significant longitudinal variation among temperate zone cities, large seasonal fluctuations in precipitation and temperature, and substantial differences in ecological environments. Among the 54 studies, results from cities characterized by low industrial levels, small built-up areas, and high proportions of cultivated land showed higher heterogeneity. This suggests that cities with lower urbanization levels may be subject to greater influence from other anthropogenic activities. Conversely, studies in cities with higher industrial levels, larger built-up areas, and higher road density showed high consistency. Therefore, findings on influencing factors from highly urbanized cities are more credible. Furthermore, differences in geographical location, climatic conditions, and green space ratio among cities were found to significantly influence the accumulation of soil BC, leading to considerable variation in BC content. Figure 4. Subgroup Analysis by: Region、Climate type、Annual precipitation、Average annual temperature、Industry level、Road density、Population density、Cultivated land area、Urban built-up area footprint、Green space ratio in built-up areas To further investigate the factors driving heterogeneity in urban soil BC content, effect size values were used to conduct meta-regression analyses on natural factors and urbanization factors separately. Annual precipitation, mean annual temperature, and green space ratio demonstrated negative correlation with the effect size of urban soil BC (Fig 4a-c). Conversely, urban built-up area (Fig 4f), industrial level (Fig 4e), and road density (Fig 4g) showed significant positive correlations. Comparative analysis of correlation coefficients (R) revealed that industrial level ( R IL = 0.27 , P < 0.05 ), road density ( R RD = 0.19, P < 0.05 ), and annual precipitation ( R AP = -0.31, P < 0.05 ) exhibited significant and strong correlations. Figure 5. Regression Analysis of Effect Size of Urban-Suburban BC against: Annual Precipitation、Average Annual Temperature、Industry Level、Road Density、Population Density、Cultivated Land Area、Urban Built-up Area Footprint、Green Space Ratio in Built-up Areas 3.3 Sensitivity Analysis and Publication Bias Assessment of Individual Studies To further assess the reliability of the analytical results, the heterogeneity, error, and bias within the study samples included in the meta-analysis of urban soil BC) content across different cities were analyzed. Heterogeneity between studies was evaluated using Cochrane’s Q test and the I² statistic. The results showed a Cochrane’s Q value of 1895.36 (df = 53, p < 0.001) and an I² = 98.143%, indicating significant heterogeneity among the studies. Sensitivity analysis revealed that certain studies exerted a minor influence on the overall results owing to uneven distribution of sampling points and methodological discrepancies in BC detection. Following the stepwise removal of these individual studies, heterogeneity decreased, while the overall results remained stable. Publication bias was assessed using the trim-and-fill funnel plot method. The results indicated no significant publication bias, suggesting that the observed heterogeneity among studies likely stems from diverse influencing factors. In conclusion, these findings suggest that the results of this meta-analysis are robust. Figure 6. Sensitivity Analysis Plot Figure 7. Publication Bias Funnel Plot Discussion 4.1 Significant Regional Variation in Urban Topsoil BC Content The spatial distribution of topsoil BC in Chinese cities exhibits pronounced heterogeneity along east-west and north-south gradients. This spatial pattern primarily arises from the combined effects of regional natural environments and socioeconomic activities. Western China, characterized by vast land area, sparse population, and slower urban development, features mountainous grasslands primarily utilized for agricultural cultivation and possesses a relatively simple industrial structure. Concurrently, the arid climate and low precipitation levels in the west hinder the transport and deposition of BC. Consequently, soil BC in this region originates predominantly from incomplete biomass combustion (e.g., crop residue burning and fuelwood use), resulting in a topsoil BC content of 1.91 ± 1.54 g/kg. Examples include the Qinghai-Tibet Plateau and the Qinghai Lake Basin (Liao, 2017). In contrast, Eastern Coastal China, marked by high-intensity industrialization (secondary industry contribution >40%) and megacity clusters (e.g., Yangtze River Delta, Pearl River Delta, Beijing-Tianjin-Hebei), forms hotspots of anthropogenic emissions (He Y. T., 2016). These regions consume 1.5 to 2.5 billion tons of coal annually and account for 62% of China’s vehicle fleet. This leads to fossil fuel combustion as the predominant source of soil BC inputs. Furthermore, monsoon-driven atmospheric deposition enhances BC accumulation in soils through aerosol precipitation. Topsoil BC contents in industrial zones of cities like Shanghai and Guangzhou reach 6.29 ± 2.84 g/kg (Xu, 2014) (Min.W, 2022) (Zhu, 2016). As illustrated in Figure 8, BC content exhibits significant differences across climatic zones, with notably higher concentrations observed in monsoon climate regions compared to other climatic areas. Figure 8. BC Content in Different Regions and Climatic Zones of China 4.2 Synergistic Effects of Natural and Urbanization Factors on Soil BC Accumulation Precipitation exerts a significant negative influence on soil BC content. In Southern China, where annual precipitation typically exceeds 1000 mm, abundant rainfall generates surface runoff that mobilizes and transports BC away from the soil, promoting BC migration and reducing soil BC content. Conversely, Northern China receives lower annual precipitation (400–800 mm), promoting BC persistence in soils in soils and resulting in relatively higher accumulation (Wu, 2024). The identified climate regulation mechanism (enhanced leaching at precipitation >1000 mm) applies equally to tropical cities (e.g., Bangkok, MAP=1400 mm; (Bird, 1999)). In contrast, temperate cities (e.g., Berlin, MAP=580 mm; (Lorenz, 2006)) exhibit industrial drivers as predominant. This reveals the interactive dynamics between urbanization stage and climate zone.Temperature also indirectly affects soil BC dynamic. Bird et al. found BC content ranging from 3% to 7% in Laos (Bird, 1999). This is attributed to the region’s tropical location and hot, humid conditions, which facilitate the decomposition and mineralization of soil organic matter (SOM), consequently influencing the quantity and quality of total OM to which BC contributes. Higher temperatures accelerate microbial activity, promoting the decomposition and transformation of soil organic carbon (SOC). Conversely, lower temperatures suppress microbial activity, potentially affecting BC stability and accumulation processes (Smirnova, 2025). Notably, research on temperature’s specific impact on urban soil BC remains limited and warrants further investigation (Hu, 2023).Within the urbanization process, anthropogenic activitites are paramount drivers of soil BC accumulation. Industrial activities and vehicular exhaust emissions constitute the primary influencing factors (He Y. Z., 2007). Fossil fuel combustion contributes 57% of soil BC, with vehicle emissions being the dominant source (70.5%), followed by industrial coal combustion (31.4%). Energy consumption driven by industrial development, particularly the combustion of fossil fuels like coal and oil, represents the major BC source (Bladon, 2024). Rapid urban transportation growth and increasing vehicle traffic lead to substantial BC deposition from exhaust emissions into the soil (Zhu, 2016). Furthermore, activities such as construction dust generation and waste disposal during urban development also contribute to soil BC accumulation. Among urbanization indicators, population density (35.2%), built-up area expansion (23.1%), and cultivated land area (18.6%) exhibit positive correlations with BC accumulation. Conversely, green space ratio in built-up areas shows a negative correlation with soil BC accumulation. Supporting these findings, Hamilton et al. discovered significantly different BC contents in urban, agricultural, and desert soils of central Arizona, USA, with urban environments containing BC as high as 7.8% (Hamilton, 2008). Lorenz et al. investigated BC in soils of different functional zones (railways, parks, gardens) in Stuttgart, Germany, finding higher soil BC content in high population density areas like parks (Lorenz, 2006). These studies align with our results, demonstrating the substantial impact of anthropogenic activities on soil BC accumulation. Under the influence of monsoon climate as a natural factor, complex urbanization processes synergistically promote BC accumulation in topsoil. Conclusions 5.1 Research Conclusions Urban topsoil BC contents across China average 6.70 ± 5.34 g/kg, exhibiting a distinct spatial pattern characterized by elevated levels in the western and northern regions relative to eastern and southern areas. The BC content in Western China (2.06 ± 1.44 g/kg) is significantly lower than that in Eastern industrial regions (6.43 ± 3.35 g/kg). Furthermore, the mean BC content in the Northern heating zone (8.78 ± 7.37 g/kg) is 1.46 times that of the South (6.03 ± 3.38 g/kg). This spatial heterogeneity results from the synergistic interaction of regional natural environments and socioeconomic development activities. The findings confirm that differences in energy structure and climatic conditions collectively shape the spatial distribution of soil BC.Fossil fuel combustion constitutes the primary source of urban soil BC, with vehicular exhaust emissions (70.5%) and industrial coal burning (31.4%) representing the highest contributing sources; biomass combustion is a secondary source. Urbanization indicators, notably population density and built-up area footprint, exhibit significant positive associations with soil BC content. In densely populated areas, intensive vehicle use, concentrated heating energy consumption, and frequent anthropogenic disturbances directly increase BC emissions and soil deposition. Expansion of built-up areas drives the dispersion of industrial pollution, extension of transportation networks, and intensification of construction activities, promoting BC enrichment in the topsoil layer (0-30 cm). Urban greening offers a mitigating effect on soil BC accumulation. This manifests through: interception of atmospheric particulates by vegetation foliage, dilution of BC concentration via the plant carbon sink function, enhanced microbial degradation facilitated by root systems, suppression of secondary dispersion through microclimate regulation. Consequently, BC content in green space soils remains lower than in commercial zones and transportation hubs. In summary, anthropogenic activities exert a substantial impact on soil BC accumulation. Complex urbanization processes synergistically promoted BC enrichment in urban topsoils. Vegetation interception of atmospheric black carbon (BC) deposition in green spaces empirically supports the UN Decade on Ecosystem Restoration (2021-2030). Incorporating urban green-space carbon sequestration into Nationally Determined Contributions (NDCs) is recommended to advance carbon neutrality goals.Precipitation is a key natural factor regulating the spatial heterogeneity of soil BC, exhibiting a significant negative correlation. In southern regions with high precipitation (> 1000 mm/yr), intense surface runoff generates hydrological transport of BC, directly reducing topsoil accumulation. Conversely, under low- precipitation conditions (400–800 mm/yr) typical of northern zones, the retention effect of BC becomes significant, promoting in-situ accumulation.Temperature also serves as a crucial natural factor governing the spatial heterogeneity of soil BC, showing a significant negative correlation. The indirect effects of temperature warrant attention: higher environmental temperatures may accelerate microbial metabolic activity in soils, promoting the mineralization and transformation of certain degradable BC fractions, thereby affecting BC stability (Smirnova, 2025). However, quantitative research on temperature’s influence on urban soil BC turnover remains scarce. Future investigations require integrated approaches combining thermodynamic models with microbiomics techniques to elucidate underlying mechanisms (Feng, 2024). 5.2 Study Limitations This research primarily relies on data from published literature for meta-analysis, which may suffer from issues of underrepresentation—particularly for small-to-medium cities and remote regions with limited research efforts, such as Southwestern China andXinjiang Uygur Autonomous Region. Additionally, variations in research methodologies and detection standards across different studies could have introduced some degree of uncertainty into the results. Furthermore, there remains insufficient in-depth exploration of the long-term dynamic changes of BC in soils and its interactions with other soil components. Acknowledgements Funding: This study was supported by the Guangdong Basic and Applied Basic Research Foundation [grant numbers: 2023A1515110793] and the 2025 College Students’ Innovation Training Program Project [grant numbers: 202511347024]. Author contributions Conceptualization, data collection, data analysis and writing - original draft were performed by Yu Zhao. Material preparation and investigation were performed by Bingbing Li, Zhouxinnan Xu and Zhiheng Song. Project administration and funding acquisition were performed by Min Wang and Songyi Huang. Supervision and writing - review & editing were performed by Min Wang. All authors read and agreed to the published version of the manuscript. References Ansley, R. J. (2006). Soil organic carbon and black carbon storage and dynamics under different fire regimes in temperate mixed‐grass savanna. Global Biogeochemical Cycles, 20 (3), 3006. doi:https://doi.org/10.1029/2006GB002698Bird, M. I. (1999). 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Availability of data and material Data sharing not applicable to this article as no datasets were generated or analysed during the current study Code availability The custom code and/or software application generated during and/or analysed during the current study are available from the corresponding author on reasonable request. Ethics approval Not applicable. Consent to participate Not applicable. Consent for publication All authors gave their informed consent to this publication and its content. Supplementary Material File (figure.pdf) Download 2.03 MB Information & Authors Information Version history V1 Version 1 13 August 2025 Peer review timeline Published Land Degradation & Development Version of Record 10 Dec 2025 Published Copyright This work is licensed under a Non Exclusive No Reuse License. Collection Land Degradation & Development Keywords black carbon meta-analysis urban soil urbanization carbon neutrality Authors Affiliations Yu Zhao Zhongkai University of Agriculture and Engineering View all articles by this author Bingbing Li Zhongkai University of Agriculture and Engineering View all articles by this author Zhouxinnan XU Zhongkai University of Agriculture and Engineering View all articles by this author Zhiheng Song Zhongkai University of Agriculture and Engineering View all articles by this author Songyi Huang Zhongkai University of Agriculture and Engineering View all articles by this author Min Wang 0000-0002-6896-2375 [email protected] Zhongkai University of Agriculture and Engineering View all articles by this author Metrics & Citations Metrics Article Usage 276 views 138 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Yu Zhao, Bingbing Li, Zhouxinnan XU, et al. 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