Evidence synthesis of soil carbon dynamics: A multi-scale meta-analysis integrating land-use change, conservation practices, and environmental stressors

Systematic evidence synthesis in soil science is crucial for developing effective climate mitigation strategies and sustainable land management practices. This study presents an integrated meta-analytical framework synthesizing three interconnected domains of soil carbon dynamics: land-use transitions, conservation management, and emerging environmental stressors. Through quantitative analysis of peer-reviewed studies, we evaluated the multifaceted responses of soil organic carbon (SOC) and associated biogeochemical processes to management interventions and environmental changes. Land-use conversion analysis suggested that grassland restoration from croplands significantly enhances SOC (16%) and total nitrogen (12%), while inducing substantial shifts in microbial stoichiometry (C:P ratio +57.9%). Conservation management practices, particularly no-tillage with residue retention, increased SOC stocks (13%) relative to conventional tillage, accompanied by enhanced microbial biomass carbon (33%) and nitrogen (64%). The implementation of grass coverage in orchards further augments these benefits, increasing microbial abundance (52.6%) and diversifying enzyme activities (15-71%). Environmental factors, including mean annual temperature, precipitation, and soil texture, emerged as critical drivers of these responses across all management interventions. Analysis of emerging stressors found that drying-rewetting cycles significantly increased soil carbon dioxide emissions (35.7%), while microplastic contamination enhanced nitrogen-cycling enzyme activities (7.6-8.0%) and SOC dynamics in polymer-specific patterns. Meta-regression analyses identified key thresholds and optimal conditions for maximizing soil carbon sequestration potential across different environmental contexts. This comprehensive evidence synthesis indicates the interconnected nature of soil carbon responses to management and environmental change, while establishing quantitative parameters for context-specific interventions. The findings provide support for policy frameworks promoting integrated approaches to soil conservation and climate-smart management strategies, particularly in vulnerable agricultural systems facing multiple environmental stressors.