Effects of land reclamation on soil organic carbon and its components in reclaimed coal mining subsidence areas.

The accumulation of soil organic carbon (SOC) is crucial for the development and ecosystem function restoration of reclaimed mine soils (RMSs). To optimize reclamation management practices, this study aims to explore the factors and underlying mechanisms influencing the recovery of SOC and its components in RMSs from a systemic perspective using complex network theory (CNT). This study focused on coal mining subsidence areas in the eastern mining regions of China, comparing reclaimed cultivated land with surrounding non-subsided cultivated land. Soil samples were collected at depths of 0-20 cm, 20-40 cm, and 40-60 cm, and 25 soil indicators were measured. CNT was applied to explore the intricate relationships between soil indicators and to identify the key factors and underlying mechanisms influencing SOC and its components in RMSs. The results revealed that the compaction-induced soil structural damage during the reclamation process led to a chain reaction, resulting in increased soil bulk density (11.92 % to 15.03 %), finer soil particles (5.00 % to 9.88 % more clay and silt), and enhanced SOC mineralization (SOC decreased by 10.70 % to 15.62 % with a lower C/N ratio by 2.30 % to 28.55 %). Microbial activity also decreased, with a 6.25 % to 13.16 % drop in MBC and a 0.91 % to 27.68 % decrease in enzyme activity. The utilization of active SOC fractions by more adaptable bacterial communities was crucial within this chain reaction process. The intermediate role of soil structure in the RMS ecosystem, particularly in carbon cycling, becomes more prominent. RMSs exhibited heightened sensitivity to soil structure changes, with the response of microorganisms and enzymes to soil structure changes being pivotal. In the carbon cycling process of RMSs, microbial-driven enzyme activity in response to soil structure was more critical during SOC transformation, while the role of physical-chemical protection and microbial inhibition mediated by iron‑aluminum oxides became more pronounced in stabilizing SOC.