Compaction shapes CO2 emission contrasts in sloping farmland: Erosion-deposition zones respond via soil structure and microbiome

Abstract

Mechanical compaction and water-induced soil erosion are critical factors influencing soil carbon cycling, particularly on sloped agricultural land. However, their combined effects on soil physicochemical properties, microbial community composition, and CO₂ emissions remain insufficiently understood. This study examined the interactive effects of three levels of mechanical compaction—no pressure (NP), low pressure (LP), and high pressure (HP)—at both depositional and erosional sites. The results revealed that compaction and erosion significantly altered soil structure, microbial communities (assessed using the PLFA method), and CO₂ influxes. HP reduced soil porosity and aggregate stability, intensifying soil degradation at erosional sites while leading to organic carbon accumulation at depositional sites. Changes in microbial communities were evident, with shift in bacterial-to-fungal ratios depending on site conditions. Increased CO₂ emissions at erosional sites were associated with soil structure collapse, whereas enhanced specific surface area at depositional sites contributed to lower emissions. Given that erosional areas generally exceed depositional ones on slopes, compaction-induced erosion led to an overall increase in CO₂ emissions, as emissions increased in eroded areas but decreased in depositional zones. This study elucidates the mechanisms by which compaction erosion zones and depositional zones induce different CO₂ emissions. In conclusion, the findings highlight the critical role of compaction and erosion in driving carbon cycling on sloped agricultural land. To mitigate CO₂ emissions and enhance soil carbon storage, targeted management strategies should focus on reducing soil compaction and preventing erosion, especially in areas prone to degradation.