Interactive effects of soil erosion and mechanical compaction on soil DOC dynamics and CO₂ emissions in sloping arable land

Soil erosion and mechanical compaction on sloping arable land can significantly influence soil carbon turnover. However, the interactive effects of soil erosion and mechanical compaction on soil carbon dioxide (CO2) emissions, temperature sensitivity (Q(10)), and dissolved organic carbon (DOC) in sloping arable soils remain uncertain. This study aimed to explore the effects of three mechanical compaction levels: heavy compaction (HP), light compaction (LP), and no compaction (NP), on DOC characteristics, CO2 emissions, and Q(10) in both erosional and depositional sites. Two locally widely used tractors, a 220 horsepower (high pressure, HP) and a 25 horsepower (low pressure, LP), were used to simulate different levels of soil compaction by traveling back and forth through the ridge and furrow three times. We found that the DOC concentration in the depositional site was 15.8 % higher than that in the erosional site without compaction; however, after HP, the DOC concentration in the depositional site was 82.6 % higher than that in the erosional site. HP reduced DOC concentration in the erosional site by 26.1 %, while DOC concentration in the depositional site increased by 16.5 %. LP reduced DOC concentration in the erosional site but did not result in significant changes in the depositional site. Notably, the effect of HP on C mineralization varied with erosional and depositional sites. In the erosional site, HP increased CO2 emissions by 29.4 % and 36.7 % at 15 degrees C and 25 degrees C, respectively, compared with NP. Conversely, in the depositional site, HP decreased CO2 emissions by 27.8 % and 31.3 % compared with NP at the same temperatures, respectively. LP did not have a significant effect on CO2 emissions at the erosional and depositional sites. Furthermore, soil CO2 emissions from sloping arable land were primarily regulated by soil DOC content and DOC properties such as hydrophobicity and molecular weight. Intensive mechanical compaction significantly altered the concentration and quality of DOC in sloping land, thereby leading to notable changes in CO2 emissions and a heightened Q(10) response. These findings emphasize the intricate nature of soil compaction and erosion interactions, and their potential implications for the carbon cycle in terrestrial ecosystems.