Effects of rainfall-induced physical crusts on soil carbon distribution and mineralization through surface pore structure

The vast carbon sequestration potential of soil implies that even minor changes in its characteristics can impact atmospheric carbon levels. However, little research has focused on the influence of rainfall-induced physical crusts, a common natural phenomenon, on soil organic carbon (SOC). In this study, we simulated contour farming patterns and induced artificial rainfall to obtain different types of physical crusts (structural and depositional crusts). We determined their effects on SOC mineralization rates and distribution and utilized XCT scanning technology to gather surface pore data, attempting to explain the reasons from the perspective of pore structure changes. The formation of physical crusts significantly enhanced SOC mineralization. During the 27-day mineralization experiment, the production of structural and depositional crusts increased cumulative mineralization rates by at least 23.07 % and 18.57 %, respectively. The underlying cause of this phenomenon is closely related to the drastic changes in soil pore structure, particularly the increase in the proportion of micropores and the enhancement of pore connectivity after crust cracking. Additionally, rainfall resulted in SOC enrichment in the surface crust but led to increased participation of subsoil organic carbon in the mineralization process. Consequently, the level of SOC in subsoil significantly decreased after the formation of physical crusts compared to soil without crusts. This study reveals the impact of rainfall-induced soil physical crusts on SOC release and storage and provides a microscopic pore perspective to explain the underlying mechanisms. Against the backdrop of global climate change, this research supplements theoretical understanding of the effects of rainfall events on soil carbon pools and predictions of soil organic carbon release.