Soil C mineralization and C-Fe coupling: a trade-off between Fenton reaction and microbial activity under straw mulching in banana orchards

Straw mulching influences soil carbon (C) cycling by adding organic matter and modifying the soil structure, with soil iron (Fe)-associated C (Fe-OC) and reactive oxygen species (ROS) playing critical roles in this process. However, the changes in soil Fe-OC and ROS following mulching in banana orchards remain unclear. This study established experimental fields with 3 years of continuous straw mulching to examine its effects on soil Fe-OC, ROS, and soil C mineralization. Straw mulching weakened the Fenton reaction by increasing the soil pH, soil organic C, and soil water content, thereby decreasing the ROS content. The reduced Fe-OC was attributed to the weakening of the Fenton reaction, the decreased reactive Fe oxides, and the elevated soil pH. Although straw mulching negatively impacted soil C mineralization via reducing ROS, it also promoted soil C mineralization through enhancing microbial activity and decreasing Fe-OC, resulting in significantly increased soil C mineralization. The multi-batch straw mulching pattern in banana orchards resulted in different dynamics in Fe-OC and soil C mineralization in the first year after mulching compared to the subsequent two years. This mechanism, by which straw mulching promotes soil C mineralization through weakening the Fenton reaction, decreasing Fe-OC, and increasing microbial activity, contributes to a deeper understanding of C cycling in agricultural ecosystems under straw mulching.