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 dynamics in soil Fe-OC and ROS following mulching in banana orchards remain unclear. This study investigated the impact of 3 years of straw mulching on soil Fe-OC, ROS, and soil C mineralization. The results showed that Fe-OC content decreased significantly in the first year of straw mulching, attributed to a weakened Fenton reaction, reduced reactive Fe oxides, and increased soil pH. In the subsequent two years, increased dissolved organic carbon (DOC) mitigated the negative impact on Fe-OC, preventing further significant reductions. Meanwhile, straw mulching significantly lowered soil ROS (O₂^·− and ·OH) levels over the three years, contrary to the hypothesis that it would increase ROS by promoting microbial biomass. This reduction was linked to increased soil pH and a weakened Fenton reaction. Moreover, straw mulching significantly increased soil C mineralization in the second and third years but had no significant effect in the first year. Despite the potential negative impact of reduced ROS, straw mulching promoted soil C mineralization by increasing soil microbial activity and C sources. The distinct responses of soil C mineralization to straw mulching in the first year compared to the following two years suggest that the overall impact of straw mulching on this process is determined by the trade-off between the Fenton reaction and microbial activity. These results indicate that straw mulching significantly influenced soil Fe-OC, ROS, and C mineralization by modulating the Fenton reaction, microbial activity, and soil physicochemical properties, with specific changes varying depending on the duration of mulching. These insights enhance our understanding of how straw mulching drives soil C cycling in agricultural ecosystems.