Straw mulching decreased the contribution of Fe-bound organic carbon to soil organic carbon in a banana orchard

The association between iron (Fe) oxides (Fe-O) and organic carbon is a vital mechanism for the long-term accumulation and stabilization of soil organic carbon (SOC). To thoroughly explore the impacts of straw mulching on Fe-bound organic carbon (Fe-OC), we conducted a mulching application experiment in a 2-year no-tillage banana orchard. Two treatments (a 2-year straw mulching treatment and no straw return treatment) were established using a randomized complete block design. The Fe-OC and SOC pools in the surface soil were determined, and the results showed that straw mulching significantly increased the SOC contents by 34.02 %, and soil Fe-OC accounted for approximately 12.24 %–25.34 % of the SOC. Compared with the control treatment, straw mulching significantly decreased the Fe-OC contents and their contribution to SOC, which may have been due to soil dithionite-extractable Fe oxide (Fed) contents, the abundance of the Acidibacter, and α-glucosidase activities. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy indicated that straw mulching increased the colocalization between cellulose/hemicelluloses and peptides, and the relationships among lignin, Fe-O, and peptides became stronger than those in the CK treatment. These findings imply that straw mulching may decrease Fe-OC pools through various physicochemical and microbial mechanisms, these soil Fe-OC contents may be preserved as lignin derivatives and microbial-derived organic compounds.