Using 13C15N Labeling Technology to Reveal the Fate of Maize Straw in Soil Organic Matter and Dissolved Organic Matter under Different Exogenous Microorganism-Mediated Conditions

Understanding the fate of maize straw in soil organic matter (SOM) and dissolved organic matter (DOM) is essential for identifying key processes in plant residue (PRe) decomposition. This study quantified the distribution of maize straw-derived carbon (C) and nitrogen (N) in SOM and DOM under different exogenous microorganisms using 13 C 15 N labeling. Treatments included fungi ( Trichoderma reesei, Trichoderma harzianum, and Phanerochaete chrysosporium ), bacteria ( Bacillus subtilis ), and combinations. Fungal addition increased the straw-derived C by 2.79%–6.97% after 360 days, with no significant effect on N compared with bacteria. Microbial combinations achieved the highest PRe conversion but depleted SOM without increasing total C or N. Trichoderma enhanced early dissolved organic C (DOC) and N (DTN) release; Trichoderma reesei showed the highest DOC retention (15.85%) at 360 days. All microbial treatments increased soil DTN, with fungi showing the greatest effect. Trichoderma reesei best facilitated PRe transformation and minimized the SOM loss. Overall, fungal and combined microbial treatments more effectively promoted PRe-derived DOM formation.