Litter chemical traits, microbial and soil stoichiometry regulate organic carbon accrual of particulate and mineral-associated organic matter

Plant litter quality considerably affects C accrual in soil organic matter (SOM). However, the chemical traits of litter that influence C distribution in SOM fractions, such as particulate organic matter (POM) and mineral-associated organic matter (MAOM), are not fully understood. Thus, we conducted a 150-day incubation experiment with litter addition (poplar leaves, roots, grasses grown under the canopy, and a mixture of these three litter types). We analyzed the organic C concentration in the POM and MAOM fractions and the stoichiometric ratios (C:N:P) of the soil and microbial biomass 50, 100, and 150 days after the initial litter addition. Microbial residue C (amino sugar biomarkers) in SOM fractions was registered at the end of decomposition. High-quality litter (i.e., leaf) increased MAOM-C accrual, and low-quality litter (i.e., root and grass) contributed more to POM-C accrual. The mixed litter addition accumulated more C in the SOM via high POM-C levels compared to single litter input, likely resulting from an antagonistic effect caused by different litter trait dissimilarity. Moreover, POM-C dynamics were dominated by litter chemical traits during litter decomposition, and MAOM-C was controlled mainly by microbial and soil stoichiometry. Furthermore, the contribution of microbial residue C to SOM (especially POM-C) was lower in the mixed litter than in the single litter. These findings highlight the direct or indirect impacts of litter types on the C dynamics of POM and MAOM, and demonstrate that litter diversity is conducive to C accumulation in SOM.