Temporal dynamics of nutrient release from mulching of legume roots and shoots litter driven by microbial community during decomposition in organic orchards

Grass residue decomposition is crucial for nutrient cycling in agro-ecosystems, enhancing nutrient utilization efficiency and supporting sustainable crop management. While grass mulching has been widely studied for improving orchard soil fertility, the role of soil microbial communities in decomposing different plant organs remains unclear. Before decomposition, the aboveground and belowground plant parts were harvested and placed in separate litterbags, which were later used for evaluating the decomposition rate and chemical characteristics of the shoots and roots for 40 days (at 10 days intervals). The changes in soil fertility, soil microenvironment, soil microbial community were measured after 0, 1 and 3 months, alongside analysis of key microbial taxa under different residues treatments. The remaining mass of root litter treatment was significantly higher than that of other treatments by 72.97%, 17.53% during 1-10 days and 30-40 days, respectively. During the 40-days period, the release of potassium (K) from root litter reached 58.61%, and the decomposition of lignin was recorded at 56.94%, whereas the release of carbon (C), nitrogen (N), and phosphorus (P) remained relatively stable. Despite no significant changes in nodes, edges, and links at 30 and 90 days, the co-occurrence network of root litter exhibited modularity values of 0.774 and 0.773, respectively. The values were higher than those observed in random networks, indicating the presence of functional modules and enhanced stability within the root microbial community. Litter organs enhanced decomposition rates by positively influencing soil fertility and keystone microbial decomposers, while its soil microenvironment affects decomposition rates. Despite its recalcitrance, the chemical composition of root litter plays a key role in regulating soil microbial community structure and improving soil fertility, thereby maintaining orchard ecosystem functionality.