Nitrogen Addition Increases the Organic Residue‐Induced Carbon Mineralization by Shifting Soil Bacterial and the Fungal Community Structure and Co‐Occurrence Network

ABSTRACT Organic residue plus nitrogen (N) fertiliser is an efficient method for improving agricultural soil quality and yield. However, it also induces organic carbon (C) loss through mineralization. Soil microorganisms are involved in regulating the soil C cycle; however, the microbial community and keystone taxa to regulate organic C mineralization and their underlying factors in orchard remain unclear. To address this, soil samples from apple orchard were collected and amended with wheat straw combined with different levels of N (0 mg kg −1 , S; 200 mg kg −1 , S + RN; 300 mg kg −1 , S + CN; 500 mg kg −1 , S + HN), soil without any straw or N as CK, and incubated for 110 days in a laboratory. Wheat straw increased the CO 2 efflux rate, especially the N supply, in the following order: S + HN > S + CN > S + RN > S > CK. The cumulative mineralization of organic C (C min ) under straw addition and straw plus N input were higher than that under CK. At the end of incubation, the straw plus N treatments increased C min by 15.02% (S + RN), 20.06% (S + CN), and 32.45% (S + HN) compared with treatment S. Straw plus N increased the relative abundance of Actinobacteria and Chloroflexi but decreased that of Acidobacteria, Myxococcota, and Latescibacterota. The co‐occurrence network indicated that the additional N supply led to simpler and less complex microbial networks in soil under wheat straw. The keystone taxa of bacteria, Acidobacteria and Latescibacterota, were negatively correlated with C min . Meanwhile, Entotheonellaeota and Actinobacteria of the bacterial phylum and Basidiomycota of the fungal phyla were positively correlated with C min . Straw plus N application increased the positive/negative links of fungi. This indicates that the alleviated competitive interactions coupled with keystone taxa in the fungal network dominated the promotion of C min . Structural equation model analysis showed that soil bacterial communities and fungal networks were key factors that increased soil enzyme activities and induced organic C mineralization. Wheat straw combined with N fertiliser reduction may be a sustainable strategy for mitigating organic C mineralization in orchard soils.