Responses of carbon and microbial community structure to soil nitrogen status vary between maize and potato residue decomposition

Plant residue decomposition is a core process in the soil carbon (C) cycle. Soil nitrogen (N) status regulates organic C chemical structure during crop residue decomposition and subsequent C sequestration significantly. Therefore, understanding how soil N status influences changes in organic C chemical structure during residue decomposition is crucial for effective C management in croplands. In this study, maize (M) and potatomonoculture (P) soils with two N statuses (N0, unfertilized; and N2, 250 and 125 kg N ha-1 for M and P, respectively) were used as decomposition environments to conduct 6-month decomposition of maize and potato residue. According to the results, soil N status had no significant effect on mass loss but changed the organic C chemical structure for both residues. Alkyl C and aliphaticity increased in maize residue but decreased in potato residue under N2 relative to under N0. High N availability increased bacterial-fungi interactions, abundance of cellulose and chitin degradation genes (exoglucanase and chitinase), and enzyme activity (chitinase and sucrase) in maize residue. However, the response of potato residue to N status was opposite to that of maize residue. The structural equation model indicated that the increase in soil NO3 � -N reduced residue C/N, changed microbial community structure and keystone species in residues, and increased enzyme activities, in turn altering recalcitrant C contents in the decomposed residues. Our results highlight the differential impact of soil N status on organic C chemical structure in different residues, and the coupling relationship between microbial communities and organic C structure during residue decomposition in farmland soil.