Legume-maize rotation and nitrogen fertilization boost microbial communities to enhance soil function and maize yield

Sweet maize is a high-value crop in North China, yet how legume-maize rotation interacts with nitrogen (N) fertilization to regulate productivity, soil quality (SQI), ecosystem multifunctionality (EMF), and microbial communities remains unclear. To address this gap, we conducted a two-year field experiment comparing legume-maize rotation (SM) with double maize (DM) under three N fertilization rates (0N, LN, and HN). We quantified maize yield, SQI, EMF, microbial diversity, co-occurrence networks, and integrated pathways linking management practices with soil functions and yield. Maize yield in SM was 12.2%-26.6% higher (P < 0.05) than that in DM under 0N and LN, whereas no significant difference was observed under HN across the two experimental years. Compared with DM, SM increased EMF by 4.5%-29.9% and SQI by 4.2%-18.2% (P < 0.05). SM also promoted bacterial and fungal diversity, with Shannon and Chao1 indexes being 3.6%-9.5% and 4.2%-18.2% higher, respectively (P < 0.05). Co-occurrence network analysis indicated that SM exhibited greater microbial connectivity and a higher proportion of positive associations under 0N and LN than DM. Correlation analyses linked key bacterial taxa (Nitrospirota and Chloroflexi) and fungal taxa (Mortierellomycota) with SQI and EMF. Subsequently, structural equation modeling suggested that N fertilization exerted a direct effect on maize yield, whereas SM increased maize yield indirectly by elevating SQI and EMF through shifts in microbial community composition and interactions. These findings suggest that legume-maize rotation with suitable N input benefits sweet maize productivity, soil quality, and multifunctionality, providing a sustainable intensification pathway for sweet maize-based cropping systems.