Nitrogen availability of mung bean in plant-soil system and soil microbial community structure affected by intercropping and nitrogen fertilizer

Abstract

Cereal/legume intercropping can effectively boost farmland productivity and ecosystem functions through aboveground and belowground interaction. However, the impacts of intercropping on the growth performance of inferior crops and soil microbial community structure remain unclear, especially combined with different nitrogen (N) fertilizer input. This study investigated two cropping layouts: sole mung bean (SM), proso millet/mung bean intercropping (IM), each subjected to four N levels: 0 kg N ha⁻¹ (N0), 45 kg N ha⁻¹ (N1), 90 kg N ha⁻¹ (N2), and 135 kg N ha⁻¹ (N3). The results showed that compared with SM, IM significantly decreased the dry matter accumulation and N uptake of mung bean, resulting in lower N use efficiency and grain yield. Suitable application of N fertilizer was conducive to promoting the growth of intercropped mung bean, however, it still cannot reach the state of monoculture. Intercropping and N fertilizer significantly increased total N content, microbial biomass N content, as well as N-related enzyme activities in rhizosphere soil of mung bean, but decreased ammonium N and nitrate N content. These changes affected the community structure and diversity of soil microorganisms. The effect of intercropping on microbial diversity was greater than that of N fertilizer, as showed by Chao1 index and Shannon index. Redundancy analysis revealed that plant N uptake and stem N content were key factors affecting bacterial and fungal community structure. Intercropping and N fertilizer altered the topological network properties of soil microbial communities; the ecological connectivity of bacterial taxa was tighter than that of fungi. Our findings underscore the importance of field agricultural practices in affecting N availability of mung bean in plant-soil system and shaping rhizosphere community, thereby impacting the productivity of intercropping system. These results would provide important understanding for optimizing N utilization and management in legume-based intercropping systems.