Nitrogen addition and rhizosphere effects differentially shape prokaryotic and fungal communities in peanut–maize cropping systems

Abstract

The role of nitrogen (N) fertilization in enhancing crop yields and mixed cropping in reducing continuous cropping obstacles have been well documented. However, N fertilization and mixed cropping on rhizosphere and bulk soil microbial diversity, community structure, and plant growth remain controversial. To address this knowledge gap, we conducted a pot experiment of two plant species (peanut (Arachis hypogaea L.) and maize (Zea mays L.)), three N addition levels (0, 150, and 225 kg N hm⁻²), and two cropping systems (monoculture and mixed cropping). To investigate rhizosphere and bulk soil prokaryotic and fungal community response to N addition in different cropping systems, high-throughput sequencing technology was used in this study. Overall, under the mixed cropping condition, compared with N₀ addition level, N₂ addition level increased maize aboveground biomass (AGB) by 205.62 % and maize belowground biomass (BGB) by 45.36 %, but reduced peanut AGB by 12.60 % and peanut BGB by 24.07 %. Moreover, with increased N fertilization, the BGB/AGB ratio of peanut under mixed cropping decreased first from 0.22 to 0.18, and then increased up to 0.23. The α-diversity of soil prokaryotic community decreased significantly with increasing N addition levels, while the observed ASVs of the rhizosphere fungal community was significantly lower than that of bulk soils. The results of non-metric multidimensional scaling (NMDS) combined with PERMANOVA analysis showed that the clustering of soil microbial communities was mainly dominated by the rhizosphere and N effects. In addition, Mantel test results showed that the changes of the rhizosphere environmental factors drove the changes in fungal community composition, while the changes of bulk soil environmental factors drove the changes in prokaryotic community composition. Microbial network co-occurrence analysis indicated that N addition increased the complexity of the soil prokaryotic network structure, but reduced the complexity of the soil fungal network structure. Meanwhile, the network structure complexity of prokaryotic and fungal communities in the rhizosphere were higher than that in bulk soils. The above results comprehensively suggested that N addition mainly changed soil prokaryotic community composition, while rhizosphere effects primarily altered soil fungal community composition. This may be caused by the survival strategy of soil microbes (r/K strategists) and the background environmental differences between the rhizosphere and bulk soils.