High Nitrogen Fertilizer Input Enhanced the Microbial Network Complexity in the Paddy Soil

Abstract

Nitrogen (N) fertilization drives the composition and function of soil microbial communities, which are crucial for regulating soil biogeochemical cycling and maintaining ecosystem stability. The influences of N fertilizer on soil microbial composition and diversity have been widely explored, while it is commonly overlooked that ecosystem processes are carried out via complex webs of co-occurrence networks among microbiome members. Here, we examined the effects of five N fertilization levels (0, 135, 180, 225, and 360 kg N ha-1) on microbial co-occurrence networks and key functional taxa such as ammonia-oxidizers in paddy soils. The results showed that N addition altered microbial community composition, which were positively related to soil total N and available phosphorus (P) contents. The abundance of ammonia-oxidizing archaea (AOA) significantly decreased after N addition, whereas ammonia-oxidizing bacteria (AOB) increased in N360 treatment. Compared with low-N group (N0 and N135), the high-N group (N225 and N360) shaped more complex microbial webs and thus improved the stability of the microbial community. Partial least squares path modelling further revealed that N fertilizer had a higher effect on microbial network complexity in the high-N group (0.83) than the low-N group (0.49). Although there were more positive links across all microbial networks, the proportion of negative links significantly increased in the high-N networks, suggesting that excess N addition aggravated the competition among microbial species. Disentangling these interactions between microbial communities and N fertilization advances our understanding of biogeochemical processes in paddy soils and their effects on nutrient supply to rice production. Our findings highlighted that highly N-enriched paddy soils have more stable microbial networks and can better sustain soil ecological functions to cope with the ongoing environmental changes.

Keywords: Paddy soil, Nitrogen fertilizer, Co-occurrence network, Microbial interaction