Effects of N and P Fertilization on Soil N-Cycling Microbial Community Structure in White Clover Grasslands

Although nitrifying and N-fixing functional gene microbes play a crucial role in regulating ecosystem nitrogen (N) cycling, understanding of how N and phosphorus (P) fertilization affect their community structure remains limited. N fertilizer levels were set to simulate N deposition and combined with different P fertilizer levels, to explore the soil-root-shoot physiological indexes, and the response of community structure of N-fixing and nitrifying microorganisms that caused changes in the N cycle of the system to fertilization. The results showed that N and P fertilization significantly decreased soil N pool (NH₄⁺-N, NO₃^--N, IN), the concentrations of shoot TN, root TP, root OC, and root biomass, and slowed down soil N flux (net ammoniation rate, net nitrification rate, and net N mineralization rate). This effect was more pronounced under NP fertilization compared to single N or P fertilization. Short-term N and P fertilization had little effect on AOA and AOB. Anaeromyxobacter is a dominant genus of diazotrophs, and its relative abundance was significantly improved by N fertilization. Fertilization significantly increased Geobacter, but significantly decreased the relative abundance of Zoogloea, Rhizobium, and Azohydromonas. Root biomass and TP, soil NH₄⁺-N, OC, and AP changed by fertilization were the main factors affecting N-fixing microorganisms. This study showed that in addition to soil N, soil OC and P changes caused by fertilization were also important factors affecting the N-cycling microbial community structure. Later relevant studies should also consider the effect of fertilization duration, environmental temperature, soil base condition, etc.