Background and aimsPhosphorus (P) fertilizer is essential for improving crop yield, especially in arid agricultural regions. While P application is known to influence rhizosphere microbial communities, the effects of excessive P application on microbial diversity and functionality-particularly those microbes involved in plant growth-remain poorly understood.MethodsWe conducted a field experiment with four P addition levels (0, 44, 87, and 131 kg P ha(-)1 yr(-)1) in the arid region of China. The effects of P fertilization on soil bacterial communities, rhizosphere microbial functions, co-occurrence patterns, and cotton growth were examined.ResultsThe highest seed cotton yield (5224 kg ha(-)1) and rhizosphere microbial diversity occurred at 87 kg P ha(-)1 yr(-)1. This level significantly increased both microbial taxonomic and functional diversity, while a decline in diversity was observed at the 131 kg P ha-1 yr(-)1, suggesting a threshold effect. Network analysis of microbial ecological associations corroborated these patterns. Notably, rhizosphere microbial functional diversity, rather than taxonomic diversity, exhibited a significant correlation with cotton yield. Multivariate correlation analysis and structural equation modeling established that P addition directly affected soil properties and indirectly caused shifts in the abundance of beneficial microbial taxa linked with improved root growth and yield. Although 87 kg P ha(-)1 yr(-)1 represented moderate input that balanced rhizosphere function and plant growth, it still exceeded cotton's removal.ConclusionsThis study underscores the intricate interplay between P application, rhizosphere microbial ecology, and plant growth, revealing that excessive P input disrupted these patterns without further yield benefits.