Effect of Phosphorus Addition on Rhizosphere Soil Microbial Diversity and Function Varies with Tree Species in a Subtropical Evergreen Forest

Despite the fact that rhizosphere soil microorganisms play a critical role in nutrient cycling, the effects of phosphorus (P) addition on microbial diversity in subtropical evergreen forests remain insufficiently understood. In this study, we examined how P fertilization influences rhizosphere microbial communities and enzyme activities in two dominant tree species, Schima superba and Castanopsis fargesii, using colorimetric analyses and high-throughput sequencing. The results showed that P addition significantly increased microbial diversity in the rhizosphere of S. superba but not C. fargesii. This response in S. superba was associated with shifts in saprotrophic microorganisms. Although P addition increased the abundance of Acidobacteria and Zygomycota in both species, the mechanisms underlying the microbial responses differed, reflecting the contrasting nutrient acquisition strategies of their mycorrhizal types. Soil-available P primarily shaped bacterial community composition in S. superba, whereas total nitrogen and soil pH were key drivers in C. fargesii. P fertilization also altered several C- and N-cycling enzyme activities, which were driven by differential regulation of the soil microbial community in two species. Overall, our findings demonstrate that the effects of P addition on rhizosphere microbial diversity and function vary substantially between tree species, highlighting the importance of plant–microbe interactions in regulating nutrient cycling in subtropical forests.