Quantification of microbial community contributions to phosphorus speciation transformation in plateau lake sediments: Evidence from phosphate oxygen isotope fractionation and 16S rRNA gene sequencing

Understanding multiform phosphorus (P) biogeochemical cycling processes is crucial for mitigating eutrophication in aquatic environments. However, research on quantifying the contributions of different microbial genera to P migration and transformation is insufficient. This study aimed to investigate microbe-mediated P cycling processes in the sediments of a typical eutrophic lake, Dianchi, China, using 16S rRNA gene sequencing and phosphate oxygen isotope techniques. The results showed that phyla Proteobacteria, Acidobacteria, Firmicutes, and Chloroflexi were the key microbial communities influencing P cycling processes in the sediments. Phosphate oxygen isotope analysis revealed the potential proportions of external P inputs, with livestock farming (46.3 %) and P mining (30.1 %) identified as the largest contributors. Random forest analysis, used to characterize microbe-mediated fractionation processes of different P forms, revealed that microorganisms most strongly influenced H₂O-P and NaHCO₃-P, followed by NaOH-P. In contrast, their impact on the more stable HCl-P was minimal. Structural equation modeling was used to quantitatively determine the weight order of key microbial taxa as Actinobacteria > Proteobacteria > Acidobacteria > Ignavibacteriae. Notably, environmental factors (chemical oxygen demand, total nitrogen, and dissolved oxygen) may modulate microbial community composition and metabolism, thereby indirectly regulating P cycling. A significant correlation between most environmental factors and NaHCO₃-P was observed. For example, total nitrogen contributed 14 % in NaHCO₃-P compared with 1 % in NaOH-P. This study highlights the complex interactions between microbial communities and P cycling in natural environments, providing novel insights into the microbial mechanisms of P cycling and offering a theoretical basis for managing ecological restoration in eutrophic lakes.