Linking soil phosphorus fractions to abiotic factors and the microbial community during subalpine secondary succession: Implications for soil phosphorus availability

Soil phosphorus (P) availability plays a critical role in sustaining ecosystem productivity during vegetation succession. However, our understanding of the factors driving soil P dynamics along this process, particularly in cold regions like the Tibetan Plateau, remains poorly limited. To address this, we sampled soils from four vegetation types along a secondary successional gradient (grassland → shrubland → secondary forests → primary forests) in the subalpine region of the Tibetan Plateau. Our aim was to investigate the drivers of soil P dynamics along the successional gradient. We assessed soil P dynamics by analyzing sequential soil P fractions using a modified Hedley fractionation procedure. Our results revealed significant increases in the concentrations of total inorganic P (Pi) (58.3%), Resin-Pi (93.5%), NaHCO3-Pi (63.1%), and HCl-Pi (81.7%) along the successional gradient. In contrast, we did not observe any significant changes in total P or residual P concentration along the successional gradient. Soil organic P (Po; dominated by c. HCl-Po) initially increased by 16.7% but then exhibited a subsequent decrease by 37.5% during secondary succession. The observed increase in Pi was found to be linked to the accrual in soil organic carbon during vegetation succession. Conversely, the decrease in soil Po concentration was associated with the decline in vegetation richness and fungal richness along the successional gradient. Additionally, we identified the increased relative abundance of Basidiomycota, Mortierella and Russula as potential contributors to the decrease in the soil Po concentration in the late, mid, and late successional stages, respectively. Overall, our study underscores the joint influence abiotic factors and the microbial community on soil P dynamics during vegetation succession. These findings provide valuable insights into the processes influencing soil nutrient availability in cold regions such as the Tibetan Plateau.