Keystone bacterial functional module activates P-mineralizing genes to enhance enzymatic hydrolysis of organic P in a subtropical forest soil with 5-year N addition

Abstract

Microorganisms play an integral role in driving phosphorus (P) transformation in forest soils; however, studies on soil P cycling and the molecular mechanisms of microbes activated in response to elevated nitrogen (N) deposition are limited. In this study, we conducted a multilevel field N enrichment experiment in a subtropical P-deficient Moso bamboo (Phyllostachys heterocycla) system to evaluate the microbial ecological traits of P transformation (e.g., organic P mineralization and inorganic P solubilization) over three consecutive years. N addition significantly decreased available and organic P levels in the soil and increased the microbial biomass C:P and N:P ratios, indicative of severe microbial P limitation. Consequently, N addition increased the absolute abundance of P starvation response regulation genes (phoU and phoR), which further induced an increase in organic P mineralization (phoN, phoD, appA), but not that of inorganic P solubilization genes (ppx and gcd). This suggests that microbes enhance P availability by organic P mineralization rather than inorganic P solubilization to ameliorate reduced P availability. Furthermore, a bacterial functional module (B_Mod#0) consisting of Proteobacteria, Actinobacteria, and Firmicutes accounted for more than 60% of the changes in the abundance of genes responsible for organic P-mineralization in the soil, suggesting that B_Mod#0 acts as a keystone phylotype in enhancing functional P-cycling potential. This study provides novel insights into microorganism-driven P cycling in P-deficient forest soils with N addition.