Short-term nitrogen addition improves soil phosphorus availability by regulating phosphorus-cycling microbial communities in a karst forest

• N addition improved soil P availability in karst soils. • N addition promoted microbial transformation from organic P to available P. • N addition increased the abundance and richness of P-cycling microbes. • N-induced P-cycling microbial genes differed between bulk and rhizosphere soils. The widening imbalance between escalating nitrogen (N) deposition and depleting soil phosphorus (P) amplifies the urgency of investigating P cycling processes in terrestrial ecosystems. However, the mechanisms by which P-cycling functional profiles drive soil P mobilization under enhanced N deposition remain to be addressed. After a three-year N-addition experiment at varying rates in a karst forest, we determined the soil P fractions and associated bacterial communities involved in regulating P cycling in rhizosphere and bulk soils. Our results showed that N addition increased plant-available P in both bulk soil (+17 % under low N, +22 % under high N) and rhizosphere soil (+6%, +23 %), while concurrently reducing organic P in bulk soil (−18 %, −24 %) and rhizosphere soil (−8%, –23 %) under corresponding N rates. In addition, N treatment substantially shifted the composition of the P-cycling bacterial community and increased the richness of the community, indicating that N input enhances P availability, potentially through the regulation of the bacterial communities involved in P cycling. Moreover, we found that the functional bacterial genes responsible for P transformation differed between the bulk and rhizosphere soils. Specifically, in the bulk soil, P mineralization genes and P solubilization genes were significantly increased by N treatment. In contrast, in the rhizosphere soil, P mineralization and P regulation genes increased in response to N addition. Together, these results suggest that N addition improves soil P availability by regulating P-cycling functional bacterial communities; however, the specific functional profiles driving P mobilization may differ between bulk and rhizosphere soils. These findings provide novel insight into the regulatory processes of soil P cycling in terrestrial ecosystems under global changes (e.g., N deposition) from a microbial gene perspective.