Nitrogen mineralization as a result of phosphorus supplementation in long-term phosphate deficient soil

• P supplement triggered N mineralization in P deficient soil.
• AOB was sensitive to P application in red soil.
• 50 mg kg−1 of P is a threshold for N nitrification.

In red soil (with pH ≤6), high phosphorus deficiency hinders soil carbon and nitrogen cycling, and thus reduces plant nutrient use efficiency in terrestrial system. In this study, inorganic phosphate addition could accelerate litter nitrogen release and soil nitrogen mineralization through stimulating soil urease and dehydrogenase enzymatic activities. The abundance and composition of mineral N transforming genes with three levels of phosphate were assayed using quantitative real-time PCR and denaturing gradient gel electrophoresis. Soil ammonia-oxidizing bacteria (AOB) were sensitive to the inorganic phosphate supplementation level: P addition at levels lower than 25 mg kg−1 accelerated soil nitrification via increased AOB activity. However, as the P level reached 50 mg kg−1, higher levels of soil ammonium nitrogen from litter decomposition remained in the soil through a decrease in the activities of N-mineralization enzymes and the stabilization of the AOB community structure. Our results emphasize the importance of reasonable concentrations of P fertilization for accelerating litter N mineralization and avoiding N leaching in plant litter-amended soil where phosphate is deficient.