Abstract: Moso bamboo (Phyllostachys edulis) forests, an important forest resource in subtropical China, are facing phosphorus (P) limitation and nitrogen (N)-P imbalance caused by N deposition. Although biochar has the potential to improve soil quality, its role in addressing N-induced P limitation is still unclear. We investigated the main and interactive effects of N (0, 30, and 90 kg N·hm^-2·a^-1) and biochar (0, 20, and 40 t·hm^-2) addition on P fractions (CaCl₂-P, Citrate-P, Enzyme-P, and HCl-P) in the rhizosphere soil of Moso bamboo forests. The results showed that the addition of N or biochar alone significantly increased Citrate-P, available phosphorus, contents and microbial biomass phosphorus  in rhizosphere soil, but significantly decreased soil pH (P<0.05). Under the conditions of N addition, biochar addition significantly increased rhizosphere soil CaCl₂-P, Citrate-P, and Enzyme-P contents (P<0.05). Under the conditions of biochar addition, N addition significantly increased rhizosphere soil CaCl₂-P, Citrate-P contents, and their proportions, but significantly decreased soil pH (P<0.05). There was a significant negative correlation between soil pH and CaCl₂-P or Citrate-P content in the rhizosphere soil (P<0.05). The activity of acid phosphatase was a key driver affecting the content of Enzyme-P. In summary, biochar addition can alleviate N-induced P limitation by increasing soil P availability. These findings provide a scientific reference for the sustainable management of Moso bamboo forests under the context of global change.

Key words: Moso bamboo, phosphorus fraction, biochar, nitrogen addition, enzyme activity