Long-term nitrogen addition facilitates phosphorus uptake by the roots of Phyllostachys pubescens

We conducted a field nitrogen addition experiment in a subtropical natural Phyllostachys pubescens forest taking ammonium nitrate as nitrogen source. There were three nitrogen addition levels: 0, 20, and 80 kg N·hm^-2·a^-1, corresponding to the control, low nitrogen, and high nitrogen treatments, respectively. In the ninth year of treatments, we collected samples of surface soil from 0 to 15 cm to determine soil basic chemical properties, microbial community composition, acid phosphatase activity, and analyzed leaf nitrogen and phosphorus contents, leaf phosphorus fractions, and fine root biomass and phosphorus content in P. pubescens. We explored the effects of nitrogen addition on plant phosphorus-utilization and -acquisition strategies of P. pubescens, as well as their correlations with environmental factors. The results showed that both low and high nitrogen additions significantly increased foliar nitrogen and phosphorus contents, but did not change foliar nitrogen-to-phosphorus ratio. Only the treatment of high nitrogen addition significantly increased the contents of metabolic phosphorus, nucleic acid phosphorus, and structural phosphorus in the leaves, without altering the proportion of each phosphorus fraction. On average, low and high nitrogen additions significantly increased soil available phosphorus content by 31.4% and fine root phosphorus content by 28.9%, but significantly decreased soil organic phosphorus content by 28.2%. Fine root phosphorus content was significantly positively correlated with fine root biomass, the abundance of soil arbuscular mycorrhizal fungi, and available phosphorus content. In summary, P. pubescens allocated more carbon to belowground under long-term nitrogen addition, thereby enhanced root phosphorus uptake.