Responses of soil phosphorus availability to nitrogen addition in a legume and a non-legume plantation

Elevated nitrogen (N) deposition can alter the composition and availability of soil phosphorus (P) and thus affect long-term plant growth. However, it remains elusive whether this effect differs between legume and non-legume forest ecosystems, which have distinctly different abilities to use N and P. In this study, soil P fractions were measured in a legume (Acacia auriculiformis) and a non-legume (Eucalyptus urophylla) plantation in subtropical China, after four-years of N addition. Results showed that the concentrations of soil total P, total Po, and NaOH-Pi (Po and Pi are organic and inorganic P, respectively) were significantly higher, but soil NaHCO3-Po was significantly lower, in the legume plantation compared to the non-legume plantation. Nitrogen addition significantly decreased soil labile P fractions (i.e. NaHCO3-Pi and NaHCO3-Po) in the legume plantation, but they did not change in the non-legume plantation. In contrast, intermediate P fractions (i.e. NaOH-Pi and NaOH-Po) significantly increased with N addition in the legume plantation, but only NaOH-Po experienced a small increase in the non-legume plantation. The recalcitrant P fractions were not significantly influenced by N addition in either plantation. Due to the greater decrease in labile P in the legume plantation, our results suggest that N deposition may lead to greater P limitation in legume plantations compared to non-legume plantations.