Phosphorus uptake in four tree species under nitrogen addition in subtropical China

Atmospheric N deposition is a serious problem in subtropical China where N is present in large amounts but P is deficient. Several studies hypothesized that N₂ fixers can overcome phosphorus limitation by trading fixed N₂ for soil phosphorus. In order to know whether N₂ fixers could invest fixed N₂ in extracellular phosphatase production and could stimulate arbuscular mycorrhizal fungi (AMF) to acquire soil P in N-rich subtropical China, an open-air greenhouse experiment was carried out. Two N₂ fixers (Acacia mangium and Ormosia pinnata) and two non-N₂ fixers (Schima superba and Pinus massoniana) were exposed to three levels of N addition: 5.6 kg ha^-1 a^-1 (ambient N), 15.6 kg ha^-1 a^-1 (middle N), and 20.6 kg ha^-1 a^-1 (high N). We found that the capacity of plants to acquire soil P in N-rich subtropical China is species specific. The higher P uptake rates were found for N₂ fixers than non-N₂ fixers under N addition, which were related to the greater soil APA and higher AMF (p < 0.01) in the soil of N₂ fixers. However, with time, high N addition decreased more significant quantities of soil microbial phospholipid fatty acids (PLFAs) in the soil of N₂ fixers than that of non-N₂ fixers (p < 0.05). We conclude that N₂ fixers have higher P uptake capacity than non-N₂ fixers under ambient N deposition in subtropical China. However, continuing N deposition in the future might affect P uptake ability of N₂ fixers as high N addition would decrease soil microbial PLFAs of N₂ fixers.