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.