Climate warming and nitrogen(N)deposition change ecosystem processes,structure,and functioning whereas the phosphorus(P)composition and availability directly influence the ecosystem structure under conditions of N deposition.In our study,four treatments were designed,including a control,diurnal warming(DW),N deposition(ND),and combined warming and N deposition(WN).The effects of DW,ND,and WN on P composition were studied by31P nuclear magnetic resonance(31P NMR)spectroscopy in a temperate grassland region of China.The results showed that the N deposition decreased the soil pH and total N(TN)concentration but increased the soil Olsen-P concentration.The solution-state31P NMR analysis showed that the DW,ND and WN treatments slightly decreased the proportion of orthophosphate and increased that of the monoesters.An absence of myo-inositol phosphate in the DW,ND and WN treatments was observed compared with the control.Furthermore,the DW,ND and WN treatments significantly decreased the recovery of soil P in the NaOH–EDTA solution by17%–20%.The principal component analysis found that the soil pH was positively correlated with the P recovery in the NaOH–EDTA solution.Therefore,the decreased soil P recovery in the DW and ND treatments might be caused by an indirect influence on the soil pH.Additionally,the soil moisture content was the key factor limiting the available P.The positive correlation of total carbon(TC)and TN with the soil P composition indicated the influence of climate warming and N deposition on the biological processes in the soil P cycling.
Alpine tundra ecosystems have specific vegetation and environmental conditions that may affect soil phosphorus(P) composition and phosphatase activities. However, these effects are poorly understood. This study used Na OH-EDTA extraction and solution31 P nuclear magnetic resonance(NMR) spectroscopy to determine soil P composition and phosphatase activities, including acid phosphomonoesterase(Ac P), phosphodiesterase(PD) and inorganic pyrophosphatase(IPP), in the alpine tundra of the Changbai Mountains at seven different altitudinal gradients(i.e., 2000 m, 2100 m, 2200 m, 2300 m, 2400 m, 2500 m, and 2600 m). The results show that total P(TP), organic P(OP), OP/TP, Na OH-EDTA extracted P and AcP, PD, and IPP activities over the altitude range of 2500–2600 m are significantly lower than those below 2400 m. The dominant extracted form of P is OP(73%–83%) with a large proportion of monoesters(65%–72%), whereas inorganic P is present in lower proportions(17%–27%). The activity of Ac P is significantly positively correlated with the contents of soil OP, total carbon(TC), total nitrogen(TN), and TP(P < 0.05), indicating that the Ac P is a more sensitive index for responding P nutrient storage than PD and IPP. Soil properties, P composition, and phosphatase activities decrease with increased altitude and soil p H. Our results indicate that the distribution of soil P composition and phosphatase activities along altitude and Ac P may play an important role in P hydrolysis as well as have the potential to be an indicator of soil quality.
