Xinyu Zhang, Yang Yang, Chuang Zhang, ShuliNiu, Hao Yang, Guirui Yu, Huimin Wang, EvgeniaBlagodatskaya, YakovKuzyakov, DashuanTian, Yuqian Tang, Shuang Liu, Xiaomin Sun
Global changes including increases in nitrogen (N) deposition and phosphorus (P) fertilization may cause changes in the nutrient demands of plants and microbes. Soil phosphatase enzymes that are produced by plants and microbes transform a significant portion of organic P to P that is available for uptake by plants and microbes. Previous studies demonstrated that the maximum enzyme activity followed an economic principle, i.e. microbes preferentially allocated carbon and nutrients towards the acquisition of whatever resource was most limiting their growth. This suggests that the maximum phosphatase activity may therefore increase when N is added and decrease when P is added. However, phosphatase mainly operates under non-saturated conditions and cannot reach its maximum levels of activity in soils. To date, the changes in phosphatase activity for different substrate contents that might occur when N and P are added have not been reported for forest soils with different P concentrations. To answer these questions, we examined the phosphatase activities for different substrate contents after adding N and P to forest soils with different P concentrations.
Our results showed that, when N was added, the phosphatase activity for different substrate contents increased, and the substrate demand increased. Therefore, the efficiency of the phosphatase catalytic reactions in P-rich and P-poor soils did not change when N was added. As expected, when P was added to P-poor soils, the efficiency of the phosphatase catalytic reactions decreased as inorganic P inhibited the phosphatase activity for different substrate contents. Remarkably, when P was added to P-rich soils, the phosphatase activity for different substrate contents and the substrate demand both increased, but the efficiency of the phosphatase catalytic reactions did not change. Our results show that phosphatase activity for different substrate contents responded contrarily to P additions in P-rich and P-poor forest soils. The results also suggest that phosphatase secretion might increase, and P limitations might decrease, if subjected to long-term N deposition.
Image caption: The Korean Pine mixed Mongolian Oak forest in Changbai Mountain in temperate climate zone. Photograph provided by authors.