Effect of long-term nitrogen addition on the kinetics of phosphatases in a subtropical forest in southern China.

Numerous studies have explored the effects of nitrogen (N) addition on the maximum rate of substrate conversion (V max) of phosphatase activity, whereas how N fertilization affects the substrate affinity (the Michaelis constant, K m) of phosphatases is not well understood. Here, we examined a recently-proposed novel hypothesis suggesting that N addition enhances the adaptability of soil microorganisms to low phosphorus (P) conditions by both increasing phosphatase abundance (i.e., increasing the V max of phosphatases) and enhancing the substrate-binding affinity of phosphatases (i.e., diminishing the K m of phosphatases). Contrary to the hypothesis, our study found that no level of N addition led to changes in either V max or K m of phosphatases in our study site. Furthermore, we observed a positive correlation between V max and K m , which challenges the proposed hypothesis, as this positive relationship contradicts the condition suggested by the hypothesis that the adaptive response of increasing phosphatase abundance (higher V max) should be associated with increased substrate affinity (lower K m). In conclusion, the present study indicates that N addition does not necessarily enhance the substrate affinity of phosphatases. • We examined a recently suggested hypothesis that N addition enhances both production and substrate affinity of phosphatases. • N addition did not change the substrate affinity of phosphatases. • The positive correlation between V max and K m challenges the novel hypothesis. [ABSTRACT FROM AUTHOR]