The dynamic and thermodynamic characteristics of soil reactions catalyzed by soil enzymes under long-term fertilization in Loess Plateau

Soil enzyme is a sensitive indicator of soil fertility condition.The dynamic and thermodynamic characteristics of soil enzymes can illustrate the enzyme catalyzed soil biochemical processes and explain the changing mechanisms of soil fertility.In this paper,the dynamic and thermodynamic parameters of soil reactions catalyzed by soil enzymes were analyzed for the soils under 25 years' continuous fertilization.The objective of this research was to reveal the effects of long-term fertilization on soil fertility from the aspects of soil enzymes.The results showed that long-term fertilization increased Vmax,Vmax/Km and k, but decreased Ea,△G,△H and △S,indicating that fertilization could improve the velocity of enzymatic reaction,decrease the free energy for activation,and therefore boost the cycling process of soil nitrogen and phosphorus.The correlation analysis between dynamic and thermodynamic parameters of enzymatic catalyzed reaction and soil properties suggested that dynamic and thermodynamic parameters of enzymatic catalyzed reaction mainly depended on soil chemical properties and the soil fertility evaluation index system based on dynamic and thermodynamic parameters could be used to evaluate soil fertility.The results from this study further implied that UVmax,PKm and PVmax were important indices for the evaluation of soil fertility.