Soil Urease Properties Under Different Forests In Beijing Mountain Area

The soil samples from 0～0.2 m, 0.2～0.4 m and 0.4～0.6 m layers in five broad-leaved plantations (Betula dahurica, Robinia pseudoacacia, Castanea mollissima, Quercus dentata, mixed Betula platyphylla-Populus davidiana) and five coniferous plantations (Pinus tabulaeformis, P. bungeana, P. tabulaeformis natural secondary forest, Larix principis-rupprechtii, Platycladus orientalis) and Vitex negundo plantation were taken to study the soil urease activities, kinetic and thermodynamic properties, and to analyze the relationship between those properties and the soil physical and chemical properties, by measuring the urease activities and measuring NH3-N released in reactions when the substrate concentration, reactive time and temperature changed so as to figure out the kinetic and thermodynamic parameters, and by analyzing correlation, partial correlation, and principal component. The results showed that the urease activities changed, and the kinetic and thermodynamic parameters of urease in different forest soils changed when the reactive temperature and soil depth increased. The changes reflected different kinetic properties, including urease content, the formation of urease-urea chelate and urease-catalyzed reaction rate, and different thermodynamic properties, including potential barrier to be overcome, free energy needed and the order in the system during the formation of urease-urea. The kinetic and thermodynamic properties of urease from 0～0.2 m samples varied in different plantations. The highest urease content, the strongest affinity between urease and urea, the lowest potential barrier, the biggest increase of the order in the system and the highest reaction rate in the urease-catalyzed reactions were found in Betula platyphylla-Populus davidiana mixed plantation and Larix principis-rupprechtii plantation, while totally opposite results were found in the Castanea mollissima plantation and P. tabulaeformis natural secondary forest except not the lowest urease content. the differences about those properties were found in the other plantations. Inaditon, the relationship among that the soil urease activities, kinetic and thermodynamic properties, the soil physical, and chemical properties wer close. The soil urease activities, V_max(37℃), K(37℃), and△G(310K) played important roles in the differences of soil systems.