Content of Soluble Nitrogen and Activities of Nitrogen Metabolism Enzymes in Soil in Response to Temperature Changes

The dynamic changes on the soluble nitrogen pool and nitrogen metabolism enzymes in soil as the environmental temperature was altered in a humidity-controlled incubation chamber were studied. The results showed that (a) the NO₃^--N in soil increased within 58 d after cultivation, and peaked between 48^th and 58^th d followed by a continuous decline; while NH₄⁺-N decreased initially and stabilized after 73 d, and SON fluctuated with a maximum on the 48^th d; (b) NO₃^--N increased upon increasing temperature with a significant correlation, but NH₄⁺-N had an opposite trend with a significant inverse correlation with the temperature; whereas, SON significantly correlated with the increasing temperature only in the mid-and late-stages; and, (c) the urease activity fluctuated during the entire incubation; the protease activity was higher in the initial and mid-than the late stage; the activity of asparagine enzyme increased initially but declined afterward, while that of the glutaminase enzyme increased continuously in the course of the test; and, within the testing range, the temperature induced little effect on the urease activity, but significantly affected the protease, asparaginase and glutaminase in a certain sampling times.