LAUSR

Heat from fire disturbance induces chemical oxidation of soil organic matter that alters the conversion of carbon (C) and nitrogen (N), which seriously influences soil structure and functions. However, the extent of oxidation depends on the fire intensity and duration, and heat penetration. In the present study, a burned area of Pinus massoniana secondary forest located in the Gaojian State Forest Farm, Zhuzhou, Hunan Province, was selected to conduct an experiment of the effects of fire disturbance on microbial activity and N mineralization of forest soil. The experiment was conducted in a completely randomized design based on two kinds of soil, three different temperatures, and three soil water potentials, with each treatment replicated three times. A variance analysis was performed on the data. The results showed the concentration of inorganic N and initial soil organic matter content were positively correlated with fire intensity. Shortly after fire disturbance, soil C and N concentration were high, but microbial biomass C and potentially mineralized nitrogen (PMN) were low, and temperature and soil water potential had no significant effect on the basic respiration. PMN loss was observed in the unheated control soils of fire disturbance compared with soils not exposed to fire. When soil temperature reached 160°C, it resulted in only a modest increase in PMN concentrations in the soil not previously exposed to fire. If soil temperature exceeded 160°C, the PMN content fluctuated, and then increased rapidly. A soil temperature of 350°C resulted