Nitrogen Mineralization In Dark Brown Forest Soils During Laboratory Incubation

Nitrogen is one of the essential elements plants need in the period of growth. In the forest ecology system, Nitrogen is usually concerned as one of the factors that restrict plants' growing, thus it affects the succession of forest communities. Nitrogen also plays an important role in the maintenance of the stability of upstage communities and keeping a constant percentage of different tree species.Nitrogen mineralization is defined as the process of transformation from organic form to inorganic form under the effect of microorganism. The organic Nitrogen is difficult for the plants to absorb, while the inorganic Nitrogen can be absorbed directly by the plants. The net Nitrogen mineralization rate is a significant index used to describe Nitrogen mineralization. This index determines the availability of Nitrogen for the plants to absorb. Nitrogen mineralization is one of the main processes of Nitrogen recycling in the ecosystem, so it has a significant meaning in indicating the function of the ecosystem and the process of Nitrogen recycling.The Dark Brown Forest Soil and the litter of surface layer in the temperate forest of our country are researched in this paper. Using the major method that is indoor aerated incubation to measure the contents of NO₃^- and NH₄⁺ in time order, we found the relationship between Nitrogen mineralization and incubation time, forest type, season, organic carbon, total Nitrogen, C/N ration, pH and so on. We can summarize the above points as following:(1) Ammoniation account for large dominance in the Nitrogen mineralization of the litter, while in the Nitrogen mineralization in the soil, nitrification takes a large percentage. Mineralization is more than solidify in the early days of the incubation, and is less than solidify in the end of the incubation during which both process are intense. As the incubation time prolonged, the Nitrogen mineralization in soil represented as mineralization larger than solidify intensified remarkably. However, there is a distinct lag mineralization in the early stage of the incubation for the reason of lack of NH₄⁺.(2) There is a distinct relationship between net Nitrogen mineralization rate and forest type. The rate of Pinus acea forest is obviously lower than that of broad leaved forest both in the litter and in the soil. The net mineralized Nitrogen content of each forest type has an obvious "mineralization-solidify" balanced period which is about 15 to 30 days. Days to reaching this period of Nitrogen in litter of Pinus acea forest are associated with the maturity of forest stand. The wildwood reaches this period firstly (14.18 days), and the next is 50a stand (15.54), and the last is 25a stand (16.64). Spruce forest is similar to broad leaved forest. The net Nitrogen mineralization rate has little relationship with forest type, behaved as stronger mineralized lag phase, lower original mineralization rate, and higher net Nitrogen mineralization rate.(3) The change trend that Nitrogen mineralization in litter and soil of each forest type in different seasons varies with incubation time is not so obvious under the same condition, however, net Nitrogen mineralization rate in the litter and soil has a distinct seasonal variation. The rate of Pinus forest is highest in summer, while that of broad leaved forest is highest in autumn. This rate of all kinds of stands is restrained to some extent. There is an evident trend in the soil that is the rate is higher in spring than in summer, and that is higher in summer than in autumn.(4) The net Nitrogen mineralization rate in the litter and soil is associated closely with organic Carbon and total Nitrogen, especially the Nitrogen that is easily to mineralize. When the carbon nitrogen ratio is lower than 25, the net Nitrogen mineralization rate has positive correlation with carbon nitrogen ratio, when this ratio is above 25, the net Nitrogen mineralization rate has negative correlation with carbon nitrogen ration.(5) During the incubation process, the pH value of soil increases, which promotes the nitrification of the soil, while the pH value of litter has no visible variation.On the basis of former research, this paper has following innovations and new view points:(1) Separating the litter from soil, then using aerobic culture to research the characteristic of nitrogen mineralization of forest soil. As we cut the relationship between litter and soil, the result can open out the real characteristic of nitrogen mineralization.(2) We found out that nitrification takes an advantage in soil, and ammoniation takes an advantage in litter. Nitrification inhibitory stage in soil results from lack of NH/.(3) In the original stage, there exists lots of NH/ for the reason that strong ammoniation in litter layer leads to the displace of NH4"1".