Impacts Of Nitrogen Deposition On Soil Carbon Content And Activity Of Soil Cellulase Enzymes In The Chinese Fir Plantation

The global carbon cycle has been impacted by human society. Forest are the main terrestrial ecosystems which loading 46.3% of the total carbon pool in the earth land, and forest vegetation carbon pools maintained as high as 77.0% of the terrestrial vegetation carbon pools, so the cycle of the forest carbon are the world's most important carbon cycle, and it plays an important role in maintaining global ecological security and the sustainable development of human society. With the development of human society, the negative effects of growing nitrogen deposition on global carbon cycle became more and more serious, so it is concerned by the international community, Researching the effects of nitrogen deposition on carbon pools of understory of the Chinese fir plantation, and carbon concense of soil in the forest, and activity of cellulase in soil from the forest, not only can make up China's deficiencies in the areas of the study, as well as making a base for studying the global change. In this paper, in order to investigate the response of the above three parameters of the ecological system to increased nitrogen deposition, a field experiment was conducted in a 12-year-old Chinese fir plantation forest in Sanming, northwestern Fujian. Nitrogen loadings were designed at four levels as N0, N1, N2, and N3, at the doses of 0,60,120 and 240 kg N hm-2 yr-1, respectively, with three replicates in each treatment. Based on four or six years of manipulation, the research results responding to nitrogen loading are as follows:1.Effects of nitrogen deposition on content of organic matters in the soil of forestAfter 6 years of simulated nitrogen deposition treatment, soil organic matter content in chinese fir plantation is in the order of:N2>N1>N0>N3. Compared with the control N0 treatment, N1 treatment plots increased soil organic matter content by 7.08%, N2 treatment plots increased soil organic matter content by 21.84%, while N3 treatment plots reduced soil organic matter content by 4.21%. After analysis of variance, organic matter content show no significant difference between N1, N3 treatment plots and the N0 treatment plot, but the soil organic matter in N2 treatment plot show significant differences compared to that in the N0 treatments. So we can conclude that N2 treatment increased the soil organic matter content, and N3 decreased soil organic matter content, and N1 treatment have no affection on the soil organic matter content2. Effects of nitrogen deposition on activity of cellulase enzymes in the soil of forestAfter 6 years of simulated nitrogen deposition treatment in Chinese fir plantation, compared with the control NO, filter paper activity of cellulase enzymes in soil from plots treated by Nl decreased 14.43%, N2 treatment decreased 16.46%, while N3 increased 2.03%. Variance analysis of soil filter paper activity show that, N1, N2 treatment have a greater difference from N0, but N3 treatment have little difference from N0; Compared with the control N0, EC3.2.1.91 activity in soil from plots treated with N1 increased to 131.25%, and N2 treatment increased 265.5%, while N3 treated increased 131.25%. After analysis of variance, EC3.2.1.91 activity in soil from plots treated by N1, N2, N3 treatment was significantly difference from that in the control treatment, in which N2 treatment is the most significant difference from NO.3. regression relation between soil organic matter concense and activity of cellulose enzymes of soil in forestSoil organic matter content and soil filter paper enzyme activity has a large negative correlation, the results showed that the higher activity of the soil filter paper, the lower soil organic matter content. The reason may be that, the more the filter paper activity is, more easy is the long or short sizes of fiber moleculars degraded and dissoluted in soil, resulting in the loss of soil organic matter. Soil organic matter content and soil EC3.2.1.91 activity has some degree of positive correlation, and the results show that the higher soil EC3.2.1.91 activity, higher soil organic matter content. Following may be reasons, higher is EC3.2.1.91 activity, more easy is cellulose molecules biodegraded down into the fibers of different sizes and adsorption to soil particles, resulting in the improvement of soil organic matter.4 Effects of nitrogen deposition on vegetation carbon storage of understory in Chinese fir plantationAfter four years of nitrogen deposition simulation, the carbon storage of understory herbs in stands treated by N1, N2, N3 had reduced respectively by 0.072, 0.136,0.167 t/hm2 compared to the control (NO) treatment, and the carbon storage of undergrowth in stands treated by N1, N2, N3 had reduced respectively by 0.092, 0.237,0.314 t·hm-2 compared to the control (NO) treatment. General view, after four years of nitrogen deposition simulation, the carbon storage size of understory vegetation in the stands treated with nitrogen deposition are as follows:N0> N1>N2> N3, and compared to the control treatment, the carbon storage of understory vegetation in the stands treated by N1, N2 and N3 reduced respectively by 0.164, 0.373 and 0.480t·hm-2, and respectively again, about annual reduced by 0.041,0.093 and 0.120t·hm-2 in average. When we converted the carbon storage into the amount of CO2, the reduced carbon storage of the understory vegetation in stands which treated by N1, N2 and N3 is equal to release CO2 0.151,0.342 and 0.441 t·hm-2 respectively every year. The results showed that the higher level of the nitrogen deposition is, the more vegetation carbon stock reduced in the understory of Chinese fir.