Effects Of Simulated Nitrogen Deposition On Soil Microoganism And Enzyme Activity In Natural Forest In Rainy Area Of Western China

Since the industrial revolution, the increasing atmospheric nitrogen deposition has been changing the structure and functions of terrestrial ecosystems, Soil microbes and enzyme activity as an active participant of material circulation and energy conversion in ecological system, is extremely sensitive to the change of environment. It means that atmospheric nitrogen deposition may affect soil microbes and enzyme activity, so influence the material cycle and energy conversion process of forest ecosystems. But the research of the effects of nitrogen deposition on forest soil microbes and enzyme activity mainly concentrated in the temperate forests, and the response of atmospheric N deposition on the soil microbes and enzyme activity of subtropical forest ecological system is relatively few, mainly in plantation, mainly in the plantation. To investigate the effects of simulated nitrogen (N) deposition on the soil microbial quantity?microbial biomass and enzyme activity in the 0-10 cm and 10-20 cm soil layers, a one-year field experiment following N addition treatments was conducted in a natural evergreen broad-leaved forest in a rainy area of Western China. Beginning November 2013, we conducted a field experiment that included four treatments:0,50,150 and 300 kg N·hm-2·a-1 as the control (CK), low (L), medium (M), and high (H) nitrogen deposition, respectively. Every 15 days, NH4NO3 was added to the N-treated plots. The results indicated that:(1) Nitrogen deposition has not changed the original vertical distribution pattern of bacteria, fungi and actinomycetes, the number of bacteria, fungi and actinomycetes show that 0-10 cm soil layer is greater than 10-20 cm soil layer in a natural evergreen broad-leaved forest in a rainy area of Western China. The quantity of soil bacteria, fungi and actinomycetes are had obvious seasonal dynamics,0-10 cm and 10-20 cm soil layer show that the fall is highest and summer is lower. Compared with the CK treatment, M and H conducts significantly increased the number of fungi in the 10-20 cm soil layer in summer, indicates a suitable amount of nitrogen deposition can effectively alleviate the nitrogen limiting state of soil fungi in summer.(2) Nitrogen deposition inhibition the number of bacteria in the 0-10cm and 10-20cm soil layer, the inhibition effect enhanced with the increase of the amount of nitrogen deposition; and reduce the number of fungi in the 0-10cm soil layer, but it is had no obvious regularity between decreased and amount of nitrogen deposition. The effects of Nitrogen deposition on the quantity of actinomyces in the 0-10 cm soil layer show that promoting first again inhibiting. L and M conducts increased the number of actinomycetes, H conducts reduced the number of actinomycetes; promoted the number of actinomycetes in the 10-20 cm soil layer, M conduct with the largest role in promoting. The effects of nitrogen deposition on the quantity of soil microbial weakened along with the increase of soil depth.(3) Nitrogen deposition has not changed the original vertical distribution pattern of the MBC and MBN in the 0-10 cm and 10-20cm soil layer, and the content of MBC and MBN in the 0-10 cm soil layer is greater than 10-20cm soil layer in a natural evergreen broad-leaved forest in a rainy area of Western China. The content of soil MBC and MBN have obvious seasonal dynamic, in the 0-10 cm and 10-20 cm soil layer show that the fall is highest and summer is lower. Compared with the CK treatment, L and M conducts significantly increased the content of MBC in the 10-20cm soil layer in the summer.(4) Nitrogen deposition decreased the content of MBC and MBN in the 0-10 cm soil layer. Decent degree increased with increasing the amount of nitrogen deposition. L and M conducts had no significant effect for the content of soil MBC and MBN in the 10-20 cm soil layer. H conducts significantly reduced the content of soil MBC. The influence of nitrogen deposition on MBC and MBN content weakened with the increase of soil depth.(5) There was no significant difference of soil microbial biomass C/N between different soil layer, show that the ratio had no significant difference between soil fungi and bacteria. Compared with other seasons,the soil microbial quantity in winter is biggest, which indicates that the fungi are much more advantages than bacteria in winter. The fluctuation range of soil microbial biomass C/N is respectively 10.58?11.19 and 9.62?12.20 in the 0-10 cm and 10-20cm soil layer, which indicates that the fungus hold advantage In the soil microbial community in a natural evergreen broad-leaved forest in a rainy area of Western China. H conduct reduced the soil microbial biomass C/N, make the microbial community dominated into bacteria in the food web in the 0-10 cm soil layer.(6) The activity of sucrase?cellulase?urease?acid phosphatase?catalase?peroxidase? polyphenol oxidase in 0-10 cm soil layer all were greater than 10-20 cm soil layer in a natural evergreen broad-leaved forest in a rainy area of Western China, nitrogen deposition has not changed the original vertical distribution pattern.The seven kinds of soil enzyme activity of the every conducts have obvious seasonal dynamics, and they were consistent in the 0-10 cm and 10-20 cm soil layer. The activity peaks of cellulose enzyme appeared in the spring, the activity peak of catalase and acidic phosphatase appeared in the summer, the activity peak of sucrase and urease appeared in the autumn, the activity peak of peroxidase activity and polyphenol oxidase appeared in the winter. In comparison with CK, M conduct changed the activity peak of soil acid phosphatase, make it appeared in the autumn,and changed the activity peak of soil catalase in the 10-20 cm soil layer, to make it appeared during the spring and autumn.(7) Nitrogen deposition had no significant effect on the activity of cellulose enzyme, L conduct increased to the activity of soil urease and acidic phosphatase; M conduct promoted the activity of urease and Inhibits the activity of sucrase?catalase and polyphenol oxidase; H conduct inhibited the activity of sucrase?urease?catalase? peroxidase and polyphenol oxidase in the 0-10cm soil layer. Nitrogen deposition, especially high nitrogen deposition significantly inhibited the carbon cycle related enzyme activity and slow down the soil carbon cycle, so increased the soil store capacity of difficult decomposition of organic matter. Nitrogen deposition had no obvious effect on the activity of sucrase?urease?cellulase?acid phosphatase?peroxidase?polyphenol oxidase in the 10-20cm soil layer. M and H conducts reduced the activity of catalase.