[Effect of Nitrogen Deposition on Soil Microbial Community Structure Determined with the PLFA Method Under the Masson Pine Forest from Mt. Jinyun, Chongqing].

Nitrogen deposition increases the productivity of forest-land, yet may cause environmental damage, while soil microorganisms are sensitive to the ecological environment. The objective of this study was to investigate the effects of nitrogen deposition on soil microbial communities and the relationship among soil microbial communities, soil temperature, soil moisture and the concentration of nitrogen deposition in the Masson pine forest. The results might provide a reference for further study on the effects of nitrogen deposition on forest ecosystem of Masson pine. From May 2014 to June 2015, three nitrogen application treatments and the control treatment were set up:low nitrogen [N,20 g·(m·a)], moderate nitrogen [N, 40 g·(m·a)], high nitrogen [N, 60 g·(m·a)] and control treatment [N, 0 g·(m·a)] in the Masson pine forest. Soil microbial community structure, soil temperature and soil moisture were measured by phosphorus lipid fatty acids (PLFAs) and automated soil CO exchange station. The results showed that:1 Seasonal variation had a remarkable effect on soil bacteria, fungi, actinomycetes and the total PLFA(<0.05), all kinds of soil microorganisms had the highest amounts in spring and the lowest in winter. In different seasons, the response of different soil microorganisms to nitrogen deposition was different. Generally, nitrogen deposition decreased soil microorganisms in spring and autumn, while in summer and winter, nitrogen deposition had a positive effect on soil microorganisms. 2 Nitrogen deposition had a significant effect on soil microbial community structure(<0.05). In spring and summer, low nitrogen and moderate nitrogen decreased the soil microbial richness index and diversity index, yet increased the evenness index. In the autumn and winter, low nitrogen and moderate nitrogen promoted the soil microbial richness index, diversity index and evenness index. In all four seasons, nitrogen deposition reduced the soil microbial richness index, diversity index and evenness index. 3 Correlation analysis showed that the concentration of nitrogen deposition had a very significant negative correlation with soil bacteria (<0.01), and a significant negative correlation with total PLFA (<0.05). Soil temperature had a significant negative correlation with soil actinomycetes. Soil moisture had a significant positive correlation with bacteria and total PLFA. In conclusion, soil microorganisms of Masson pine forest were mainly influenced by soil moisture and less affected by soil temperature in Jinyun Mountain. Nitrogen deposition had a significant effect on microbial community structure and diversity.