Abstract: Soil microorganisms are key drivers of ecological processes such as nutrient cycling. However, our understanding of how soil microbes respond to elevated atmospheric nitrogen (N) deposition in Chinese subtropical evergreen broadleaved forests is still very limited. A field N addition experiment was conducted to study the responses and influencing factors of soil microbes to simulated N deposition in the Dinghushan Biosphere Reserve (DHSBR), Guangdong, China. Surface soil samples (0-10 cm) under four N treatment levels (0 (CK), 35 (LN), 70 (MN) and 105 (HN) kg^-1·hm^-2·a^-1) were collected in the dry (January) and wet (July) seasons. Soil microbial community structure was analyzed using the phosphorous fatty acids (PLFAs) method. Our results showed that: (1) N addition significantly enhanced the PLFAs biomass of the dominant microbial groups including bacteria, actinomycetes and fungi, with bacteria being the most abundant group; (2) There were obvious seasonal differences in microbial responses to N addition. Although the PLFAs were always higher in the dry than wet season, the moderate N addition (MN) treatment had the largest impact on microbial biomass in the dry season while the high N addition (HN) had the largest impact in the wet season; (3) Both N addition and season imposed significant impacts on microbial community composition. Dissolved organic carbon content and soil water content were the most influencing factors regulating microbial community in the dry season, while soil pH and available N and P contents played the important role in the wet season. Our results indicate that elevated N deposition in the subtropical China may exert seasonally differentiated impacts on soil microbial communities, and thus key ecological processes. A comprehensive consideration of N deposition level, season, and soil microbial responses is critically important when studying the effects of atmospheric N deposition on the evergreen broadleaved forest in the region.

Key words: bioprotection, microorganisms, lichens, biocides prevention