Responses of soil microbial biomass and carbon source utilization to simulated nitrogen deposition and drought in a Cunninghamia lanceolata plantation

Abstract

Chinese fir (Cunninghamia lanceolata) plantation is a dominant forest type and carbon sink in the subtropical region in China. An experiment with simulated nitrogen deposition (addition of 40 kg N·hm-2·a-1) and drought (50% of precipitation exclusion, PE) was established in Chinese fir plantation in 2018. Soil samples (0-15 cm) were collected in summer (July 2020) and winter (January 2021). Soil microbial biomass, colony forming units (CFUs) and carbon source utilization were determined through phospholipid fatty acids (PLFAs), plate count, and Biolog methods, respectively. The results showed significant seasonal variations of PLFAs-related microbial biomass and composition. Soil bacterial and fungal CFUs tended to be decreased by nitrogen addition or precipitation exclusion treatment, and bacterial CFUs were more sensitive to the two treatments than fungal CFUs. Soil microbial function (i.e. carbon source utilization) was not affected by nitrogen addition, but significantly decreased by precipitation exclusion. There was a significant positive correlation between bacterial CFUs and microbial function, indicating the crucial roles of culturable bacteria in microbial carbon transformation. Our results highlight the critical effects of nitrogen deposition and 50% reduced precipitation on microbes in topsoil of fir plantation, with implications for unraveling soil microbial ecological function of subtropical forest ecosystem under global changes in future.