Yue Li1, Yinghui Liu1, Shanmei Wu1, Cheng Nie1, Nicola Lorenz2, Nathan R. Lee2 and Richard P. Dick3, (1)Beijing Normal University, Beijing, China (2)The Ohio State University, Columbus, OH (3)406C Kottman Hall, 2021 Coffey Road, Ohio State University, Columbus, OH
Carbon (C) and nitrogen (N) cycling in soil during microbial decomposition is well studied, yet the mechanism underlying the response of microbial C utilization to the presence of N still remains an open question. This study was designed to determine the effect of long-term N fertilization on grassland microbial communities, and to explore if the alteration of labile C utilization of microbial communities was affected by N. A 35-day multi-factorial incubation experiment with three N fertilization rates 0, 4, or 16 g N m-2 yr-1 (applied as urea) and one C substrate application, 0.4 mg 13C glucose g-1 soil was conducted using a temperate grassland soil. A treatment without glucose addition served as a control. Long-term N addition was found to significantly reduce fungal biomass but increased the biomass of gram-positive bacteria. N addition showed to strengthen the role of gram-positive bacteria and actinomycetes, but reduced the contribution of gram-negative bacteria and fungi in 13C utilization. In addition, the dynamics of gram-negative bacteria and fungi in13C utilization during the decomposition process were also regulated by N addition. The functioning of saprophytic fungi in this temperate grassland indicated the functional diversity in this community. Decomposition theories such as nutrient stoichiometry and N mining were both confirmed in this study, as N mining was least prominent in soil with high N enrichment, while optimal nutrient ratio existed when labile C was added in soil under low N enrichment. There was no significant difference of soil C among N treatments in the temperate grassland. It might be due to the tradeoff between microbial C utilization in labile C and SOM.