Soil microbial community responding to moderately elevated nitrogen deposition in a Japanese cool temperate forest surrounded by fertilized grasslands

To examine the hypothesis that the soil microbial community in a nitrogen (N) limited forest responds to moderately elevated N deposition (< 10 kg ha(-1) yr(-1)), correlations between N deposition and soil microbial properties were analyzed in a cool temperate forest surrounded by normally fertilized pasture grasslands in northern Japan. Three experimental plots were established in forest edges adjacent to the grasslands, and the other three plots were in forest interiors at least 700 m away from the grasslands. N deposition in each plot was measured from May to November 2018. In August 2018, we collected litter and surface soil samples from all plots to measure net N mineralization and nitrification rates as indicators of microbial activity, and microbial biomass and various gene abundances (i.e., bacterial 16S rRNA gene, fungal ITS region, and bacterial and archaeal amoA genes) as indicators of microbial abundance. N deposition in forest edges was 1.4-fold greater than that in forest interiors, whereas maximum N deposition was 3.7 kg ha(-1). N deposition was significantly correlated with net N mineralization and nitrification rates and 16S rRNA and bacterial amoA gene abundances. Microbial community structures analyzed for bacterial 16S rRNA gene and fungal ITS region amplicons were different between litter and soil samples but were similar between the forest edge and interior, although this analysis was made only for single pair of the two plots in the forest edge and interior. N deposition was also correlated with the soil C/N ratio and nitrate and ammonium contents. Thus, it was suggested that some soil microbial activities and abundances in an N limited forest likely responded to moderately elevated N deposition. These findings provide primary information on soil microbial response to moderately elevated N deposition.