Abstract
ABSTRACT 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.
Highlights
IntroductionNitrogen deposition (deposition of nitrate (NO3−) and ammonium (NH4+) ions) increased by anthropogenic usage of excess nitrogen fertilizers and fossil fuels (Galloway et al 2004) is still a major environmental concern in global scale (Decina, Hutyra, and Templer 2019; Dentener et al 2006; Kanakidou et al 2016; Reay et al 2008), while reducing trends in nitrogen deposition are observed in some areas of Europe and North America as a result of efforts to mitigate anthropogenic nitrogen oxide emissions (Gilliam et al 2019; Schwede et al 2018; Waldner et al 2014)
In order to capture reliable responses of forest ecosystems against changing nitrogen status, we need to know more about the effects of moderately elevated nitrogen deposition (< 10 kg N ha−1 y−1) on nitrogen-limited forest ecosystems
We focused on the relationship between spatially varied nitrogen deposition and soil microbial properties within a cool temperate forest in the eastern area of Hokkaido, Japan
Summary
Nitrogen deposition (deposition of nitrate (NO3−) and ammonium (NH4+) ions) increased by anthropogenic usage of excess nitrogen fertilizers and fossil fuels (Galloway et al 2004) is still a major environmental concern in global scale (Decina, Hutyra, and Templer 2019; Dentener et al 2006; Kanakidou et al 2016; Reay et al 2008), while reducing trends in nitrogen deposition are observed in some areas of Europe and North America as a result of efforts to mitigate anthropogenic nitrogen oxide emissions (Gilliam et al 2019; Schwede et al 2018; Waldner et al 2014). Increased nitrogen deposition variously affects forest ecosystems by altering biodiversity, productivity, biogeochemical cycles, energy dynamics, and so on (Chiwa et al 2018; Groffman et al 2018; Janssens et al 2010; Jia et al 2020; Reay et al 2008; Zhang, Chen, and Ruan 2018) These effects of nitrogen deposition on forest ecosystems have been investigated mostly by manipulation experiments with more than 20 kg N ha-1 yr-1 of nitrogen addition (Janssens et al 2010; Jia et al 2020; Zhang, Chen, Ruan, 2018). In order to capture reliable responses of forest ecosystems against changing nitrogen status, we need to know more about the effects of moderately elevated nitrogen deposition (< 10 kg N ha−1 y−1) on nitrogen-limited forest ecosystems
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