Abstract
BackgroundChina’s terrestrial ecosystems have been receiving increasing amounts of reactive nitrogen (N) over recent decades. External N inputs profoundly change microbially mediated soil carbon (C) dynamics, but how elevated N affects the soil organic C that is derived from microbial residues is not fully understood. Here, we evaluated the changes in soil microbial necromass C under N addition at 11 forest, grassland, and cropland sites over China’s terrestrial ecosystems through a meta-analysis based on available data from published articles.ResultsMicrobial necromass C accounted for an average of 49.5% of the total soil organic C across the studied sites, with higher values observed in croplands (53.0%) and lower values in forests (38.6%). Microbial necromass C was significantly increased by 9.5% after N addition, regardless of N forms, with greater stimulation observed for fungal (+ 11.2%) than bacterial (+ 4.5%) necromass C. This increase in microbial necromass C under elevated N was greater under longer experimental periods but showed little variation among different N application rates. The stimulation of soil microbial necromass C under elevated N was proportional to the change in soil organic C.ConclusionsThe stimulation of microbial residues after biomass turnover is an important pathway for the observed increase in soil organic C under N deposition across China’s terrestrial ecosystems.
Highlights
Atmospheric nitrogen (N) deposition, primarily originating from fossil fuel combustions and artificial fertilizer applications, has increased more than tenfold over the past century (Fowler et al 2013) and has currently reached an average of 20.4 kg N/ha/yr over China’s terrestrial ecosystems (Yu et al 2019)
Data compilation The experiments to determine the concentrations of soil microbial necromass C or proxies under N addition were screened by the Web of Science and China National Knowledge Infrastructure databases
Changes in soil microbial necromass C and biomass C after N addition The concentrations of total microbial, fungal, and bacterial phospholipid fatty acids (PLFAs) were increased by 25.7%, 32.2%, and 17.4%, respectively, after N addition (Fig. 2a)
Summary
Atmospheric nitrogen (N) deposition, primarily originating from fossil fuel combustions and artificial fertilizer applications, has increased more than tenfold over the past century (Fowler et al 2013) and has currently reached an average of 20.4 kg N/ha/yr over China’s terrestrial ecosystems (Yu et al 2019). Increasing evidence has indicated that atmospheric N deposition has the potential to increase soil organic C storage by multiple pathways (Janssens et al 2010; Liu and Greaver 2010). N is a limiting nutrient for plant growth in most terrestrial ecosystems, so N addition can profoundly facilitate plant growth and increase plant C input (LeBauer and Treseder 2008; Song et al 2019). Elevated N increases plant lignin content (Liu et al 2016), and high lignin content has been found to reduce litter decomposition under N addition (Knorr et al 2005), increasing the amounts of litter materials on the soil surface without being decomposed (Zak et al 2008). External N inputs profoundly change microbially mediated soil carbon (C) dynamics, but how elevated N affects the soil organic C that is derived from microbial residues is not fully understood. We evaluated the changes in soil microbial necromass C under N addition at 11 forest, grassland, and cropland sites over China’s terrestrial ecosystems through a meta-analysis based on available data from published articles
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