4.7 Article

Detecting microbial N-limitation in tussock tundra soil: Implications for Arctic soil organic carbon cycling

期刊

SOIL BIOLOGY & BIOCHEMISTRY
卷 55, 期 -, 页码 78-84

出版社

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.soilbio.2012.06.010

关键词

Arctic soils; Microbial N-limitation; N-addition; C-mineralization; Decomposition

资金

  1. Kearney Foundation of Soil Science
  2. Department of Energy Global Change Education Program Graduate Fellowship

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More than a third of the global soil organic carbon (SOC) pool is estimated to be stored in northern latitudes. While the primary regulators of microbially-mediated decomposition in physically unprotected organic soils are typically attributed to abiotic factors (e.g. temperature and moisture), in extremely nutrient-poor environments such as the Alaskan Arctic tussock tundra, evidence from field studies suggests that low N-availability may also strongly limit microbial growth, and thus the rate of SOC decomposition. However, there have been few direct tests of microbial nutrient-limitation, particularly in Arctic systems. We predicted that during the Arctic summer growing season, when both plants and microbes are competing for mineralized nutrients, N-availability in tussock tundra soil is so low that it will limit microbial biomass production, and thus decomposition potential. We tested this prediction by adding N and C to tussock tundra organic soil and tracking microbial responses to these additions. We used a combination of approaches to identify microbial N-limitation, including changes in microbial biomass, C-mineralization, substrate use efficiency, and extracellular enzyme activity. The Arctic soil's microbial community demonstrated strong signals of N-limitation, with N-addition increasing all aspects of decomposition tested, including extracellular enzyme activity, the rate-limiting step in decomposition. The corresponding C-addition experiment did not similarly influence the microbial activity of the tundra soil. These results suggest that tundra SOC decomposition is at least seasonally constrained by N-availability through microbial N-limitation. Therefore, explicitly including N as a regulator of microbial growth in this N-poor system is critical to accurately modeling the effects of climatic warming on Arctic SOC decomposition rates. (C) 2012 Elsevier Ltd. All rights reserved.

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