Rapid Cycling of Organic Nitrogen in Taiga Forest Ecosystems |
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Authors: | K Kielland J W McFarland R W Ruess K Olson |
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Institution: | (1) Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775-0180, USA;(2) Department of Biology and Wildlife, University of Alaska, Fairbanks, Alaska 99775-0180, USA |
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Abstract: | ABSTRACT
We examined the dynamics of organic nitrogen (N) turnover in situ across a primary successional sequence in interior Alaska,
USA, in an attempt to understand the magnitude of these fluxes in cold, seasonally frozen soils. Through a combination of
soil extraction procedures and measurements of 13C-enriched CO2 efflux from soils amended in the field with 13C-labeled amino acids, we were able to trace the fate of this N form. Amino acid turnover in situ at soil temperatures of
10°C or below show that amino acids represent a highly dynamic soil N pool with turnover times of approximately 3–6 h. The
rapid turnover of free amino acids is associated with high soil proteolytic activity, which in turn is tightly correlated
with soil protein concentration. Moreover, these estimates of soil amino acid turnover in the field correspond well with measurements
of amino acid turnover under equivalent temperatures in the laboratory. The gross flux of amino acid-N over the growing season
greatly exceeded the annual vegetation N requirement, suggesting that microbial biomass represent a significant sink for this
organic N. Depending on the strength of this sink, N flow via free soil amino acids can potentially account for the entire
N demand of vegetation in the absence of net N mineralization. These relationships underscore the important biogeochemical
role of labile DON fractions in high-latitude forest ecosystems. |
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Keywords: | amino acid boreal forests DON nitrogen cycling protease activity soil processes taiga ecosystems |
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