ARCUS | Arctic Research Consortium of the United States

7th Annual ARCUS Award for Arctic Research Excellence

Winner Interdisciplinary Research
Submitted by   Michael Weintraub
Authors   Michael N. Weintraub and J. P. Schimel
Category   Interdisciplinary Research
Title   Interactions Between Carbon and Nitrogen Mineralization and Soil Organic Matter Chemistry in Arctic Tundra Soils
Affiliation   Ecology, Evolution, and Marine Biology (EEMB), University of California, Santa Barbara (UCSB), Santa Barbara, CA, USA

Abstract

We used long term long-term lab incubations and chemical fractionation to characterize the mineralization dynamics of organic soils from tussock, shrub, and wet meadow tundra communities, to determine the relationship between soil organic matter (SOM) decomposition and chemistry, and to quantify the relative proportions of carbon (C) and nitrogen (N) in tundra SOM that are biologically available for decomposition. Despite large losses of soil C, respiration rates generally did not decline, and SOM chemistry was relatively unchanged after the incubation. The decomposition dynamics we observed suggest that tundra SOM, which is largely plant detritus, fits within existing concepts of the litter decay continuum. The lack of changes in organic matter chemistry indicates that this material had already decomposed to the point where the breakdown of labile constituents was tied to lignin decomposition. Our results suggest that a large proportion of tundra SOM is potentially mineralizable, despite the fact that decomposition was dependent on lignin breakdown, and that the historical accumulation of organic matter in tundra soils is the result of field conditions unfavorable to decomposition, and not the result of fundamental chemical limitations to decomposition. Our study also suggests that the anticipated increases in shrub dominance may substantially alter the dynamics of SOM decomposition in the tundra.