Climate warming in the arctic may shift dominant vegetation from graminoids to deciduous shrubs, whose functional traits could, in turn, alter biotic and abiotic controls over biogeochemical cycling of carbon and nitrogen (N). In arctic tundra near Toolik Lake, Alaska, we used a snow depth manipulation experiment across a natural gradient of shrub abundance and height (Low, Medium and High) to test whether the amount of snow that accumulates around arctic deciduous shrubs alters the microenvironment enough to increase litter decomposition rates. In these sites, we decomposed a common substrate (Betula papyrifera var. neoalaskan) over three years to compare the environmental effects of snow and shrubs on mass and N loss. We also examined litter quality indices for common shrub, graminoid and moss species across this gradient and decomposed these litters in a common garden to determine differences in relative decomposability. Specifically, we hypothesized that; 1) moderate increases in snow will increase litter decomposition rates by providing a more favorable microclimate for decomposition, 2) graminoid and deciduous shrub litter will decompose more quickly than evergreen or moss litter due to lower initial lignin content.
Results/Conclusions
After three years of incubation, the common substrate lost about 50% of its initial mass across all sites, with approximately 30% occurring within the first year. Vegetation type had a significant effect on mass loss; the Low shrub site had the greatest mass loss over the three year incubation period (F=771.9, p=<0.0001) when compared to the other two sites. Estimated k-values ranged from 0.28 yr-1(±0.01), 0.22 yr-1 (±0.01), and 0.25 yr-1 (±0.01) at the Low, Medium, and High shrub sites, respectively and were significantly different across sites (F=18.0, p=<0.0001). Snow addition had no significant affect on mass loss or k-values at any of the three sites. Common garden data is currently being analyzed. Our data suggest that at least at this time scale, a moderate increase in snow does not influence rates of litter decomposition. Based on environmental effects alone, a shift to a shrubbier arctic may actually result in lower rates of litter decomposition than in tussock tundra systems.
