Direct and indirect control by snow cover over decomposition in alpine tundra along a snowmelt gradient
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We assessed direct and indirect effects of snow cover on litter decomposition and litter nitrogen release in alpine tundra. Direct effects are driven by the direct influence of snow cover on edaphoclimatic conditions, whereas indirect effects result from the filtering effect of snow cover on species’ abundance and traits. We compared the in situ decomposition of leaf litter from four dominant plant species (two graminoids, two shrubs) at early and late snowmelt locations using a two-year litter-bag experiment. A seasonal experiment was also performed to estimate the relative importance of winter and summer decomposition. We found that growth form (graminoids vs. shrubs) are the main determinants of decomposition rate. Direct effect of snow cover exerted only a secondary influence. Whatever the species, early snowmelt locations showed consistently reduced decomposition rates and delayed final stages of N mineralization. This lower decomposition rate was associated with freezing soil temperatures during winter. The results suggest that a reduced snow cover may have a weak and immediate direct effect on litter decomposition rates and N availability in alpine tundra. A much larger impact on nutrient cycling is likely to be mediated by longer term changes in the relative abundance of lignin-rich dwarf shrubs.
KeywordsGrowth form Nitrogen mineralization Snow cover Litter decomposition Alpine tundra
We are grateful to Serge Aubert and to Céline Flahaut, Geneviève Girard, Cécile Bayle, Marie-Pascale Colace and Mathieu Chausson for their help in the field and in the laboratory. We gratefully thank Natalia Pérez Harguindeguy, Fabien Quétier, Matthew Robson, Mason Campbell and two anonymous reviewers for their helpful comments on an earlier version of this manuscript. Logistical support was provided by the Station Alpine Joseph Fourier, the alpine field station of the University Joseph Fourier. The work was funded by the ANR-06-BLAN-0301 “Microalpes” project.
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