Decompostion of Roots and Leaves in a Nothern Temperate Forest.

Short-term litter decomposition studies have provided important insight into regulation of ecosystem C cycling, and have increased our understanding of C transfers from vegetation to soil.  Previous work has shown that the relative importance of leaf and root litter inputs to soil C pools can vary substantially across and within temperate forests.  Despite the importance of different organic matter sources contributing to soil C, we do not have good comparative studies of direct decomposition of leaf land root litter, nor of differences in the chemistry of these different organic matter sources.  We examined nitrogen controls on leaf and root decomposition and to assess the relative importance of these litter input sources to long-term soil organic matter in an aspen-maple-oak forest developing on glacial outwash sands at the University of Michigan Biological Station.  We placed 105 mixed root litter bags and 267 single (big tooth aspen, red oak, white pine, red maple) and mixed leaf litter bags at the site to follow long-term litter decomposition.  Our first year results show that roots lost an average of 26.8% of the initial mass, compared to a mass loss of 50.2% for the mixed species litter bags.  Single species litter lost from 36.7% (aspen) to 48.2% (red maple) during the first year.  Using k-values for the individual species, we estimated the expected decomposition of mixed leaf litter bags, and found that actual litter loss was approximately 30% greater than expected values.  Fine roots had a lower nitrogen concentration and higher CN ratio than the mixed leaf litter assemblages.  Generally, higher decomposition was related to higher initial nitrogen concentrations and lower CN ratios.   These results suggest different forest litter sources will contribute differently to long-term soil carbon pools, and that successional or human-induced changes in forest composition will alter rates of soil C storage.