Analysis of litter decomposition in an alpine tundra

Decomposition of plant litter regulates nutrient cycling and transfers of f ixed carbon to soil organic matter pools in terrestrial ecosystems. Climate , as well as factors of intrinsic Litter chemistry, often govern the rate o f decomposition and thus the dynamics of these processes. Initial concentra tions of nitrogen and recalcitrant carbon compounds in plant litter are goo d predictors of litter decomposition rates in many systems. The effect of e xogenous nitrogen availability on decay rates, however, is not well defined . Microclimate factors vary widely within alpine tundra sites, potentially affecting litter decay rates at the local scale. A controlled factorial exp eriment was performed to assess the influence of landscape position and exo genous nitrogen additions on decomposition of surface foliage and buried ro ot litter in an alpine tundra in the Front Range of the Rocky Mountains in Colorado, U.S.A. Litter bags were placed in three communities representing a gradient of soil moisture and temperature. Ammonium nitrate was applied o nce every 30 days at a rate of 20 g N.m(-2) during the 3-month growing seas on. Data, as part of the Long-Term Inter-site Decomposition Experiment Team project, were analyzed to ascertain the effects of intrinsic nitrogen and carbon fraction chemistry on litter decay in alpine systems. Soil moisture was found to be the primary controlling factor in surface litter mass loss. Root litter did not show significant mass loss following first growing sea son. Nitrogen additions had no effect on nitrogen retention, or decompositi on, of surface or buried root litter compared with controls. The acid-insol uble carbon fraction was a good predictor of mass loss in surface litters, showing a strong negative correlation. Curiously, N concentration appeared to retard root decomposition, although degrees of freedom limit the confide nce of this observation. Given the slow rate of decay and N loss from root Litter, root biomass appears to be a long-term reservoir for C and N in the alpine tundra.