Litter Decomposition and Nitrogen Dynamics in Aspen Forest and Mixed-Grass Prairie

Temperature and moisture have larger effects on litter decomposition than litter quality on regional scales. We tested whether this also holds for microclimatic differences between adjacent habitats. We placed litter of aspen (Populus tremuloides) and prairie grasses in both forest and prairie. Microclimate was varied by shading half the litter in both habitats. Litter was set out in May and retrieved after 4, 9, 16, and 21 wk. Decomposition rates averaged across sites and treatments were significantly lower for aspen (k = 0.44 yr−1) than grass litter (1.36 yr−1), reflecting differences in nitrogen (N) content between litter types (aspen, 0.62%; grass, 1.07%). Decomposition rates were highest in unshaded prairie, suggesting that shade may limit decomposition in forests. N mineralized from the litter was collected by ion-exchange resins placed under the litter, while uncovered resins collected mineral N deposited from the atmosphere. Less mineral N was collected by resins under litter than by uncovered resins, suggesting that litter accumulated mineral N deposited from the atmosphere. The N accumulation rates were significantly higher in aspen than grass litter, in accordance with a lower N concentration in aspen litter. Thus, on a local scale, decomposition rates and N dynamics were more strongly affected by litter quality than by shading or habitat.