Nutrient release from decomposing litter in Rocky Mountain coniferous forests: influence of nutrient availability

We examined patterns of N and P uptake and release from a wide variety of litter types, including leaves, needles, moss, roots, and wood, for 4 years in three forests (lodgepole pine (Pinuscontorta Loud.), white spruce (Piceaglauca (Moench) Voss)–lodgepole pine, and Engelmann spruce (Piceaengelmannii Parry ex Engelm.)–subalpine fir (Abieslasiocarpa (Hook.) Nutt.)) and a small clearcut, in the Rocky Mountains of Alberta. Decomposition was more rapid and N release began sooner in the clearcut than in the forests, but N release began at the same stage of decomposition at all sites. In most litter types, a period of net immobilization of N was followed by a period of net release; only litter types particularly rich in N had an initial leaching phase. Each litter type initially gained or lost N depending on its original concentration, such that N contents converged after 1 or 2 years. The N content at convergence differed among litter types. Phosphorus was usually released immediately. The rate of P loss also varied according to the initial P concentration, and the P contents of all litter types converged within 1 year. The availability of N and P in the forest floor did not affect the rate of N and P release from a standard substrate placed at all sites. The concentrations of N and P in the litter influenced the rate of uptake of N or P during the first 1–3 years, but was not consistently related to nutrient availability in the forest floors at the four sites.