NUTRIENT RELEASE FROM DECOMPOSING LITTER IN ROCKY-MOUNTAIN CONIFEROUSFORESTS - 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, fo r 4 years in three forests (lodgepole pine (Pinus contorta Loud.), whi te spruce (Picea glauca (Moench) Voss) - lodgepole pine, and Engelmann spruce (Picea engelmannii Parry ex Engelm.) - subalpine fir (Abies la siocarpa (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 sta ge of decomposition at all sites. In most litter types, a period of ne t immobilization of N was followed by a period of net release; only li tter types particularly rich in N had an initial leaching phase. Each litter type initially gained or lost N depending on its original conce ntration, such that N contents converged after 1 or 2 years. The N con tent at convergence differed among litter types. Phosphorus was usuall y released immediately. The rate of P loss also varied according to th e initial P concentration, and the P contents of all litter types conv erged within 1 year. The availability of N and P in the forest floor d id not affect the rate of N and P release from a standard substrate pl aced at all sites. The concentrations of N and P in the litter influen ced the rate of uptake of N or P during the first 1-3 years, but was n ot consistently related to nutrient availability in the forest floors at the four sites.