Rhododendron thickets alter N cycling and soil extracellular enzyme activities in southern . Appalachian hardwood , forests

m ~ m w . regeneration and alters forest community structure in southern Appalachian p=A, hardwood forests. Using paired plots and reciprocal litter transplants in forests Polyphenol oxidase; with and without R. maximum cover, we examined the influence of R. maximum on Protease; Leaf litter litter mass and quality, N cycling and soil extracellular enzymes. Standing stocks of soil organic matter, soil N, leaf litter mass and fine root biomass were greater in forest; with R. maximum than those without. Tannin extracts from R. maximum foliage, and leaf litter and fine roots collected under R. maximum had a relatively high capacity to precipitate protein compared to extracts from trees. Across the growing season, soil inorganic N availability was generally lower under R. maximum, mostly due to reduced NO3 availability. Our data suggest that R. maximum litter alters N cycling through the formation of recalcitrant polyphenol-organic N complexes. Soil extracellular enzymes indicate the potential processing rates of organic substrates. Between forest types, polyphenol oxidase activity was greatest in R. maximum 0 horizons, regardless of litter type, suggesting that the local microbial community can better degrade and access protein-tannin-complexed N. Protease activity did not differ between forest types, but was greater on R. maximum leaf litter than hardwood leaf litter. The alteration of the N cycle via the formation of polyphenot-oqanic N complexes may contribute to hardwood seedling suppression, while the enzymatic release of these complexes by ericoid mycorrhizal fungi may increase N acquisition for R. maximum and contribute to its expansion in southern Appalachian forests. Q 2006 Elsevier GmbH. All rights reserved.