Rhododendron thickets alter N Cycling and soul extracellular enzyme activities in southern Appalachian hardwood forests

Abstract

Rhododendron maximum L., a spreading understory shrub, inhibits overstory. Regeneration and alters forest community structure in southern Appalachian hardwood forests. Using paired plots and reciprocal litter transplants in forests with and without R. maximum cover, we examined the influence of R. maximum on 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, 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. activity did not differ between forest types, but was greater on R. maximum than hardwood leaf litter. The alteration of the N cycle via the formation of polyphenot-organic 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.

Citation

Wurzburger, Nina; Hendrick, Ronald L. 2007. Rhododendron thickets alter N Cycling and soul extracellular enzyme activities in southern Appalachian hardwood forests. Pedobiologia, Vol. 50: 563-576