Monday, August 6, 2007 - 3:20 PMCOS 13-6: Exploring a plant-soil-mycorrhiza feedback with Rhododendron maximum in a temperate hardwood forest
Nina Wurzburger and Ronald L Hendrick. University of Georgia
Ericaceous plant litter polyphenols influence the N cycle of terrestrial ecosystems through the formation of recalcitrant protein-tannin complexes. The accumulation of protein-tannin N in soils along with the ability of the ericoid mycorrhizal fungi of ericaceous plants to access protein-tannin N is a hypothesized plant-soil-mycorrhiza feedback. We examined this hypothesis in southern Appalachian forest microsites with and without the understory shrub Rhododendron maximum. Forest microsites with R. maximum have greater standing stocks of soil N and lower soil N availability compared to forest microsites without the shrub. We examined the soil fate of reciprocally placed 15N enriched protein-tannin complexes. Based upon recovery of 15N in soil N pools, microbial biomass and roots, protein-tannin complexes derived from R. maximum leaf litter were more recalcitrant than those derived from hardwood leaf litter. Ericoid mycorrhizal roots of R. maximum were more enriched in 15N compared to arbuscular and ectomycorrhizal roots of forest trees, particularly with R. maximum derived complexes. These results suggest that the N contained in recalcitrant R. maximum protein-tannin complexes are more available to R. maximum compared to forest trees. Mechanisms by which R. maximum ericoid mycorrhizal roots acquire protein-tannin N may include extracellular enzyme production by root fungi. This root fungal community is diverse and includes ericoid symbionts, ectomycorrhizal symbionts, saprotrophs and several unknown fungi. A plant-soil-mycorrhizal feedback, combined with an N conserving habit, may contribute to both the expansion of R. maximum and the concomitant suppression of other plant species in southern Appalachian forests.