Document: MIC-3-59-64

Decomposition and nutrient cycling in a changing environment: Is genetic diversity redundant to ecosystem function?

MADRITCH, M.D.* and M.D.HUNTER

University of Georgia, Athens, GA 30602 USA ¹

Abstract:
Anthropogenic forces are concurrently altering global carbon and nitrogen cycles while reducing biological diversity. Our study addresses how a loss of intraspecies genetic diversity affects the fluxes of carbon (C) and nitrogen (N) in an ecosystem. Leaf secondary metabolites participate in the control of decomposition, along with environmental factors such as temperature and moisture. Recent work has shown that these secondary compounds vary within species according to genotype and environment. We are studying the relative effects of genetic diversity of Quercus laevis leaf litter and environmental factors on decomposition. Using previously genotyped individuals, we have collected specific genotypes of leaves and established a three-year litter bag decomposition study with treatments varying in intraspecific litter diversity. Initial litter chemistry of randomly chosen genotypes showed partial genetic control of condensed tannins and C:N ratios. After 6 months of decomposition, there was a significant effect of genotype on litter N retention and net C movement. Immobilization of C and N in the litter differed among genotypes, while overall decomposition remained low. For both C and N, there was no apparent universal effect of decreased genotypic diversity; single genotype litters did not invoke similar C and N responses compared to a mixed litter treatment. However, there were large and significant variations in C and N fluxes among litter genotypes, indicating that litter genotype affects C and N cycling through secondary chemistry. In all cases, mixed litter treatment response was never an average of the other individual genotype treatment responses. This is preliminary evidence that reductions in intraspecific genetic diversity have ecosystem level affects that are not predictable by average litter quality indices. Whether or not the redundancy of soil biota can compensate for the lack of redundancy in intraspecific litter diversity remains to be seen.

Keywords: ecosystem function, genetic diversity, nitrogen, nutrient cycling, decomposition

This abstract is being presented at: 10:30 AM in session:
Poster Session #13: Decomposition and Soil Respiration.