PARENT SESSION
Oral Session # 8: Plant Ecology I: Physiology and Function I.
Presiding: E Hamerlynck
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.
The impact of elevated CO2, nitrogen and biodiversity on tissue quality and litter decomposition.
Knops, Johannes*,1, Naeem, Shahid2, 1 School of Biological Sciences, Lincoln, NE, US2 Zoology Department, Seattle, WA, US
ABSTRACT- Increasing atmospheric CO2 concentrations, declining biodiversity and increased nitrogen deposition are changing productivity in many ecosystems. These global changes also impact plant and litter quality and have the potential to alter ecosystem nitrogen cycling. We examined nitrogen cycling changes induced by changes in plant tissue quality and decomposition using a three factorial experiment with elevated CO2 (ambient, 368 vs. elevated, 560 mol mol-1), nitrogen fertilization (unamended vs. deposition of 4 g N m-2 yr-1), and species richness (1, 4, 9 or 16 species). We measured aboveground plant tissue and litter quality, e.g. carbon and nitrogen, soluble, hemicellulose, cellulose and lignin fractions. In addition, we measured aboveground litter decomposition over one and two year periods with in-situ litterbags. Elevated CO2 decreased nitrogen concentrations by 9%. Elevated nitrogen increased nitrogen concentrations by 7% while decreasing lignin concentrations by 16%. However, species richness had a much larger impact than either CO2 or nitrogen fertilization, with higher species richness decreasing tissue nitrogen concentrations by 18%, increasing cellulose by 20% and decreasing lignin concentrations by 16%. However, in contrast we found only minimal differences in litter decomposition across the treatments. Thus changes in tissue quality caused by elevated CO2, nitrogen fertilization and changes in plant species richness do not result in marked changes in litter decomposition rates or nitrogen released during litter decomposition. The plant tissue quality response supports the hypothesis that plant communities produce different quality of biomass and litter when resource availability or competition for nitrogen changes. However, these tissue quality changes have only a minor impact on litter decomposition and nitrogen cycling. Consequently, litter decomposition acts as a negative feedback. Short term elevated CO2, nitrogen fertilization and changes in species richness lead to changes in productivity and tissue quality. However, decomposition rates do not reflect these quality changes. Thus, long-term the accumulation of limiting nutrients in litter will lead to a negative feedback on productivity, diminishing the impact of changes in biotic and abiotic changes on productivity.
Key words: decomposition, nitrogen cycling, elevated CO2, tissue quality