Fraley, Philip , Ruhland, Christopher .
The effects of leaf optics on photodegradation of Artemisia tridentata litter sampled along an elevational gradient.
A major contributor to the global carbon cycle is the decomposition of plant litter. Carbon dioxide released from decomposing organic material is an order of magnitude greater than that of fossil fuel combustion. Decomposition rates are typically dependent on climatic factors such as temperature and moisture as well as initial litter chemistry. However, the relative contribution of different wavelengths of radiation has only recently been examined and is not completely understood, especially in arid systems. The process of photodegradation involves the direct and indirect breakdown of plant litter components. Lignin, a major constituent of the secondary cell wall, has been implicated as a target for photodegradation. Lignin strongly absorbs ultraviolet radiation (“UV;” 280-400nm) and it is unknown if initial concentrations influence photodegradation of plant litter. We collected leaves of Artemisia tridentata ssp. wyomingensis (Wyoming Big Sagebrush) from a 1000-m altitudinal gradient in the Bighorn Mountains in Wyoming. Epidermal transmittance of UV decreased from 20 to 12% along this gradient and there was a concomitant increase in concentrations of bulk-soluble UV-absorbing compounds. We hypothesized that litter from high elevations should photodegrade slower than their lower elevation counterparts due to increased UV-screening by these compounds. In addition, we measured initial concentrations of lignin, cellulose and hemicellulose of these leaves to provide an explanation for mass-loss rates. Litter was then placed under lamps and exposed to 3.2 kJ m-2 d-1 of UV in a laboratory setting. We examined decomposition rates at 49, 183 and 310 days. Mass loss was negatively correlated with elevation on all sampling dates and this relationship became more apparent over time. It appears that UV levels should be taken into consideration when trying to model decomposition rates in arid climates.
1 - Minnesota State University , Biological Sciences, TS 242 Trafton Sciences Center , Mankato , MN, 56001, USA
Presentation Type: Poster
Candidate for Awards:None