HR: 0800h
AN: B41C-0641    [Abstracts]
TI: Quantifying carbon dioxide fluxes from photodegrading plant litter in arid ecosystems
AU: * Brandt, L A
EM: brand142@umn.edu
AF: University of Minnesota Department of Ecology, Evolution and Behavior, 100 Ecology Building 1987 Upper Buford Circle, Saint Paul, MN 55108, United States
AU: Bohnet, C
EM: cmohni@uni.edu
AF: University of Northern Iowa Department of Biology, 144 McCollum Science Hall, Cedar Falls, IA 50614, United States
AU: King, J Y
EM: jyking@umn.edu
AF: University of Minnesota Department of Soil, Water, and Climate, 439 Borlaug Hall 1991 Upper Buford Circle, Saint Paul, MN 55108, United States
AB: Biogeochemical models fail to fully explain patterns of litter decomposition in arid ecosystems. Previous research in arid ecosystems has demonstrated that photodegradation, the break-down of chemical compounds by solar radiation, can account for a significant proportion of surface litter mass loss in these ecosystems. However, little is known about the mechanisms of this mass loss. We investigated the potential for solar radiation to lead to direct mineralization to carbon dioxide (CO₂) in 5 litter species native to both arid and mesic ecosystems that receive high levels of solar radiation. In one experiment, we exposed litter to a factorial design of ultraviolet (UV) radiation (UV+, UV-), and sterilization (sterile, non-sterile) over a 10 week period in the lab under dry conditions. Over the ten week period, the only significant effect on CO₂ emissions was due to UV exposure, with UV+ treatments producing 6 times the amount of CO₂ produced under the UV- treatments. CO₂ production rates remained constant over the 10 week period, following a zero order decay model. In a second experiment, we exposed litter of one species to natural solar radiation outdoors on clear, sunny days close to the summer solstice in Minnesota. Our emission rates were seven times higher under natural radiation than under lamps in the lab, possibly due to increased temperature and higher radiation intensity. We found that UV radiation accounted for the largest proportion (47%) of photochemically-induced CO₂ emissions, while shortwave visible radiation (<500 nm) accounted for 38% of CO₂ emissions. A small percentage (15%) was due to wavelengths longer than 500 nm. Production of CO₂ under natural radiation averaged 13 mg C m^-2 d^-1 on clear sunny days. Assuming a linear relationship between total solar irradiance and CO₂ production, we estimate that CO₂ production via photodegradation is between 3.5 and 7 g C m^-2 y^{- 1} in arid ecosystems in the southwestern USA. Taken together with low levels of litter production, our estimates suggest that photochemical mineralization to CO₂ could account for as much as 20% of annual litter mass loss in arid ecosystems. Therefore, abiotic CO₂ production through photodegradation may be a major process by which carbon is lost from plant litter.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting