OOS 12 - What's New Under the Sun? Photodegradation and Novel Drivers of Decompostion in Dryland Ecosystems

Tuesday, August 4, 2009: 8:00 AM-11:30 AM
Galisteo, Albuquerque Convention Center
E. Carol Adair, University of Vermont
Jennifer Y. King, University of California, Santa Barbara; and Leslie Brandt, USDA Forest Service
W. J. Parton, Colorado State University
Litter decomposition contributes to one of the largest fluxes of carbon (C) in the terrestrial biosphere and is a primary control on nutrient cycling. A wealth of research identifies climate (e.g., temperature and precipitation) and litter chemistry (e.g., initial lignin and nitrogen content) as the primary drivers of this microbial process. However, these traditional drivers of biotic decomposition do not accurately describe and predict patterns of decomposition in semi-arid and arid ecosystems, suggesting a role for novel drivers of decomposition in dryland ecosystems. As arid and semi-arid ecosystems make up nearly 40% of the terrestrial land surface, determining what controls decomposition these ecosystems is crucial for predicting how C fluxes will respond to human-induced climate change. Currently, the primary candidate for explaining atypical patterns of decomposition in these ecosystems is photodegradation, the abiotic decomposition of plant litter by solar radiation. Recent research indicates that photodegradation accounts for 5 – 60% of litter mass loss from arid and semi-arid ecosystems. However, our current understanding of this potentially important process is rudimentary. For example, although research indicates that photodegradation contributes substantially to litter mass loss in hot and dry environments but not in humid environments, our understanding of how litter moisture and temperature influence photodegradation is largely qualitative. Additionally, it was initially thought that only ultraviolet-B (UV-B) wavelengths (280-320 nm) drove photodegradation, but recent research has revealed that other wavelengths may be involved as well (UV-A and shortwave photosynthetically active radiation). This incomplete understanding of the abiotic controls on photodegradation, combined with contradictory results regarding the role of litter chemistry and a limited understanding of the indirect effects of solar radiation on decomposition (e.g., UV-induced damage to soil microbes and plant tissue quality), continue to hamper predictive modeling efforts. Furthermore, recent investigations into dryland decomposition have revealed that other processes, such as soil transport and deposition and the structure of the soil food web, may have dramatic impacts on decomposition in these ecosystems. The goals of this session are to present, synthesize, and reconcile results of intensive research on novel drivers of dryland decomposition over the past five years, with an eye towards identifying the next crucial steps for estimating and predicting dryland decomposition in a changing climate.
8:00 AM
 Counteracting effects of ultraviolet-B radiation on litter decomposition
William K. Smith, University of Montana; Wei Gao, Colorado State University; Heidi Steltzer, Fort Lewis College; Matthew D. Wallenstein, Colorado State University; Roger Tree, Colorado State University
8:20 AM
 Photodegradation in species from temperate South America: Direct effects of solar radiation on litter decomposition in terrestrial ecosystems
Amy T. Austin, University of Buenos Aires, IFEVA-CONICET; M. Laura Martínez, University of Buenos Aires and IFEVA-CONICET; Patricia I. Araujo, University of Buenos Aires, IFEVA-CONICET; Andrés A. Grasso, University of Buenos Aires and IFEVA-CONICET; Carlos L. Ballaré, University of Buenos Aires, IFEVA-CONICET
8:40 AM
 The disappearance of surface litter in dryland ecosystems: roles for soil macrofauna and photodegradation
Jayne Belnap, U.S. Geological Survey; Susan L. Phillips, USGS; Stephen Ogle, Colorado State University
9:00 AM
 Photooxidation vs. Enzymatic oxidation: The fate of organic matter in arid soils
Robert Sinsabaugh, University of New Mexico; Marcy E. Gallo, University of New Mexico; Andrea Porras-Alfaro, Western Illinois University; Christian L. Lauber, University of Colorado; Martina Stursova, University of New Mexico
9:20 AM
 Modeling decomposition and photodegradation in dryland ecosystems
E. Carol Adair, University of Vermont; W. J. Parton, Colorado State University; Jennifer Y. King, University of California, Santa Barbara; Leslie Brandt, USDA Forest Service
9:40 AM
9:50 AM
 Effectiveness of different wavebands of solar radiation on litter decomposition in the Sonoran Desert
Thomas A. Day, Arizona State University; Christopher T. Ruhland, Minnesota State University
10:10 AM
 The role of photodegradation in litter decomposition patterns in grassland ecosystems: Results from a 2-year multi-site field experiment
Leslie Brandt, USDA Forest Service; Jennifer Y. King, University of California, Santa Barbara; Sarah E. Hobbie, University of Minnesota; Daniel G. Milchunas, Colorado State University; Robert Sinsabaugh, University of New Mexico
10:30 AM
 Addressing the dryland decomposition conundrum by integrating vegetation structure, soil transport, and ultraviolet (UV) photodegradation
Heather L. Throop, New Mexico State University; Steven R. Archer, University of Arizona; Paul W. Barnes, Loyola University
10:50 AM
 Grazer and exotic plant species modifications of bacterial populations and organic matter processing in Yellowstone National Park winter range grasslands
E. William Hamilton III, Washington and Lee University; C. Eric Hellquist, SUNY-Oswego; Bonnie Fay, Washington and Lee University; Woodrow Friend, Washington and Lee University; Briana Gregory, Washington and Lee University; Kim Wahl, SUNY-Oswego
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