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.