HR: 1340h
AN: B43B-1170    [Abstracts]
TI: Rainfall, nitrogen deposition and fire disturbance impacts in a California coastal grassland
AU: * Potts, D L
EM: pottsdl@buffalostate.edu
AF: Buffalo State College, 1300 Elmwood Ave., Buffalo, NY 14222,
AU: Winston, G
EM: gwinston@uci.edu
AF: University of California - Irvine, 321 Steinhaus Hall, Irvine, CA 92697,
AU: Rocha, A
EM: arocha@uci.edu
AF: University of California - Irvine, 321 Steinhaus Hall, Irvine, CA 92697,
AU: Suding, K N
EM: ksuding@uci.edu
AF: University of California - Irvine, 321 Steinhaus Hall, Irvine, CA 92697,
AU: Goulden, M L
EM: mgoulden@uci.edu
AF: University of California - Irvine, 321 Steinhaus Hall, Irvine, CA 92697,
AB: In semi-arid ecosystems, shifts in soil moisture availability may mediate the response of individual species, communities and ecosystems to disturbance or changes in nutrient availability. How these interactive effects scale through different levels of ecological organization is poorly understood but essential for robust predictions of the effects of environmental change. In 2007, a year of record low rainfall, we conducted a prescribed fire in a coastal grassland in Orange County California. Within both burned and unburned portions of the grassland, we increased and decreased rainfall (with water addition and rainout shelters, respectively) and increased nitrogen (with N fertilization) in all possible treatment combinations. We asked the question: can physiological responses of the dominant species predict changes in ecosystem function to these interactive environmental manipulations? The native perennial bunchgrass, Nassella pulchra had higher rates of CO ₂ uptake and stomatal conductance than the nonnative annual grass, Bromus diandrus across rainfall treatments in both the burned and unburned areas. Both species maintained relatively constant physiological responses regardless of environmental manipulation. Thus, based on these resilient individual-level responses, we predicted that ecosystem-responses would be relatively resilient to the environmental changes. Consistent with this prediction, burning and nitrogen did not strongly affect ecosystem function. However, we detected relatively large responses at the ecosystem level in response to rainfall manipulations, and these effects were generally consistent across burning and N fertilization treatments. Ecosystem respiration, photosynthesis (GEE) and evapotranspiration (ET) declined in response to rainfall removal but did not respond to increases in rainfall. In contrast, the response of annual net primary productivity (ANPP) and a canopy spectral index (NDVI) was greatest in rainfall addition plots. NDVI was correlated with ANPP, GEE and ET in both experiments. During this extremely dry growing season, many on the ecosystem responses were likely driven by soil microbial and plant population- level changes rather than changes in individual plant physiology. Ongoing research at the site will determine whether these relationships will change with annual climatic variation and as longer-term processes (e.g., species turnover, organic matter) begin to contribute more to individual and ecosystem responses.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0469 Nitrogen cycling
DE: 1630 Impacts of global change (1225)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting