HR: 0800h
AN: B41A-0091    [Abstracts]
TI: CO$_{2}$, Temperature, and Soil Moisture Interactions Affect NDVI and Reproductive Phenology in Old-Field Plant Communities
AU: * Engel, C
EM: cayenne@utk.edu
AF: University of Tennessee, Knoxville, 569 Dabney Hall, Knoxville, TN 37996-1610
AU: Weltzin, J
EM: jweltzin@utk.edu
AF: University of Tennessee, Knoxville, 569 Dabney Hall, Knoxville, TN 37996-1610
AU: Norby, R
EM: norbyrj@ornl.gov
AF: Oak Ridge National Lab, One Bethel Valley Road Bldg. 1062, Oak Ridge, TN 37831-6422
AB: Plant community composition and ecosystem function may be altered by global atmospheric and climate change, including increased atmospheric [CO$_{2}$], temperature, and varying precipitation regimes. We are conducting an experiment at Oak Ridge National Laboratory (ORNL) utilizing open-top chambers to administer experimental treatments of elevated CO$_{2}$ (+300 ppm), warming (+ 3 degrees Celsius), and varying soil moisture availability to experimental plant communities constructed of seven common old-field species, including C$_{3}$ and C$_{4}$ grasses, forbs, and legumes. During 2004 we monitored plant community phenology (NDVI) and plant reproductive phenology. Early in the year, NDVI was greater in wet treatment plots, and was unaffected by main effects of temperature or CO$_{2}$. This result suggests that early in the season warming is insufficient to affect early canopy development. Differences in soil moisture sustained throughout the winter and into early spring may constitute an important control on early canopy greenup. Elevated CO$_{2}$ alleviated detrimental effects of warming on NDVI, but only early in the season. As ambient temperatures increased, elevated temperatures negatively impacted NDVI only in the dry plots. Wetter conditions ameliorate the effects of warming on canopy greenness during the warmer seasons of the year. Warming increased rates of bolting, number of inflorescences, and time to reproductive maturity for {\it Andropogon virginicus} (a C$_{4}$ bunchgrass). {\it Solidago Canadensis} (a C$_{3}$ late-season forb) also produced flowers earlier in elevated temperatures. Conversely, none of the C$_{3}$ grasses and forbs that bolt or flower in late spring or early summer responded to temperature or CO$_{2}$. Results indicate that warming and drought may impact plant community phenology, and plant species reproductive phenology. Clearly community phenology is driven by complex interactions among temperature, water, and CO$_{2}$ that change throughout the season. Our data stresses the importance of multifactor experiments examining global change, given that often plants respond to interactions of multiple factors rather than solely main effects.
DE: 1851 Plant ecology
DE: 1854 Precipitation (3354)
DE: 1600 GLOBAL CHANGE (New category)
DE: 1610 Atmosphere (0315, 0325)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting