PARENT SESSION
Contributed Oral Session 33: Grassland and Shrubland Communities
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal

Species-specific and community responses of an old-field plant community to the interacting factors of elevated [CO₂], warming, and soil moisture content.

Engel, Cayenne^*,1, Weltzin, Jake ¹, Norby, Rich ², ¹ University of Tennessee - Knoxville, Knoxville, TN, USA² Oak Ridge National Laboratory, Oak Ridge, TN, USA

ABSTRACT- Plant community composition and ecosystem function may be altered by global atmospheric and climate change, particularly atmospheric [CO₂], temperature, and precipitation. A multi-factor experiment at Oak Ridge National Laboratory utilizes open-top chambers to administer treatments of elevated CO₂ (+300 ppm) and elevated temperature (+ 3 degrees C) in a split plot water treatment design. Plant communities constructed of seven common old-field species, including grasses, forbs, and legumes were constructed in 2002. We monitored foliar cover, morphology, density and reproductive phenology of each plant species during 2003 and 2004. After two years of experimental treatments, water availability was the most important resource influencing species-specific and community development. Diversity and evenness and richness were at least 10% lower in wet plots, where total foliar cover and dominance was greater. The only community dominant that responded consistently to the experimental treatments was Dactylis glomerata (C₃ bunchgrass), wherein foliar cover of Dactylis was at least 30% lower in dry plots and at least 40% lower in warmed plots during the second year. In addition, cover of Dactylis was four times greater in the ambient temperature treatment within wet plots than in all other treatment combinations late in the growing season of 2004 (temperature x water interaction; P < 0.02). Subdominant species (less than 10% mean foliar cover) such as Andropogon virginicus or Solidago canadensis often had greater foliar cover in dry, or warming treatments, probably due to a release from competitive exclusion by dominant species. Additionally, warming did facilitate earlier flowering in Andropogon (by 29 days) and Solidago (by 21 days), which typically develop later in the season (P < 0.02). Interestingly, species that flower in spring and early summer did not respond to warming in terms of flowering dates and development.

Key words: climate change, warming, reproductive phenology, diversity