Abstract: Aims The direct effects of atmospheric and climatic change factors—atmospheric [CO₂], air temperature and changes in precipitation—can shape plant community composition and alter ecosystem function. It is essential to understand how these factors interact to make better predictions about how ecosystems may respond to change. We investigated the direct and interactive effects of [CO₂], warming and altered soil moisture in open-top chambers (OTCs) enclosing a constructed old-field community to test how these factors shape plant communities.
Materials and Methods The experimental facility in Oak Ridge, TN, USA, made use of 4-m diameter OTCs and rain shelters to manipulate [CO₂] (ambient, ambient + 300 ppm), air temperature (ambient, ambient + 3.5°C) and soil moisture (wet, dry). The plant communities within the chambers comprised seven common old-field species, including grasses, forbs and legumes. We tracked foliar cover for each species and calculated community richness, evenness and diversity from 2003 to 2005.
Important findings This work resulted in three main findings: (1) warming had species-specific effects on foliar cover that varied through time and were altered by soil moisture treatments; (2) [CO₂] had little effect on individual species or the community; (3) diversity, evenness and richness were influenced most by soil moisture, primarily reflecting the response of one dominant species. We conclude that individualistic species responses to atmospheric and climatic change can alter community composition and that plant populations and communities should be considered as part of analyses of terrestrial ecosystem response to climate change. However, prediction of plant community responses may be difficult given interactions between factors and changes in response through time.

Key words: climate change, foliar cover, multi-factor interactions, diversity, richness