Abstract, Ecological Society of America Annual Meeting, Madison, WI, August, 2001.

WELTZIN, J.F.¹, R.J. NORBY², AND L.M. THOMAS¹. ¹University of Tennessee, Knoxville, TN 37996 and ²Oak Ridge National Laboratory, Oak Ridge, TN 37831. Production of invasive plants in response to elevated CO₂ in a closed-canopy, deciduous forest..

Increases in the concentration of carbon dioxide ([CO₂]) in the atmosphere, and invasions by non-native organisms, are both predicted to change plant communities and ecosystems in the near future. Because interactions between these two variables may be greater than their individual effects, we are investigating the response of non-native, invasive plants to elevated [CO₂] in an ongoing, free-air CO₂ enrichment (FACE) facility on the Oak Ridge National Environmental Research Park, Tennessee. Five 25-m diameter plots within a stand of sweetgum (Liquidambar styraciflua) have received either ambient (= control) or elevated (537 ppm) [CO₂] since 1998. In Fall 2000, we clipped subplots within each plot to determine biomass of non-native, invasive woody plants (Lonicera japonica, Ligustrum sinense), an invasive, annual C₄ grass (Microstegium vimineum), and other taxa. Total understory biomass did not differ between ambient and elevated treatments (194 g/m²; P = 0.25). Similarly, biomass of invasive woody plants did not differ (140 g/m2; P = 0.39). However, production of M. vimineum was greater in ambient (82 g/m²) than elevated (58 g/m²) treatments. Total, woody, and M. vimineum biomass were not correlated with mean soil temperature (at 10 cm) or mean soil water content (top 20 cm) in 2000. Results suggest that factors other than direct or even indirect effects of CO₂ enrichment, such as disturbance or light availability, may dictate at least the proximal response of invasive plants to increasing atmospheric [CO₂].