Implications of atmospheric CO2 enrichment and climatic change for the geographical distribution of two introduced vines in the U.S.A.

The continuing increase in the atmospheric carbon dioxide concentration resulting from fossil fuel combustion and deforestation may change the ecological impact and geographical distribution of kudzu (Pueraria lobata Ohwi) and Japanese honeysuckle (Lonicera japonica Thunb.) in the U.S.A. Both vines were introduced about a century ago from Japan and have become naturalized weeds. Westward range expansion is currently limited by drought during seedling establishment, while northward range expansion is limited by low temperature sensitivity of overwintering stems.Direct effects of CO₂ enrichment on growth were assessed by growing the plants in controlled environment chambers at 350, 675, or 1000 l/L CO₂. In both species, CO₂ enrichment increased instantaneous water use efficiency by increasing photosynthetic rates and reducing transpiration rates. During a drought stress, CO₂ enrichment delayed significant decline in total water potential of kudzu by several days. When grown in a cool temperature regime of 18/12 °C day/night, the CO₂ enrichment significantly increased leaf area and total biomass of both species and plants were taller and had more branches. These results suggested that atmospheric CO₂ enrichment may allow westward and northward spread of both species in the U.S.A.Indirect effects of CO₂ induced climate change (Greenhouse Effect) on the vines' distribution were assessed. Predictions based on current models of climatic response were used to project changes in winter temperatures at doubled CO₂ concentrations. Increases in average and minimum winter temperatures by 3 °C could allow northward spread of both species by several hundred kilometers. Projected decreases in summer precipitation may minimize westward spread, despite improved water use efficiency and increased drought tolerance.This study was supported by NSF Grant No. BSR82-15533 and Contract No. DEAS05-83ER06177 from the Carbon Dioxide Research Office, Dept. of Energy to B. R. Strain and NSF Grant No. BSR83-14925 for the Duke University Phytotron.