EFFECTS OF CO2 ENRICHMENT ON THE GROWTH AND MORPHOLOGY OF A NATIVE AND AN INTRODUCED HONEYSUCKLE VINE

Japanese honeysuckle (Lonicera japonica Thunb.), introduced to the United States, and the native coral honeysuckle (Lonicera sempervirens L.) were compared to determine how intrinsic differences in their growth characteristics would affect their response to atmospheric carbon dioxide enrichment. Plants of both species grown from cuttings were harvested after 54 days of growth in controlled environment growth chambers at 350, 675, or 1,000-mu-l/liter CO2. The biomass of Japanese honeysuckle was increased 135% at 675-mu-l/liter CO2 and 76% at 1,000-mu-l/liter CO2 after 54 days. Morphologically, the main effect of CO2 enrichment was to triple the number of branches and to increase total branch length six times. Enhanced and accelerated branching also increased total leaf area 50% at elevated CO2 concentrations. In coral honeysuckle, total biomass was only 40% greater in the elevated CO2 treatments. Branching was quadrupled but had not proceeded long enough to affect total leaf area. Main stem height was increased 36% at 1,000-mu-l/liter CO2. The much less significant height response of other woody erect growth forms suggests that vines may increase in importance during competition if atmospheric CO2 concentrations increase as predicted. The impact of Japanese honeysuckle in the United States may become more serious.