Because of its ability to induce contact dermatitis, the establishment and spread of poison ivy is recognized as a significant public health concern. In the current study, we quantified potential changes in the biomass and urushiol content of poison ivy as a function of incremental changes in global atmospheric carbon dioxide concentration (CO₂). We also examined the rate of new leaf development following leaf removal to simulate responses to herbivory as functions of both CO₂ and plant size. The experimental CO₂ values (300, 400, 500. and 600 µmol mol⁻¹) corresponded approximately to the concentration that existed during the middle of the 20th century, the current concentration and near and long-term projections for this century (2050 and 2090), respectively. Over 250 d, increasing CO₂ resulted in significant increases in leaf area, leaf and stem weight, and rhizome length relative to the 300 µmol mol⁻¹ baseline with the greatest relative increase occurring from 300 to 400 µmol mol⁻¹. There was a nonsignificant (P  =  0.18) increase in urushiol concentration in response to CO₂; however, because of the stimulatory effect of CO₂ on leaf biomass, the amount of urushiol produced per plant increased significantly for all CO₂ above the 300 µmol mol⁻¹ baseline. Significant increases in the rate of leaf development following leaf removal were also observed with increasing CO₂. Overall, these data confirm earlier, field-based reports on the CO₂ sensitivity of poison ivy but emphasize its ability to respond to even small (∼ 100 µmol mol⁻¹) changes in CO₂ above the mid-20th century carbon dioxide baseline and suggest that its rate of spread, its ability to recover from herbivory, and its production of urushiol, may be enhanced in a future, higher CO₂ environment.

Nomenclature: Poison ivy, Toxicodendron radicans, (L.) Kuntze TOXRA