Interactive effects of elevated CO2 and drought stress on leaf water potential and growth in Caragana intermedia

We studied the responses of leaf water potential (Ψw), morphology, biomass accumulation and allocation, and canopy productivity index (CPI) to the combined effects of elevated CO2 and drought stress in Caragana intermedia seedlings. Seedlings were grown at two CO2 concentrations (350 and 700 μmol mol−1) interacted with three water regimes (60–70%, 45–55%, and 30–40% of field capacity of soil). Elevated CO2 significantly increased Ψw, decreased specific leaf area (SLA) and leaf area ratio (LAR) of drought-stressed seedlings, and increased tree height, basal diameter, shoot biomass, root biomass as well as total biomass under the all the three water regimes. Growth responses to elevated CO2 were greater in well-watered seedlings than in drought-stressed seedlings. CPI was significantly increased by elevated CO2, and the increase in CPI became stronger as the level of drought stress increased. There were significant interactions between elevated CO2 and drought stress on leaf water potential, basal diameter, leaf area, and biomass accumulation. Our results suggest that elevated CO2 may enhance drought avoidance and improved water relations, thus weakening the effect of drought stress on growth of C. intermedia seedings.