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Leaf‐Level Physiology, Biomass, and Reproduction of Phytolacca americana under Conditions of Elevated CO2 and Altered Temperature Regimes

The effects of increasing air temperature and changing daily temperature regime under conditions of elevated CO2 on the physiology, biomass, and reproduction of a C3 plant species were investigated. Phytolacca americana L. (Phytolaccaceae) was grown under either ambient (370 μmol mol−1) or elevated (700 μmol mol−1) CO2 at three air temperature regimes (day/night temperatures of 26°/20°C, T1; 30°/24°C, T2; and 28°/24°C, T3). Length of day/night temperature exposure was adjusted so that average daily temperature was 22°C in T1 and 26°C in T2 and T3. Daily temperature regime was different for T2 and T3: plants in T2 experienced a higher maximum daily temperature but for a shorter daily duration than plants in T3. Elevated CO2 increased photosynthetic rate, total biomass, and root‐to‐shoot ratio (RSR) and decreased stomatal conductance and transpiration as well as allocation to reproduction. In contrast, elevated temperatures had no effect on photosynthetic rate, stomatal conductance, or total biomass, but they decreased RSR and increased transpiration, reproductive biomass, and allocation. Both elevated CO2 and increased temperatures advanced timing of flowering. The plant‐level transpiration rate exhibited a unique response to each of the daily temperature regime treatments. These results indicate that elevated CO2 and increased temperatures elicit different responses at the physiological and whole‐plant levels in P. americana, with little interaction between the CO2 and temperature effects. Furthermore, some evidence indicates that a changing daily temperature regime may be an important factor determining plant responses to warming temperatures and should be incorporated into predictions of plant and ecosystem responses to future climate change.