Responses of Photosynthetic and Defence Systems to High Temperature Stress in Quercus suber L Seedlings Grown under Elevated CO2

Abstract

Abstract: Growth in elevated CO2 led to an increase in biomass production per plant as a result of enhanced carbon uptake and lower rates of respiration, compared to ambient CO2‐grown plants. No down‐regulation of photosynthesis was found after six months of growth under elevated CO2. Photosynthetic rates at 15°C or 35 °C were also higher in elevated than in ambient CO2‐grown plants, when measured at their respective CO2 growth condition. Stomata of elevated CO2‐grown plants were less responsive to temperature as compared to ambient CO2 plants. The after effect of a heat‐shock treatment (4 h at 45 °C in a chamber with 80% of relative humidity and 800–1000 tmol m‐2 s‐1 photon flux density) on Amax was less in elevated than in ambient CO2‐grown plants. At the photochemical level, the negative effect of the heat‐shock treatment was slightly more pronounced in ambient than in elevated CO2‐grown plants. A greater tolerance to oxidative stress caused by high temperatures in elevated CO2‐grown plants, in comparison to ambient CO2 plants, is suggested by the increase in superoxide dismutase activity, after 1 h at 45 °C, as well as its relatively high activity after 2 and 4 h of the heat shock in the elevated CO2‐grown plants in contrast with the decrease to residual levels of superoxide dismutase activity in ambient CO2‐grown plants immediately after 1 h at 45 °C. The observed increase in catalase after 1 h at 45 °C in both ambient and elevated CO2‐grown plants, can be ascribed to the higher rates of photorespiration and respiration under this high temperature.