The competition between winter rape (C3) and maize (C4) plants in response to elevated carbon dioxide and temperature, and drought stress

The aim of this study was to estimate the effects of drought stress under elevated CO2 and temperature on the competition between winter rape and maize plants. The experiment was conducted in a controlled-environment growth chamber at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry. Plants grown in monoculture (100:0) or in mixture (winter rape:maize, 50:50) irrigated and non-irrigated (drought stress), were exposed to ambient environment conditions day/night temperature 21/14 degrees C, CO2 - 350 ppm (CO2 T), and enhanced environment conditions - day/night temperature 30/23 degrees C, CO2 - 700 ppm (+CO2 T). Maize (C-4) grown in mixture with winter rape (C-3), had significantly smaller assimilating leaf area and produced less fresh mass at CO2 T and +CO2 T, as compared to monoculture, and water deficit strengthened the negative effect. Comparison of the data obtained for monoculture revealed that elevated CO2 and temperature in the conditions of sufficient moisture supply had significantly positive effect on maize assimilating leaf area (increased similar to 21%) and fresh mass accumulation (increased similar to 22%). Assimilating leaf area and fresh mass of winter rape and maize monocultures significantly decreased in response to water deficit both at CO2 T and +CO2 T. Water shortage had a stimulating effect on chlorophylls in leaves of winter rape in monocultures and mixtures. At +CO2 T and sufficient water supply, maize in monoculture and mixture with rape significantly reduced the content of chlorophyll a. Carotenoid content significantly decreased in maize leaves (monoculture and mixture) under +CO2 T in both irrigated or non-irigated substrates. Winter rape, in monoculture and mixture, accumulated significantly higher content of carotenoids under water deficit and ambient +CO2 T. However, a significant decrease in carotenoids was determined in rape leaves under +CO2 T. The elevated contents of ascorbic acid, total phenolics and antioxidant potential indicate high capacity of winter rape to counter oxidative stress.