The susceptibility of PS II of Lolium perenne to a sudden fall in air temperature—response of plants grown in elevated CO 2 and/or increased air temperature

Abstract

The effect of a sudden fall in air temperature from 20 to 5°C on fast kinetics of chlorophyll fluorescence, maximum yield of the photosystem II photochemical reactions (Fv/Fm), quantum yield of the photosystem II electron transport (Φ II), coefficients of photochemical (qP), non-photochemical quenching (qN) was studied in Lolium perenne using a modulated chlorophyll fluorescence technique. Before fluorescence measurement, the plants were cultivated in the treatments simulating the likely future climate characterized with elevated air temperature and CO 2 concentration and combination of both. On fast kinetics curves the risetimes of the I and D points characterizing the redox state of Q A were affected by lowering the air temperature. At 5°C both the I and D points were reached later than at 20°C. Also the I to D risetime was prolonged at 5°C and it was found significantly longer in plants cultivated in ambient +4°C temperature. While a significant difference was found in the area over the rising part of the fluorescence curve between 20 and 5°C, no difference was found in area over the relaxation curve part. Lowering of air temperature to 5°C had no effect on Fv/Fm values in control plants and in the plants cultivated in elevated CO 2 but brought significant decrease in plants cultivated in the ambient +4°C air temperature. Both Φ II and qP decreased with the temperature lowered to 5°C while the values of qN increased. The changes in fluorescence parameters indicated altered functioning of PS II at low temperature. The changes in parameters are discussed as a consequense of decreased enzymatic activity, decreased turnover of plastoquinone pool and photoinhibition.