Effects of high temperature on photosynthetic capacity in the leaves of creepers

Abstract

High temperature induces structural and physiological damage to plants. However, studies on the effects of constant high temperature on climbing plant species are limited. To estimate the response of photosynthetic capacity of two creeper species, Parthenocissus tricuspidata (Sieb. et Zucc.) and Parthenocissus quinquefolia (L.) Planch, to constant high-temperature treatment at noon, we measured photosynthetic pigments, gas exchange, and chlorophyll fluorescence parameters at 35, 40, and 45 °C (25 °C was the control treatment). High temperature significantly reduced photosynthetic pigment content, whereas carotenoid content showed the opposite trend. Net photosynthetic rate, stomatal conductance, transpiration rate, maximal quantum yield of PSII photochemistry, actual quantum yield of PSII photochemistry, and the coefficient of photochemical quenching all showed a decreasing trend, with increasing stress duration, whereas the non-regulated thermal energy loss and regulated thermal energy loss indexes increased. As temperature increased, intercellular CO2 concentration initially decreased and then increased. Non-stomatal restriction factors were the main cause of the decrease in photosynthetic rate when temperature exceeded 40 °C. These parameters recovered to pre-stress levels only in plants grown at 35 °C upon stress relief. P. quinquefolia showed higher photosynthetic heat resistance and resilience than P. tricuspidata. Our results revealed photosynthetic adaptation and recovery mechanisms in two creepers grown under high-temperature stress. Molecular and genetic approaches should be considered to gain deeper insight into the mechanism underlying high temperature adaptation in these two creepers.