Photosynthetic abilities in Cinnamomum camphora with high temperature stress

Photosynthesis is the most sensitive physiological process for environmental variation. To uncover any detriment of high temperature from photosynthesis on Cinnamomum camphora, the effects of high temperature stress on chlorophyll fluorescence transients, gas exchange rate, and water use efficiency in the plants treated with high temperature at 25℃ (the control), 35℃ and 45℃, respectively, were studied, and one-way analyses of variance was performed to analyze the effects of high temperature. Results showed that fluorescence intensity from O to P point in chlorophyll fluorescence transients in C. camphora declined as temperature increased. Fluorescence transient parameters significantly decreased by 21.7% (P < 0.01) in absorption flux per reaction center, 17.6% (P < 0.01) in trapped energy flux per reaction center, 38.8% (P < 0.01) in electron transport flux per reaction center, 60.2% (P < 0.01) in performance index based on absorption, and 26.9% (P < 0.01) in driving force based on absorption at 45℃. Compared to the control, dissipated energy flux per reaction center significantly increased by 13.5% (P < 0.05) and 78.4% (P < 0.01), respectively, under high temperature at 35 and 45℃. In addition, the photosynthetic rate, stomatal conductance, transpiration rate, and water use efficiency declined at 35 and 45℃. The maximum photosynthetic rate significantly reduced by 16.0% (P < 0.05) and 44.6% (P < 0.01), respectively, at 35 and 45℃. Therefore, high temperature stress reduced C. camphora photosystem Ⅱ efficiency by reducing light energy absorption, quantum yield, and electron transportation as well as by increasing the absorbed light energy dissipated as heat, which resulted in an assimilatory power reduction and photosynthetic rate decline.