Photosystem II photochemical efficiency and photosynthetic capacity in leaves of tea plant (Camellia sinensis L.) under winter stress in the field

Abstract

The effects of winter stress on photosynthesis of the tea plant (Camellia sinensis L.) were determined over the course of a year. Changes in gas exchange and chlorophyll fluorescence parameters largely tracked seasonal changes of temperature, precipitation, and atmospheric vapor pressure deficit. Intrinsic photosystem II (PSII) efficiency (estimated from the ratio of variable over maximal chlorophyll fluorescence, Fv/Fm) was at maximal levels (0.80–0.83) during the summer, then decreased in the fall and remained below 0.6 from January to March. The low levels of Fv/Fm in the winter were accompanied by the strongest quenching of maximal (Fm) and initial (Fo) fluorescence, presumably reflecting engagement of photoprotective thermal energy dissipation. Net photosynthetic rate, transpiration rate, and stomatal conductance were highest in the summer and lowest from late fall to early spring. These data suggested that PSII photochemical efficiencies and photosynthetic capacity of tea plant were limited under low temperature in the winter. On the other hand, a greater water use efficiency, lower light compensation point, and lower light intensity at which photosynthesis became saturated might be advantageous for tea plants acclimated to the lower precipitation levels and light intensities of winter. Analysis of the relationships between temperature or humidity and photosynthetic variables suggested that tea plants might benefit from irrigation in winter.