[Effects of sub-low temperature and drought stress on characteristics of photosynthetic and fluorescence kinetics in tomato leaves].

By using tomato as material potted in climatic chamber, the photosynthetic characteristics and allocation of energy and electron flow were studied under sub-low temperature (8-15 °C) and drought (55%-65% of field moisture capacity) conditions. The results showed that the photosynthetic pigment content declined under sub-low temperature stress, but increased under drought stress. Both sub-low temperature stress and drought stress significantly decreased the intercellular CO2 concentration, stomatal conductance and photosynthetic rate, and increased the stomatal limita- tion, which further decreased or increased under simultaneous treatment of sub-low temperature and drought stress. The photorespiration significantly increased under separate treatment of sub-low temperature and drought stress, but decreased under simultaneous treatment. The stress declined the Fo, Fv/Fm and Fv'/Fm', which showed the damage of photosystem. It increased the distribution of energy to PS I and declined the photochemical efficiency, total electron flow and alternating electron flow. Thermal dissipation and the ratio of alternating electron flow were elevated to dissipate the excess energy. Compared with separate treatment of sub-low temperature and drought stress, the simultaneous treatment made thermal dissipation higher, but did not make alternating electrons flow further increase.