Effects of NaCl Stress on Growth and Photosynthetic Characteristics of Lettuce(Lactuca sativa L.)Seedlings

Effects of NaCl stress in different concentration on growth and photosynthetic characteristics in leaves of lettuce seedlings were studied.The results showed that the plant height and root length were inhibited obviously.The content of chlorophyll decreased with the NaCl concentration and treated time.However,it increased under 50 mmol/L NaCl.The content of chlorophyll a dropped more rapidly than that of chlorophyll b.The net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)changed similarly with increasing salt stress,and all decreased.Stomatal conductance and intercellular concentrations of CO2(Ci)changed similarly under 50 mmol/L NaCl stress.The changes of stomatal conductance were contrary to intercellular concentrations of CO2 under 100-200 mmol/L NaCl.It was stomatal limitation that leading the photosynthesis declined in the treatments with lower concentrations.On the contrary,non-stomatal limitation was the dominative causation in the treatments with higher concentrations.