Physiological Characteristics of Betula halophila Seedlings under NaCl Stress

One year old seedlings of Betula halophila were subjected to the soil salinity stress with different NaCl concentrations.The leaf gas exchange parameters,chlorophyll content and osmolytes were studied at different times.The results showed that:(1)The net photosynthetic rate(Pn) decreased as soil NaCl concentration increased.When the concentration of NaCl was less than 1.6%,the main cause of Pn decreasing was that the non-stomatal conductance of B.halophila seedlings.When the concentration of NaCl was more than 1.6%,the main cause of Pn decreasing was that the stomatal conductance.The chlorophyll concentrations in leaves under 1% NaCl stress were higher than that of CK,and then decreased as NaCl concentration was more than 1%.The Chl a/b ratios were decreased as NaCl concentration increased.When NaC1 concentration was between 1.0% and 1.8%,relative conductivity(Rc),proline content(Pro),malonyldialdehyde content(MDA) and soluble sugar content(Ss) were going up,and when at 1.8%～2.2%,they were going down;(2)The different times had significant influence on stomatal conductance,intercellular CO2 concentration,transpiration rate,Rc and Ss,and had insignificant influence on Pn,Chl,Pro,MDA;(3)The seedlings of B.halophila can grow at 1.8% NaCl,but they died at 2.2% NaCl.