The Indicators Research Of Quercus Variabilis Seedlings Of High Temperature Stress Under Different Drought Conditions

In this study,the potted Quercus variabilis seedlings of one year old were used as experimental materials to study its response for drought stress of different degrees through measuring the changes of chlorophyll fluorescence parameters such as Fv/Fm,Y（Ⅱ）,ETR,q P,q N,NPQ,Y（NO）and Y（NPQ）under high temperature and drought stress by Mini-PAM chlorophyll fluorescence monitor.The results of the study were as follows:（1）The chlorophyll fluorescence parameters of Quercus variabilis leaves had an obvious change after the high temperature and drought stress.The values of Fv/Fm,Y（Ⅱ）,ETR and q P decreased with the increasing of the temperature,and submitted to Logistic curves law.（2）T₅₀ was sensitive to high temperature and drought stress as a temperature indicator of PSⅡ inactivation induced by stress.The T₅₀ which obtained through the value of Y（Ⅱ）could be more sensitive to indicate the temperature of PSⅡ inactivation.（3）The T₅₀ which obtained through the value of Y（Ⅱ）didn’t have an obvious change with the increase of treatment time.It shows that T₅₀ tends to stabilize after 1h of high temperature stress and then doesn’t have an obvious change with the time increase of high temperature stress.With the deepening of drought,the tolerance of Quercus variabilis seedlings to high temperature stress decreased gradually,and the temperature T₅₀ of PSⅡ inactivation is different in different drought degree.The temperature T₅₀ were 50.3℃、48.6℃、39.9℃ when processed in mild drought stress,moderate drought stress and severe drought stress treatment.（4）The temperature T₅₀ was 39.9℃ when processed in severe drought stress treatment,it was close to the value of T₅₀ which obtained through high temperature stress of Quercus variabilis detached leaves.It shows that the seedlings of Quercus variabilis couldn’t absorb moisture from the soil under severe drought and its stress level was equal to the stress level of detached leaves.（5）Under the high temperature and drought stress,the value of q N,NPQ,Y（NO）and Y（NPQ）would increase with different degrees.q N,NPQ,Y（NO）and Y（NPQ）had a temperature 45 ℃ of turning point under mild drought stress,when Quercus variabilis leaves started self-protection.With the deepening of drought,the damage of Quercus variabilis leaves was gradually increased under high temperature stress,and the temperature of turning point would advance accordingly.