Study On Stress Indices Of Quercus Variabilis Seedlings Based On Chlorophyll Fluorescence Parameters Under High Temperature And Drought

To explore the physiological response.of Quercus variabilis seedlings in different degrees of drought,high temperature and the composite stress,Quercus variabilis seedlings belonging to annual plants are selected as test materials.To begin with,water the seedlings to reach the saturated water.And then let the seedlings form different levels of soil moisture as a result of natural evapotranspiration which leads to different levels of drought stress(soil water content ranges from 4.1%to 30%)and high temperature stress(25 degrees Celsius for comparison,35-49 degrees Celsius for high temperature treatment).By measuring with the Mini-PAM chlorophyll fluorescence spectrometer chlorophyll fluorescence parameters(such as Fv/Fm,Y(Ⅱ),ETR,qP,qL,qN,NPQ,Y(NO)and Y(NPQ))of the Quercus variabilis seedling leaves in different extent of high temperature,drought and its composite stress,there are the following results after the analysis and processing of the test data.(1)The chlorophyll fluorescence parameters like Fv/Fm,Y(Ⅱ),qL and qN of the leaves of the Quercus variabilis leaves changes significantly with the decreasing soil water under the single drought stress..Fv/Fm,Y(Ⅱ)and qL values decline in the power exponent function as stress increases.However,the qL value in soil moisture drops(below 10%),the data appears to be discrete,while the qN value as the soil humidity decreases first rises slowly and maintain a high level,and then drops-rapidly when the soil humidity is below 10%.(2)In the appropriate natural environment,Fv/Fm and Y(Ⅱ)values as well as their relationships with soil water under different soil humidity are measured and modeled mathematically.Based on Fv/Fm and Y(Ⅱ)values,θ50 and θk are determined respectively.The degree of drought stress based on the soil water is divided into three levels,namely mild drought 9%-13%,moderate drought 6.5%-9%and severe drought 4%-6.5%.(3)The chlorophyll fluorescence parameters like Fv/Fm and Y(Ⅱ)of the leaves of the Quercus variabilis only subjected to high temperature stress changes obviously with the increase of the treatment temperature.The values of Fv/Fm and Y(Ⅱ)with the increase of temperature shows a declining trend of the Logistic curve with slow,fast and slow paces.(4)In the proper natural environment,different temperature treatments are implemented,Fv/Fm and Y(Ⅱ)values as well as their relationships with soil water under different temperature are measured and modeled mathematically.Based on Fv/Fm and Y(Ⅱ)values,values of T50 are respectively 59.4℃ and 47.5℃,which represent respectively high temperature indicators of PSII death and the deactivation.(5)The chlorophyll fluorescence parameters of oak leaves changes clearly with the increase of the degree of stresses when different degrees of high temperature and drought are conducted.All chlorophyll fluorescence parameters like Fv/Fm,Y(Ⅱ),ETR,qP of Quercus variabilis seedlings in different soil moisture.follow the Logistic curve simulation as the temperature increases,showing a declining trend of the Logistic curve with slow,fast and slow paces.However,the chlorophyll fluorescence parameters under different temperature treatments drop at divergent speeds.It declines faster when the soil moisture is higher and smaller when the soil moisture is lower.Moreover,if the soil water is lower it corresponds to the lower temperature when the declining speed of values of chlorophyll fluorescence parameters beginning to accelerate.The general changing tendency of qN,NPQ,Y(NO)and Y(NPQ)is as follows:when the temperature increases to a turning point,all relatively small values rise abruptly and achieve greater values,and then remain stable or decline.Additionally,the turning point of temperature decreases with the loss of the soil moisture.(6)Under different levels of soil humidity and temperature,Fv/Fm and Y(Ⅱ)values of Quercus variabilis seedlings in different soil moisture and their respective relationships with the temperature are determined and mathematical modeled.Based on Fv/Fm and Y(Ⅱ)values the temperature indicator of T’50 value can be calculated respectively.T’50 values of Fv/Fm and Y(Ⅱ)are not fixed but shows a trend of decline in power exponent function with the deepening of the degree of drought stress.According to the law of the power function,the corresponding three kinds of drought degree namely light(9-13%),moderate(6.5-9%),severe(4-6.5%)lead to an average of T’50 value.Now it is concluded that for Quercus variabilis seedlings in high temperature and drought stress critical temperatures are 47,46 and 42 degrees Celsius respectively and that the lethal temperatures are 56,53 and 48 degrees Celsius respectively.