Responses And Physiological Mechanism Of Seedling Growth Of Two Provenances Of Quercus Variabilis To Drought Stress

In the 21 st century,drought is considered to be a serious threat to forest ecosystems.Quercus variabilis,as a relatively drought-resistant tree,is widely distributed,but there are significant differences in drought resistance in different regions.Therefore,it is particularly important to study the response of Q.variabilis to drought environment,in order to reduce the damage caused by the stress environment.Based on two provenances of Q.variabilis with significant difference in drought resistance,this paper carried out two experiments of water control(normal water supply,mild drought,moderate drought and severe drought)and natural drought.In order to explore its physiological response and drought reslistance mechanism,the growth,photosynthetic gas exchange parameters and chlorophyll fluorescence parameters of Q.variabilis pot seedlings with different gradients and stages were measured.The experiment were carried out in order to compare the difference of drought resistance of Q.variabilis seedlings,and compare the resilience of rehydration after drought,comprehensively analyze their physiological response under drought stress,and discuss the relationship between physiological mechanism and stress injury during drought stress,in order to lay a foundation for the study on the drought resistance mechanism of Q.variabilis.(1)With the aggravation of drought stress,the growth of Q.variabilis was inhibited,and the damage was most serious when the soil moisture content was 10%-15% of the field water capacity.In terms of provenance,the drought resistance and resilience of Q.variabilis in the Beipo Mountain provenance were stronger than those of Laojun Mountain provenance;With the extension of drought stress time,the growth of Q.variabilis seedlings can cope with drought stress by increasing the growth of the underground part and decreasing the growth of the aboveground part.(2)The decrease of chlorophyll content,relative water content,net photosynthetic rate(48.88%,60.82%,81.97%)of Laojun Mountain provenance after drought were significantly higher than those of Beipo Mountain provenance(32.72%,53.34%,73.97%),and the recoverydegree of Beipo Mountain provenance after rehydration(92.87%,95.20%,61.10%)were significantly higher than those of Laojun Mountain provenances(81.90%,46.50%,44.50%).The decrease of net photosynthetic rate was mainly caused by stomatal limitation.The gas exchange parameters changed a lot under severe drought stress;The response of main chlorophyll fluorescence parameters to drought stress was consistent with the gas exchange parameters,that was,severe stress caused the most serious damage to photosynthetic electron transport.(3)Protective enzymes(CAT,SOD and POD)played a synergistic role in increasing their activity and increasing MDA content to protect plants from drought stress.As the degree of stress deepened,beyond the maximum tolerance range of Q.variabilis seedlings,protective enzyme activity decreases,MDA content increases rapidly,and proline,soluble protein and soluble sugar content increased first and then decreased.After rehydration,drought stress was reduced,protective enzyme activity,soluble protein and soluble sugar were reduced,and all recovered to the CK level.(4)In the cultivation and management of Q.variabilis seedlings,the soil moisture content should be kept between 55% and 75% as far as possible.If the soil moisture content is lower than this level,serious loss of seedlings will be caused.