Stomatal Regulation Mechanism Of Drought Resistance Of 20 Tree Species In Temperate Forests Of Northeast China

The increase in frequency and intensity of drought worldwide has seriously affected the growth of trees,and even led to widespread forests mortality.The stomatal is the important link in terrestrial ecosystem of carbon-water coupling,which has made great contributed for carbon capture and maintain moisture balance.Hydraulic traits are the key to understand the plant functional responses during drought,so it is important to clarify stomatal regulation mechanism for understanding plant drought response and adaption strategy during drought.In order to better understand drought tolerance of plant with different plant functional types,and clarify stomatal regulation mechanism,here,we measured five pressure-volume（PV）traits（including leaf water potential at turgor loss point,cellular osmotic potential at full hydration,cellular bulk modulus of elasticity,leaf capacitance,and relative water content at turgor loss point）,two leaf structural traits（specific leaf area,SLA and leaf density,LD）,the parameters of stomatal response curves and photosynthetic response curves(Ψg_s88 andΨA₈₈)in 20 tree species（16 angiosperms and 4gymnosperms）in a temperate mixed forest at the Maoershan Forest Ecosystem Research Station,Northeast China.The main results are as follows:（1）Angiosperms had significant greater RWC_tlp and lower C_leaf than gymnosperms,indicating that RWC_tlp and C_leaf may be the good indicators of leaf drought tolerance in temperate mixed forest in Northeast China.Within angiosperms,TLP andπ₀ were significantly and negatively correlated with LD,but positively correlated with SLA;whileεwas negatively correlated with SLA.However,the opposite trends between PV traits and leaf structural traits were observed between gymnosperms and angiosperms,which might be attributed to the difference in drought response and adaptation strategies.（2）Angiosperms had significant less negativeΨg_s88 than gymnosperms,indicating that angiosperms close stomata earlier while gymnosperms could keep stomata opening for longer time to maintain photosynthesis during drought.According to the sequence ofΨg_s88 and TLP,we found that stomatal closure occurred after turgor loss point of most tree species,indicating that turgor loss induced by drought caused stomatal closure.Within angiosperms,Ψg_s88 andΨA₈₈were significantly and positively correlated with TLP,π₀ and SLA,but negatively correlated withεand LD.However,there was no significant relationship between stomatal traits and hydraulic traits in gymnosperms.These results showed that there is a significant coordinate relationship between stomatal and hydraulic traits for angiosperms,however,the influencing factors of that for gymnosperms need to be further studied.These findings indicated that two functional types adopt different stomatal regulation mechanisms.（3）Ψg_s88 was significantly and positively correlated with TLP and SLA but negatively correlated with LD across species.The results indicated that there were different strategies for plant of iso/anisohydry to cope with drought stress.Tree species that tend to be isohydric behavior had less investment to maintain turgor pressure and had relatively sensitive stomata to drought.Stomatal closure occurred within a narrow range of water loss is beneficial to water conservation and prevent hydraulic dysfunction.On the contrary,species that tend to be anisohydric behavior had greater investment in leaves to maintain stomatal opening and photosynthetic gas exchange in a wider range of water loss.The objectives of this study were to search the best indicators of leaf drought tolerance at local scale,and to explore the correlation between PV hydraulic traits and leaf stomatal or structural traits of 20 tree species with different functional types（angiosperm vs.gymnosperm）in a Chinese northeastern temperate mixed forest.These work will help providing a reference for revealing the adaptation mechanism of forest ecosystem under future climate change.