Effects Of Short-term High Temperature,doubled CO₂ Concentration And Foliar Ontogeny Stages On Release Of Monoterpenes And Photosynthetic Physiology On Cinnamomum Camphora

Cinnamomum camphora,as an important release source of BVOCs which have important physiological and ecological functions,is widely distributed in subtropical regions and plays an important role in urban landscape and ecosystem in southern China.Therefore,in order to study monoterpenes emission rate and photosynthetic characteristics of C.camphora leaf in different stages,and monoterpenes emission rate and photosynthetic physiology of mature leaves to short-term high temperature and atmospheric CO₂ concentration,the photosynthetic characteristics and monoterpenes emission rate of C.camphora leaves were determined in different seasons.Besides the response patterns of monoterpenes emission rate and photosynthetic characteristics of mature leaves to short-term high temperature and atmospheric CO₂ concentration were determined in this experiment.The results showed:（1）Mainly monoterpenes from C.camphora were careen and ocimene.The parameters of net photosynthesis rate（P_n）,stomatal conductance（G_s）,transpiration rate（T_r）and intercellular CO₂concentration（C_i）in three foliar ontogeny stages were significant different measured under standard conditions,and highest and lowest were found in mature and old foliage respectively.However highest total monoterpenes emission rate（E）were found in young foliage,and the lowest emission rate in mature foliage.（2）The response tendency of total monoterpenes emission with light intensity was similar to photosynthesis-light intensity response curves under three foliar ontogeny stages,while the response to CO₂ concentration were no significant impacts on total monoterpenes emission.Mature foliage had highest initial quantum efficiency（α）,maximum net photosynthetic rate(P_nmax),maximum carboxylase activity of Rubisco(V_cmax),respiration rate under light（R_p）and light saturation point（LSP）.While the highest value for light compensation poin（LCP）and dark respiration rate（R_d）were found in young foliage.The highest value for capacity of photosynthetic electron transport(J_max)and lowest value for capacity of V_cmaxwere found in old foliage.This meant that old foliage had the lowest light energy utilization and there was excess light energy under strong light,which was probably also a regulatory mechanism for the evergreen plants to use excess light energy to maintain a certain temperature to overwinter.（3）The highest maximum monoterpenes emission rate(E_max)and lowest apparent quantum efficiency（β）for total monoterpenes emission were found in young foliage,however,lowest E_maxand highestβand true quantum yield（β_T）and for total monoterpenes emission were found in mature foliage.（4）Leaf only by a single short-term high temperature,P_n showed a decreasing trend with temperature rise,of which 48℃of the short-term high temperature caused irreversible damage to P_n;For T_r,it had a catalytic effect,but with the exception of 48℃,it caused irreversible damage to T_r,and the remaining temperature had a restorative effect on its influence;The short-term high temperature of43℃and 48℃had a catalytic effect on C_i,and there was no irreversible damage;The effect of G_s on short-term high temperature was similar to P_n;There was no significant effect on the content of SOD,POD,MDA and chlorophyll in leaves（P>0.05）,but CAT content decreased significantly with temperature（P<0.05）;E increased with temperature.After temperature recovery,E was significantly higher than that before treatment,which 38℃and 43℃were significantly increased（P<0.05）,and no significant changes were observed in other temperature treatments.（5）The double CO₂ concentration significantly increased the P_n and C_i of the leaves（P<0.01）,but had no significant effect on the emission rate of T_r,G_s and E（P>0.05）.Under doubled CO₂concentration,the P_n of the leaves increased first and then decreased with increasing temperature,and the treatment at 48℃ caused irreversible damage to P_n;The variation of T_r and G_s with temperature was similar to that under normal CO₂ concentration.T_r increased gradually with temperature,and G_s was not affected;There was no significant change in C_i at 33℃ and 48℃（P>0.05）,but it decreased significantly at 38℃ and 43℃（P<0.01）.After rewarming,there was a significant decrease between treatments at each temperature（P<0.01）;Under doubled CO₂ concentration,there was no significant change in E under treatment at 33℃ and 38℃（P>0.05）,but the emission rate at 43℃ and 48℃ increased significantly（P<0.01）.After rewarming,the recovery pattern was similar to that of normal CO₂ concentration.To sum up,C.camphora leaf can regulate the emission rate of monoterpenes in different foliar ontogeny stages by adjusting photoelectron transport and photosynthetic efficiency,so as to meet the energy requirements of self-growth substances and to cope with various types of stress caused by changes in the seasonal environment.When be exposed to short-term high-temperature stress and doubled CO₂ concentration,the chlorophyll content,MDA and antioxidant enzyme activity of mature C.camphora leaves were not affected.And the mechanism by which C.camphora resisted external short-term high temperature and doubled CO₂ concentration was mainly through adjusting the photosynthetic efficiency and monoterpenes emission rate,so as to cope with the various stresses brought about by the external short-term high temperature and doubled CO₂ concentration.