Physiological Responses Of Populus Alba 'Berolinensis' L And Syringa Oblata To Elevated O₃ Concentration And Drought

With the rapid development of modern industrialization and urbanization,the ozone concentration in the surface layer of the earth is increasing.At the same time,affected by global climate change,land surface rainfall decreased and evaporation increased,the global drought area is also increasing.Under the background of global warming,ozone and drought stresses are often in cooccurrence.In addition,as city is the special area interfered most frequently by human,urban trees are not only threatened by greenhouse gases,especially ozone,but also suffer from drought stress.In this study,Populus alba and Syringa oblate seedings,the main urban tree species,were exposed to elevated O₃ concentrations(80 nmol·mol^-1)and drought stresses by using open top chambers?OTCs?.The growth parameters and photosynthetic physiological parameters were determined by outdoor experiment and the physiological indexes and BVOCs emission were measured in laboratory,in order to research the physiological response on P.alba and S.oblata in the interaction in ozone and drought and both compounds,reveal the effects of the elevated ozone concentration and drought stress on urban trees and the adaptation mechanism.The main results were as follows in details:?1?Growth response:Under ozone stress,there were obvious black patches on foliar of P.alba.The main symptom of S.oblata was that the leaves became brown.Under drought treatment,visible foliar injury of P.alba and S.oblata were small and dark green.Under the combined stress,the leaf morphology was similar to that under drought stress.Through the electron microscope,under elevated O₃,the arrangement of leaf cells of P.alba was disordered,the morphology of palisade tissue and spongy tissue changed,the upper epidermis and spongy tissue were increased by 55.5%and37.7%respectively,and the thickness of the lower epidermis and palisade tissue decreased by 12%and 0.7%respectively.The interaction of ozone and drought did not interact with the height of P.alba and S.oblata,and drought was the main factor inhibiting height.The combined action of ozone and drought has significant interaction with water content in leaves of P.alba,which is antagonistic to each other.Water content is between ozone and drought.The leaf water content and relative water content of S.oblata were not significantly affected.?2?Photosynthetic physiological change:Under the combined action of ozone and drought,the Pn of P.alba showed an obvious interaction,and showed antagonism,drought has slowed ozone's decline in Pn.There was no significant interaction in S.oblata.Under ozone treatment,the Pn of P.alba decreased significantly,and the intercellular carbon dioxide concentration?Ci?increased significantly compared with the control,and the stomatal conductance?Gs?and transpiration rate?Tr?decreased.Under different treatments,the Pn,Gs,Ci and Tr showed the trend of rising first and then decreasing.Effective quantum yield of combined treatment on the?PS?of P.alba have significant interaction,showed antagonistic action,Fv/Fm had no significant difference among different treatments.There was no photoinhibition in S.oblata,and there was no significant interaction between?PS?under the combined action,which was significantly higher than that of control under drought stress and combined stress.Under ozone stress,Fv/Fm were significantly higher than drought stress and combined stress.Ozone stress and drought stress under the combined effect of light and pigment content in P.alba and S.oblata showed significant interaction,performance antagonism,significantly increased photosynthetic pigment content,degradation of the degradation rate of composite processing rate of single factor.S.oblata showed synergistic effects and the content of light and pigment increased under single factor stress.?3?Adverse environmental physiological indexes:The combined effects of ozone and drought on the MDA content of S.oblata had significant interaction.The interaction results showed that drought decreased the increase of MDA content in leaves under ozone stress,In the treatment of 60d,the MDA content in each group was significantly higher than that in the control group,thus indicating that compound stress had a positive effect.The soluble protein content in P.alba treated with ozone and drought has an obvious interaction,which is antagonistic.Drought alleviated the degradation of soluble protein in leaves by ozone.Under the combined stress of ozone and drought,the change of soluble protein content is between ozone single factor and drought single factor,and has significant antagonistic effect on the treatment of 60d.Drought stress had more effect on ABA of S.oblata than ozone stress,and compound stress had significant interaction with antagonism.?4?BVOCs emission:the main material in the discharge of P.alba was isoprene.Elevated O₃ concentration significantly inhibited the isoprene emission rate of P.alba.Ozone stimulation did not affect the main emission material of S.oblata.