Isoprenoid Release From Castanopsis Carlesii And Schima Superba Under Ozone Stress And Its Effect On Ozone Formation Potential

Isoprenoid（mainly including isoprene and monoterpenes）is the most important class of biogenic volatile organic compounds（BVOCs）,and plays an important role in atmospheric environment.Rising surface O₃affects the release of isoprenoid,which form O₃in a series of photochemical reactions with NOx.In this study,the effects of high concentration O₃stress on plant isoprenoid release were simulated,and the influencing factors were analyzed in combination with related physiological indexes,which provided theoretical basis for the response of plant BVOCs release to O₃under the background of increasing near surface O₃concentration in the future and the mechanism of BVOCs on O₃formation.In this study,two-year-old Castanopsis carlesii and Schima superba were used to simulate high concentration O₃stress by open top chamber（OTC）.The test is divided into acute O₃stress（8 h and 16 h）and chronic O₃stress（4 months）.In the acute O₃stress test,O₃-CK（atmospheric background concentration,40～50 ppb）,O₃-250（O₃concentration 250 ppb）and O₃-500（O₃concentration 500 ppb）were set up.Three treatments,O₃-CK（atmospheric background concentration,60～70 ppb）,O₃-100（O₃concentration 100 ppb）and O₃-150（O₃concentration 150 ppb）,were set up in chronic O₃stress experiment to study the effects of high concentration O₃stress on plant isoprenoid and its O₃formation potential（OFP）,photosynthetic parameters and related physiological indexes.The main results are as follows:（1）Under acute O₃stress,the release rates of monoterpenes from C.carlesii and S.superba increased with increasing O₃concentration,which were higher than those in the control group,and reached the highest values under O₃-250 treatment(52.72 pmol m^-2s^-1and 208.61pmol m^-2s^-1,respectively).The response of isoprene was inconsistent(increased O₃concentration,The release rate of isoprene from C.carlesii decreased,and isoprene significantly decreased with the stress time.The release rate of S.superba isoprene was higher at 8 h under O₃stress than that in control group,and reached its peak at O₃-250 treatment(3.16 pmol m^-2s^-1),which was lower at 16 h under O₃stress than that in control group).Monoterpenes is the main isoprenoid,andα-pinene,limonene,3-carene account for the largest proportion of monoterpene components.This was mainly due to the change of stomatal conductance and net photosynthetic rate caused by O₃in C.carlesii and S.superba,which significantly affected the activities of monoterpene synthetase,isoprene synthetase and superoxide dismutase.（2）Under chronic O₃stress,the release rate of monoterpenes increased under one-month,two-month and three-month treatments,while the release rate decreased under four-month treatments.The isoprene response is inconsistent.With the extension of stress time,the release rate of isoprene increased significantly at O₃-100 treatment for 4months and reached the highest value(349.81 pmol m^-2s^-1).The release rates of monoterpenes and isoprene from S.superba increased,and both reached significant levels under O₃-100 treatment.The isoprenoid mainly release monoterpenes,of whichα-pinene and 3-carene account for a large proportion.In general,increased O₃concentration and prolonged stress time resulted in degradation of photosynthetic pigments,decreased photosynthesis,significant changes in soluble sugars,starch,monoterpene synthetase,isoprene synthetase and superoxide dismutase,and thus affected the release of isoprene.（3）Under acute and chronic O₃stress,isoprenoid odor OFP of C.carlesii and S.superba increased with low concentrations（O₃-250 and O₃-100）,indicating that low concentrations were more conducive to O₃formation.The actual O₃concentration was lower than estimated.Under acute O₃stress,C.carlesii and S.superba were mainly BVOCs/NO_X<4.O₃generation is mainly regulated by BVOCs.Chronic O₃stress in BVOCs/NO_X<4,4<BVOCs/NO_X<15,BVOCs/NO_X>15.O₃generation is regulated by BVOCs,NO_Xand both.