Responses Of Isoprene And Monoterpene Emissions From Main Subtropical Trees To Multiple Environmental Factors

Isoprene(ISO)and monoterpenes(MTs)are the dominated components of biogenic volatile organic compounds(BVOCs),which play considerable roles not only in ecological functions,such as defending against stress and enhancing plant resistance,but also in environmental effects,i.e.,the formation of ozone and secondary organic aerosol,influencing global climate change,and so on.Global environmental changes,including atmospheric temperature,light,carbon dioxide(CO₂)concentration,precipitation pattern and nitrogen deposition,etc.,in turn will affect the physiology and biochemistry of plant,and further influence ISO and MT emissions.Currently,studies about the effects of environment changes on plant BVOC emissions are still scared in China,and specially fewer to studies about the interaction effects of different factors.Based on field survey and laboratory measurements of ISO and MT emissions from main subtropical trees,several plant species were selected as the research objects in this study.The simulated experiments were conducted in three scales,including field open top chamber(OTC),greenhouse and climate chamber,to determine the single or interaction effects of atmospheric temperature,light,CO₂concentration,soil water and nitrogen on ISO and MT emissions from plants.Plant photosynthetic indexes(i.e.,net photosynthetic rate(Pn)and stomatal conductance(g_s),etc.)and relevant enzymatic activity(i.e.,ISO synthase and MT synthase)were also measured to explore the physiological mechanisms of ISO and MT emissions in response to those environmental factors.The results can provide basic data for plant BVOC flux models and prediction of their influence on atmospheric environment.The main research contents and results are as follows:(1)Survey of ISO and MT emissions from main subtropical treesISO and MT emission rates of four dominant trees in Wuyi Mountain,namely Schima superba,Castanopsis eyrei,Cyclobalanopsis glauca and Cunninghamia lanceolata,were investigated in spring and autumn in 2018.The results showed that the highest ISO emission rate was appeared in C.glauca(68.54 pmol m^-2s^-1),and the highest MT emission rates for C.lanceolata(7478.36 pmol m^-2s^-1).Compared with the spring,the ISO and MT emission rates from S.superba,C.eyrei and C.lanceolata were significantly higher in the autumn,meanwhile,the proportion of limonene and3-carene significantly increased,while decreased(P<0.05)for?-pinene.Subsequently,six main subtropical trees in Dinghushan,namely Acmena acuminatissima,Acronychia pedunculata,Cryptocarya chinensis,Castanea henryi,Mallotus paniculatus and Schima superba,were measured for ISO and MT emission rates.The results showed that the highest ISO emission rate was appeared in A.acuminatissima(4842.76 pmol m^-2s^-1),and the highest MT emission rates for S.superba(3145.68 pmol m^-2s^-1).The MT emission rates were related with foliar temperature and g_s.?-pinene and?-pinene,accounted for over 83%of MTs,were the dominated MT species of the six plants in Dinghushan.(2)Effects of simulated elevated atmospheric temperature and CO₂concentration on plant ISO and MT emissions in the OTCFour main subtropical trees,namely Schima superba,Phoebe bournei,Cunninghamia lanceolata and Pinus massoniana,were studied for the effects of elevated atmospheric temperature and CO₂concentration on ISO and MT emissions with OTC simulation experiment.The results showed that the responses of plant ISO and MT emissions to elevated temperature(+4.5 ^oC)and CO₂concentration(+400ppm)varied with tree species and compounds.Generally,the single or interaction effects of elevated temperature and CO₂concentration inhibited the ISO emission from P.bournei,which might be due to the influences of plant photosynthesis and relevant enzymatic activity,and also indirectly related to malondialdehyde,proline and peroxidase.In addition,some results also showed that the ISO emission rates from S.superba and C.lanceolata,and the MT emission rates from P.massoniana increased under higher temperature and CO₂concentration.The highest ISO emission rate in the four tree species was appeared in C.lanceolata(104.36 pmol m^-2s^-1),and the highest MT emission rates for P.massoniana(9682.94 pmol m^-2s^-1).?-pinene,?-pinene and limonene were the dominated MT species in the four trees.In addition,ISO and MT emission rates varied significantly among the treatment time,which were related to foliar temperature,humidity and photosynthetically active radiation(PAR).(3)Effects of simulated soil water and nitrogen change on plant ISO and MT emissions in the greenhouseFour main subtropical trees,namely Schima superba,Ormosia pinnata,Cunninghamia lanceolata and Pinus massoniana,were studied on the effects of soil water and nitrogen change on ISO and MT emissions by soil column simulation experiment in the greenhouse.The results showed that the responses of plant ISO and MT emissions to soil water and nitrogen varied among tree species and compounds.Generally,ISO and MT emissions from S.superba and C.lanceolata increased under low soil water treatment,while decreased for the ISO emission from O.pinnata and the MT emissions from P.massoniana,which might relate to Pn,g_sand intercellular CO₂concentration.Nitrogen addition(80 kg N ha^-1y^-1)resulted in the enhancement of ISO and MT emissions from S.superba,O.pinnata,C.lanceolata and P.massoniana,which might be due to the promotion of plant photosynthesis and relevant enzymatic activity.In addition,there had no significant interaction effects of the soil water and nitrogen change on ISO and MT emissions for all trees in this study.The highest ISO emission rate in the four tree species was appeared in O.pinnata(18436.18 pmol m^-2s^-1),and the highest MT emission rates for P.massoniana(4578.75 pmol m^-2s^-1).?-pinene,?-pinene and limonene were the dominated MT species of S.superba,O.pinnata and C.lanceolata in this study,while?-pinene,?-terpinene and limonene for P.massoniana.Besides,significant seasonal variation of ISO and MT emission rates under different treatments were found,which was related to foliar temperature,humidity and PAR.(4)Effects of simulated temperature and light change on plant ISO and MT emissions in the climate chamberSubsequently,two main subtropical broad-leaf trees,namely Schima superba and Phoebe bournei,were selected to study the effects of precisely controlling temperature and light on ISO and MT emissions in the climate chamber.The results showed that ISO and MT emissions from S.superba and P.bournei were significantly affected by temperature and light.Generally,ISO and MT emission rates were lower in the low temperature and PAR,while increased with the increased of temperature or light intensity to some extent,then reaching the maximum emission rates at 40 ^oC and500?mol m^-2s^-1for S.superba,and at 30 ^oC and 1500?mol m^-2s^-1for P.bournei.This may be due to the promotion of plant Pn and g_s.However,the ISO and MT emission rates from P.bournei significantly decreased at 40 ^oC.In addition,?-pinene proportion for S.superba and P.bournei decreased(P<0.05)with the increased of temperature or PAR,while significantly increased for?-pinene.