Effects Of Elevated CO₂ Concentration On Photosynthesis Parameters And Monoterpenes Emission Of Schima Superba Seedlings

There are very few studies to explore the responses of plants under all of CO₂ scenarios about 430-480,580-720,720-1000,and more than 1000μmol·mol^-1 predicted by the IPCC（Intergovernmental Panel on Climate Change）Report under the background of elevated CO₂concentration in atmosphere.The BVOC（Biogenic Volatile Organic Compounds）with high chemical reactivity may promote photochemistry air pollution by affecting the chemical compositions of lower atmosphere.Additionally it also will influence the greenhouse effect and global environment changes,thus knowing the effect on BVOC emission by elevated CO₂concentration is helpful to understand the impact of future climate change on the atmosphere.In this study,one-year-old Schima superba seedlings were exposed to ambient,and 550,750,1000μmol·mol^-1 CO₂ concentration for one year from April,2019 to March,2020 to investigate the response of photosynthetic characteristics parameters,photosynthetic pigment contents,growth parameters and light response parameters by using Open Top Chambers（OTCs）.Monoterpenes emission was also investigated from August to Octorber,2019.The conclusions of the experiments were shown as follows:The net photosynthetic rate of Schima superba increased under elevated CO₂ concentration caused by improvment in intercellular CO₂ concentration and stomatal conductance before August,while this improvement in net photosynthetic rate decreased from August,2019 to Janurary,2020 under elevated CO₂ treatments maybe resulted from the decline of N contents in leaf,and the net photosynthetic rate decreased significantly in 550μmol·mol^-1 and 750μmol·mol^-1.Although stomatal conductance and transpiration rate increased under all elevated CO₂ concentration of Schima superba from May to July,2019,they were lower than the stomatal conductance and transpiration rate in ambient from November,2019 to March,2020,however water use efficiency under elevated CO₂ treatments was higher than ambient treatment during fumigation.The reduction among Chlorophyll a,Chlorophyll b and Carotenoids were 20.05%,18.13%,and 22.96%under 1000μmol·mol^-1,and 18.13%,14.12%,23.31%under 750μmol·mol^-1,respectively,which meant elevated CO₂concentration ruduced the content of photosynthetic pigment contents of Schima superba.Elevated CO₂ concentration enhanced the abilities of utilizing light energy casused by improvement in light saturation point（LSP）and apparent quantum yield（AQY）with reduction in light compensation point（LCP）of Schima superba seedlings.Biomass was increased by 41%、49.7%、87.36%compared to ambient under the treatments of 550μmol·mol^-1,750μmol·mol^-1,1000μmol·mol^-1 in March,2020,respectively.Above all,elevated CO₂ concentration improve the adaptablility for plants to climate change by increasing net photosynthetic rate which is beneficial to fix the increased CO₂in atmosphere and growth,water use efficiency and ability to use light energy.Elevated CO₂ concentration significantly decreased the monoterpenes emission rate of Schima superba by 48.62%and 51.39%respectively in 750 and 1000μmol·mol^-1 treatments compared with ambient treatment from August to Ocotober,2019.The decline of monoterpenes emission rate under elevated CO₂ concentration may contribute to reduction in stomatal conductance and leaf N content,with positively correlation between monoterpenes emission rate and stomatal conductance and leaf N content between August and Ocotober.