The Response Mechanism Of Tea Plant To Elevated Atmospheric CO₂ Concentration And Temperature

As the most important greenhouse gas,the increase of CO2 concentration in the atmosphere leads to a significant rising in the surface temperature of the earth.It is estimated that the atmospheric CO2 concentration will reach to 780?mol/mol by the end of this centuryand the global average surface temperature will warm up 1.5-5.0?.As CO2 is the raw material of plant photosynthesis,and temperature affects the activities of enzymes related to photosynthesis,that making photosynthesis,as well as plant primary metabolism and secondary metabolism closely linked.Theanine,tea polyphenol and caffeine,three secondary metabolic,are the main quality components of tea plant.Theanine synthase gene has relationship with theanine in tea leaves;phenylalanine ammonialyase gene and chalcone synthase gene have relationship with tea polyphenol;caffeine synthase gene,inosine monophosphate dehydrogenase gene and s-adenosylmethionine synthase gene have relationship with caffeine.Elevated atmospheric CO2 concentrations(648-658 ?mol/mol)and elevated temperature(+0.57?)were investigated in this study using cultivar'Longjing-changye' as the material by open-top chambers.Photosynthetic parameters,chlorophyll fluorescence parameters,chlorophyll content,theaninet,tea polyphenol,caffeine content,as well as related genes expression under different treatments were measured.The effects of elevated atmospheric CO2 concentration and temperature on photosynthetic system and quality components in tea plant and the key enzyme genes related to the quality components were studied.Response mechanism of tea plant to elevated atmospheric CO2 concentration and temperature were explored.These provide theoretical basis for the processing of high quality tea,the reasonable cultivation of tea plants and the breeding of improved varieties in the future climate change.The conclusions as follows:(1)Elevated CO2 concentration,elevated temperature,both CO2 concentration and temperature increase can significantly increase the chlorophyll fluorescence parameters in tea leaves compared with the control.All treatments can increase the chlorophyll a,chlorophyll b and total chlorophyll content in tea leaves,while reduce the chlorophyll a/b,and both CO2 concentration and temperature increase has significant difference with the control.By improving the structure of PS ? and increasing the chlorophyll content,elevated CO2 concentration and elevated temperature can increase photosynthetic efficiency in tea leaves significantly.CO2 concentration and temperature increase together showed a synergistic effect.(2)Elevated CO2 concentration,elevated temperature,both CO2 concentration and temperature increase can significantly reduce the content of amino acids and caffeine in tea leaves compared with the control,while the content of polyphenols and the ratio of polyphenols and amino acids increase.The quality of raw material in traditional green tea producing areas will be adversely affected,while the quality of raw material of black tea producing areas will be beneficial effects,and the insect resistance of tea plants may be improved.Especially both CO2 concentration and temperature increase has the greatest impact.(3)Elevated CO2 concentration,elevated temperature,both CO2 concentration and temperature increase can decrease the relative gene expressions of TS,TIDH and TCS in tea leaves compared with the control,while PAL and CHS increased.Elevated CO2 concentration,both CO2 concentration and temperature increase can increase the gene expression levels of SAM in tea leaves,which was decreased with elevated temperature treatment.(4)The free amino acid,tea polyphenol,caffeine content in tea leaves and their corresponding key enzyme genes relative expression correlation analysis showed that:The relative expression of TS gene was significantly positively correlated with the content of theanine.For the content of tea polyphenol,the relative expression of CHS gene was positively correlated with it,while the relative expression of PAL gene has no significant correlation.For the content of caffeine,the relative expressions of TIDH and TCS genes were significantly correlated with it,while SAM gene showed a significant negative correlation.