Differential Response And The Physiological Mechanism Of Photosynthetic Carbon Metabolism And Yield In Different Wheat Genotypes To Elevated CO₂ Concentration

The atmospheric carbon dioxide?CO₂?concentration has been increasing rapidly in the global climate change,and the elevated CO₂ will have a series of direct or indirect affects on the production of winter wheat.Facing the elevated CO₂ production environment how to ensure the stable and high yield of winter wheat?Studying the responses of different genotypes winter wheat cultivars to elevated CO₂and explore the mechanism characteristics of cultivar which had positive response to elevated CO₂,it is necessary to screen the cultivars which can use environmental resources efficiently.To study this issue,we conducted a Free air carbon dioxide enrichment system?FACE-system?to simulate elevated CO₂concentration in winter wheat cropping system at Changping in Beijing,from 2015 to 2018.Cultivars material include dwarf large-spike NL10,high stalk large-spike SH8675,high stalk medium-spike ZYM and multi-spike SLM.This experimental system combient with 6 elevated CO₂ treatments and 6ambient CO₂ treatments as main treatment,and 4 different cultivars as sub-treatment.The primary reaction,relative electron transfer rate,photosynthetic carbon assimilation,non-structural carbohydrates,key metabolic enzymes,and the grain yield data were measured in different treatments during winter wheat growth period,the effects of elevated CO₂ were analyzed.The main conclusions were showed as follow:?1?The primary reaction of all winter wheat cultivars were sensitive to elevated CO₂ at flowering stage.The primary reaction of high stalk large-spike cultivar SH8675 showed a positive response to elevated CO₂.Effective photochemical quantum yield of PSII(?_PSII)in flag leaf of SH8675 was increased by elevated CO₂,this is mainly due to elevated CO₂ decreased regulatory energy dissipation quantum yield(?_NPQ)and non-regulated energy dissipation quantum yield(?_NO),so the actual light energy conversion efficiency of SH8675 PSII was higher under elevated CO₂ environment.While,elevated CO₂ had no significant effect on?_PSII of dwarf large-spike cultivar NL10,because of elevated CO₂ decreased?_NPQ but increased?_NO.For high stalk medium-spike cultivar ZYM,elevated CO₂decreased?_PSII due to the increased?_NPQ so dissipation of excitation energy in the form of thermal energy was increased.?2?The maximum relative electron transfer rate(rETR_max)and half saturation irradiation?I_k?of NL10 and SH8675 flag were increased by elevated CO₂ at flowering stage.This is indicated that elevated CO₂ increased the relative electron transfer rate and optical tolerance of PSII in flag leaves of NL10 and SH8675.However,high stalk medium-spike cultivar ZYM was in the opposite,elevated CO₂decreased rETR_maxax of ZYM flag.In grain-filling stage the sensitivity of rETR of all cultivars to elevated CO₂ was reduced,only rETR_max and I_k of NL10 was increased by elevated CO₂.?3?Response of photosynthetic carbon assimilation of four winter wheat cultivars to elevated CO₂ is the net photosynthetic rate(A_g,max,?mol·m^-2·s^-1)was increased at jointing,flowering and grain-filling stage.And elevated CO₂ increased leaf area of NL10,SH8675 and ZYM at flowering stage,this is beneficial to the accumulation of photosynthetic carbohydrate.However,grain number leaf area ratio and grain weight leaf area ratio of NL10,SH8675 and ZYM were reduced by elevated CO₂,this is indicated that both the capacity of the load per leaf area and the contribution of per leaf area to the yield were decreased when plants grown under elevated CO₂ environment.?4?At flowering stage of winter wheat,elevated CO₂ increased SPS enzyme activity and sucrose content in leaves of SH8675,that is benefit for carbohydrate transfer to carbon pool.The SPS enzyme activity in SLM leaves was decreased by elevated CO₂,while the SS enzyme activity of SLM leaves was increased by elevated CO₂ which was beneficial to sucrose degradation and starch synthesis.Therefore,elevated CO₂ decreased sucrose content and increased the starch content of SLM leaves that caused a decreased transportation of NSC.?5?The carbohydrate transferred of NL10 showed a negative response to elevated CO₂,NSC accumulation and sucrose content of NL10 stem was decreased by elevated CO₂,which caused a decreased apparent transferred mass?ATM?,the ratio of transferred?AR?and contribution to grain yield?AC?of NSC.However,NSC accumulation and sucrose content of SH8675 and ZYM stem was increased by elevated CO₂.Therefore,ATM,AR and AC of NSC of SH8675 and ZYM stem were increased significantly.Elevated CO₂ decreased sucrose content but increased starch content of SLM leaves and stem,so accumulation of NSC in SLM leaves was increased.?6?Elevated CO₂ had no significant effect on grain number per spike,1000-grain weight and harvest index?HI?of four cultivars.However,in three years average grain-yield of NL10 and SH8675was 17.4%and 25.4%increased by elevated CO₂,this is caused by the increased spike number per unit area.And spike number per unit area of ZYM and SLM had no significant different between two CO₂concentration treatments,so elevated CO₂ had no significant effect on grain yield of ZYM and SLM.Above results indicated that spike number per unit area was the main factor determining grain yield when plants grown under elevated CO₂ environment.The results of this study showed that,compared with other cultivars,the light reaction,photosynthetic carbon assimilation and carbohydrate transferred of high stalk large-spike cultivar SH8675 had a positive response to elevated CO₂.And this provied a better theoretical significance and practical value for cultivating and screening future cultivars which are fit for elevated CO₂ production environment.