| Temperature and atmospheric CO2 concentration increases are the main trends of climate change.The increases of atmospheric CO2 concentration and temperature directly affect crop leaf photosynthesis,hence crop yield.Wheat is one of the most important staple food crops in China.Different wheat varieties may have different responses to elevated CO2 and increased temperature.Quantitative analysis of the response of photosynthesis of different winter wheat varieties to elevated atmospheric CO2 concentration and increased temperature is important for further development of crop growth models for assessing impacts of climate change on crop productivity In this study,an experiment was conducted during 2017-2018 in a Free Air CO2 Enrichment and Temperature increase(T-FACE)platform located at Kangbo Village(31°30’N,120°33’E),Guli Town,Changshu City,Jiangsu Province.Three winter wheat varieties(Sumai 188,Xinnong 518 and Yangmai 16)were used in the experiment.Four treatments were set up in the experiment:control(CT),atmospheric CO2 concentration increased by 500 μmol mol-1(C+T),canopy temperature increased by 1.5-2.0℃(CT+),atmospheric CO2 concentration increased by 500μmol mol-1 and the canopy temperature increased by 1.5-2.0℃(C+T+)which simulates climate conditions in 2050.The An-Iinc and An-Ci curves of flag leaves with wheat varieties at growth stage were measured.Based on the experimental data,we quantitatively analyzed the effect of elevated atmospheric CO2 concentration and increased temperature on the photosynthetic parameters of different winter wheat varieties.The photosynthetic parameters include light-saturated photosynthetic rate(Ag,max),day respiration rate(Rd)and initial quantum efficiency of photosynthesis(s).The main results were summarized as follows.(1)There were significant interactions among CO2,temperature and varieties for Ag,max after heading stage.The increase of atmospheric CO2 concentration significantly increased Ag,max of Sumai 188 at the heading stage,but significantly decreased Ag,max of Sumai 188 at the grain-filling stage,but had no significant effect on Ag,max of Xinnong 518 and Yangmai 16 at the heading and grain-filling stage.The increase of temperature significantly increased Ag,max of Yangmai 16 at the heading stage,but had no significant effect on Ag,max of Sumai 188 and Xinnong 518 at the heading stage,but significantly decreased Ag,max of Sumai 188 at the grain-filling stage,and there was no significant effect of Ag,max of Yangmai 16 and Xinnong 518 at the grain-filling stage.The simultaneous increase of atmospheric CO2 concentration and temperature significantly increased the Ag-max of Sumai 188 and Yangmai 16 at heading stage,but significantly decreased Ag,max of Sumai 188 and Yangmai 16 at the grain-filling stage,and had no significant effect on Ag,max of Xinnong 518 at the heading stage and grain-filling stage.(2)There were significant interactions among CO2,temperature and varieties for Rd during the growth stage.The increase of atmospheric CO2 concentration significantly decreased the Rd of Sumai 188 during grain-filling stage,and significantly increased the Rd of Yangmai 16 at the heading stage,but had no significant effect on Rd of Xinnong 518 at the growth stages.Increased temperature significantly increased Rd of Xinnong 518 at jointing stage,and the Rd of Yangmai 16 at heading stage,significantly reduced the Rd of Yangmai 16 at jointing stage,but had no significant effect on Rd of Sumai 188 at different growth stages.The simultaneous increase of atmospheric CO2 concentration and temperature significantly increased the Rd of Sumai 188 at heading stage,Xinnong 518 at heading and grain-filling stage and Yangmai 16 at the jointing stage and heading stage.(3)There were significant interactions among CO2,temperature and cultivar forε during the growth stage.The increase of atmospheric CO2 concentration significantly increased ε of Yangmai 16 at jointing stage,and had no significant effect on ε of Sumai 188,Xinnong 518 and Yangmai 16 at the heading stage and grain filling stage.The increase of temperature significantly decreased the ε of Sumai 188 at the grain-filling stage,and had no significant effect on ε of Sumai 188,Xinnong 518 and Yangmai 16 at jointing stage and heading stage.The simultaneous increase of atmospheric CO2 concentration and temperature significantly decreased ε of Sumai 188 and Yangmai 16 at the grain-filling stage,and had no significant effect on the ε of Sumai 188,Xinnong 518 and Yangmai 16 at the jointing stage and heading stage.(4)TheAg,max of winter wheat varieties were significant increased with the increase of atmospheric CO2 concentration at the early growth stage,which was mainly related to the increase of CO2 concentration in leaves of different winter wheat varieties under increase of atmospheric CO2 concentration.The response of Ag,max in the leaves of different winter wheat varieties to the increase of atmospheric CO2 concentration was related to the difference of leaf nitrogen accumulation after heading.Elevated atmospheric CO2 concentration significantly increased the leaf Ci of Sumai 188,Xinnong 518 and Yangmai 16 at each stage,which resulted in significantly increased the Ag,max of Sumai 188 at jointing stage of and heading stage and Xinnong 518 and Yangmai 16 at jointing stage.Elevated CO2 concentration significantly reduced Ag,max of Sumai 188 at the grain-filling stage,and had no significant effect on Ag,max of Xinnong 518 and Yangmai 16 after the heading stage.This may be related to the elevated CO2 decreased nitrogen accumulation in leaves of Sumai 188 at grain-filling stage,but it does not significantly reduce the nitrogen accumulation in leaves of Yangmai 16 after heading stage.(5)It is indicated that the increase of Ag,max in the heading stage of Yangmai 16 may be related to the increase of Ci/Ca,and the stomatal conductance is not the influencing factor of the decrease of Ag,max of Sumai 188 at the grain-filling stage under temperature increased.Increased temperature significantly increased the stomatal conductance of leaves of Sumai 188,Xinnong 518 and Yangmai 16 at heading stage,but had no significant effect on the stomatal conductance of the leaves of Sumai 188,Xinnong 518 and Yangmai 16 at grain-filling stage.Similarly,increased temperature significantly increased the Ci and Ci/Ca of the leaves of Yangmai 16 at heading stage and the Ci and Ci/Ca of the leaves at the heading and grain-filling stages,and there was no significant effect of Ci and Ci/Ca of leaves of Yangmai 16 at grain-filling stage.Furthermore,by analyzing the linear relationship between the nitrogen accumulation of leaves and Ag,max of Sumai 188,Xinnong 518 and Yangmai 16.It was found that the increased temperature did not change the quantitative relationship between the nitrogen accumulation of leaves and the Ag.max of of Xinnong 518 and Yangmai 16,indicating the effect of increased temperature on Ag,max of Xinnong 518 and Yangmai 16 at growth stages was related to the changes in nitrogen accumulation.The elevated temperature changed the slope of the linear relationship between the nitrogen accumulation of leaves an Ag,max of Sumai 188,indicating that the effect of increased temperature on the Ag,max of Sumai 188 may not only be related to the nitrogen accumulation of leaves.The decrease of nitrogen accumulation of leaves was one of the reasons for the significant decrease Ag,max of Sumai 188 at grain-filling stage under elevated temperature.(6)The Ag,max of winter wheat varieties were significant increased with the increase of atmospheric CO2 concentration and temperature,which was mainly related to the increase of CO2 concentration in leaves of different winter wheat varieties under increase of atmospheric CO2 concentration and temperature.The response of Ag,max in the leaves of different winter wheat varieties to the increase of atmospheric CO2 concentration and temperature was related to the difference of leaf nitrogen accumulation after grain-fill stage.The simultaneous increase of CO2 concentration and temperature significantly increased the Ci and Ci/Ca in the leaves of Sumai 188 and Yangmai 16 at heading stage,resulting in a significant increase in Ag,max of Sumai 188 and Yangmai 16 at the heading stage.The simultaneous increase of CO2 concentration and temperature significantly reduced the Ag,max of Sumai 188 and Yangmai 16 at grain-filling,and had no significant effect on Ag,max of Xinnong 518 at grain-filling stage.This may be related to the simultaneous increase of CO2 concentration and temperature,which significantly reduced the nitrogen accumulation in the leaves of Sumai 188 and Yangmai 16,but did not significantly reduce the nitrogen accumulation in the leaves of Xinnong 518 at grain-filling.The results of this study indicate that breeding varieties with strong photosynthesis ability and increasing nitrogen application after heading will be effective measures for winter wheat production to cope with future climate change. |
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