| Climate change is mainly characterized by atmosheric CO2 concentration elevation and temperature increase,which has a direct effect on crop photosynthesis and productivity.Photosynthesis is a critical process for plant grown,it determinate grain yield directly.Previous studies on photosynthesis-light response mostly based on steady-state level,however,plant photosynthesis in natural never occur in steady-state conditions.When a leaf is exposed to a sudden increased light,the increase in photosynthesis shows a time delay.This effect restrict the improvement of lightfleck use efficiency and decrease crop potential assimilation.How does the dynamic photosynthesis of leaves change under the conditions of elevated CO2 concentration and temperature?This is one of the scientific question that need to be answered accurately to assess the impact of climate change on crop productivity and to identify how cultivars can crop with climate change.Wheat is one of the most important food crops in China,quantifying the effects of CO2 enrichment and temperature increase on dynamic photosynthesis of wheat cultivars may provide a reference for winter wheat to deal with climate change and cultivation management.In this study,winter wheat Sumai 188,Xinnong 518 and Yangmai 16 were used as the experimental materials.We designed four experimental treatments,that is,an untreated plot with ambient condition as control(CT),one with target atmospheric CO2 up to 500 ppm(C+T),one with warming of canopy temperature by 2℃ above ambient(CT+),and one with combined CO2 enrichment and warming(C+T+)to analyse the responses of dynamic photosynthesis of different wheat cultivars to elevated CO2 and increased temperature in T-FACE system established in Kangbo Village(31°30’N,120°33’E),Guli Township,Changshu Municipality,Jiangsu,China during 2017-2018.Using filed observation data,we quantitatively analyzed the respones of dynamic photosynthesis(net photosynthesis rate during the induction,induction time and lightfleck use efficiency)to CO2 enrichment and temperature increase of different wheat cultivars and the cause of these effects.The main research results were as follows:1.The effect of elevated CO2 and increased temperature on net photosynthetic rate during the induction is different between wheat cultivars and growth stage.C+T treatment significantly increased An of all cultivars at stem-elongating and heading stage,but had no significant effect of all cultivars at grain-filling stage.CT+treatment significantly increased An of Sumai 188 at stem-elongating and heading stage,but had no significant effect on Xinnong 518 and Yangmai 16.The An of all cultivars was significantly reduced at grain-filling stage.C+T+treatment increased An of all cultivars at stem-elongating and heading stage but decreased at grain-filling stage.The interaction effect was only in heading stage of Sumai 188.2.The effect of elevated CO2 and increased temperature on induction time is different between wheat cultivars and growth stage.C+T treatment prolonged the induction time of all cultivars at stem-elongating stage and significantly shortened the induction time of all cultivars at heading and grain-filling stage.CT+treatment significantly prolonged the induction time of Yangmai 16 at stem-elongating stage but had no significant effect on Sumai 188 and Xinnong 518;CT+treatment significantly shortened the induction time of Sumai 188 and Xinnong 518 at heading stage,but had no significant effect on Yangmai 16.The induction time of all cultivars was shortened at the grain-filling stage under CT+treatment.C+T+treatment prolonged the induction time of all cultivars at stem-elongating stage and shortened at heading stage.The induction time of Sumai 188 and Yangmai 16 was prolonged,but significantly shortened the induction time of Xinnong 518 at grain-filling stage.3.During a series of lightflecks,C+T treatment significantly reduced the lightfleck use efficiency(LUE)of Xinnong 518 and Yangmai 16 at stem-elongating stage;C+T treatment significantly improved LUE of Xinnong518 at heading stage.It had no significant effect on LUE of all cultivars at grain-filling stage under C+T treatment.CT+treatment significantly reduced LUE of Xinnong 518 and Yangmai 16 at stem-elongating stage.There was no significant effect on LUE of all cultivars at heading stage.The LUE of Sumai 188 was significantly reduced at grain-filling stage under CT+treatment.The C+T+treatment had no significant effect on LUE of all cultivars at stem-elongating and heading stage.The LUE of Sumai 188 and Yangmai 16 was significantly reduced,but had little effect on Xinnong 518 at grain-filling stage.4.After the irradiance increased suddenly to 1000 μmol m-2 s-1,the initial stomatal conductance(gsi)is negatively with the induction time,and the gsi has a threshold for the induction time limitation,it is independent of cultivars and treatments.Under C+T treatment and CT+treatment,the change of induction time were related to gsi of all cultivars before heading stage.The significant increase in gsi of Xinnong 518 did not significantly affect its induction time,indicating the induction time was not limited by gsi.The time to reach 50%of full induction was decreased with the increased of gsi,but when gsi increased to 0.20 mol m-2s-1,the induction time is no longer limited.Terefore,increasing gsi is a simpler route to increasing dynamic photosynthesis,we can enhance the water supply in cultivation.5.During a series of lightflecks,the leaf nitrogen content and gs were coordinated with each other to control the LUE of all cultivars.During stem-elongating stage,the LUE of Xinnong 518 and Yangmai 16 were related to gs under C+T treatment and CT+treatment.At the heading stage,the LUE of XN518 was not affected by gs and nitrogen content under C+T treatment.At grain-filling stage,the LUE of all cultivars were mainly limited by the leaf nitrogen content under CT+treatment and C+T+treatment.This study clarified the reason why CO2 enrichment and temperature increase prolonged the induction time of all wheat cultivars before heading was due to the down-regulation of stomatal conductance,while shortening the induction time after heading was to improve the stomatal conductance.The decrease of lightfleck use efficiency before heading was due to the decrease of stomatal conductance,while the decrease after heading was due to the reduction of leaf nitrogen content. |
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