Effects Of Free Air CO₂ Enrichment And Increased Temperature On Photosynthesis Of Different Leaf Position In Wheat

Climate change is mainly characterized by atmospheric CO2 concentration elevation and temperature increase,which strongly affects crop growth.Leaves are important photosynthetic organs of crops.The photosynthetic characteristics of leaves at different leaf positions directly affect the canopy photosynthetic rate of crops,ultimately affecting crop yields.Wheat is one of the most important food crops in the world.Therefore,to lay the foundation for the further establishment of a wheat growth simulation suitable for assessing the impact of future climate change on yield,it is necessary to quantify the effect of elevated CO2 concentration and increased temperature on photosynthetic characteristics of wheat canopy leaves in different positions.In this study,the medium-gluten wheat,Yangmai 14,was used as the experimental material.We designed four experimental treatments,that is,one with target atmospheric CO2 up to 500 μmolmol-1(C+T),one with warming of canopy temperature by 1.5-2.0 ℃ above ambient(CT+),and one with combined CO2 enrichment and warming(C+T+),and taking an untreated plot with ambient condition as control(CT),to analyse the effect of elevated CO2 and increased temperature on photosynthetic characteristics of different leaf positions of wheat canopy in FACE system established in Kangbo village(31°30’N,120°33’E),Guli Township,Changshu Municipality,Jiangsu,China during 2017.Using field observation data,we quantitatively analyzed the effects of elevated atmospheric CO2 concentration and increased temperature on photosynthetic parameters of different leaf positions of wheat(light-saturated net photosynthetic rate Anmax,day respiration rate Rd and initial quantum efficiency of photosynthesis ε)and the cause of this effect(stomatal conductance gs,intercellular CO2 concentration Ci,ratio of intercellular CO2 concentration to atmospheric CO2 concentration Ci/Ca,leaf nitrogen content).The main research results were as follows:1.Elevated CO2 and increased temperature increased light-saturated net photosynthetic rate Ag,max of each leaf position at the jointing and heading stages,but it decreased Ag,max of functional leaves at the milking stage.At the jointing and heading stages,the C+T treatment increased Ag,max of flag leave、the second top leave and the third top leave by 24.2%、13.6%and 14.9%,and there were significant different in flag leave between control and the treatment;The CT+treatment increased Ag,max of flag leave,the second top leave and the third top leave by 11.6%、26.3%和 49.1%,showing an increase with the leaf position(from the top to the bottom of the plant);and there were significant different in flag leave between control and the treatment at the jointing stage;The C+T+treatment significant increased Ag,max of each leaf position.At the milking stage,the C+T treatment reduced Ag,max of flag leave,and the difference was not significant between control and the treatment.The CT+and C+T+treatment significant reduced Ag,max of flag leave.2.Elevated CO2 and increased temperature had no significant effect on the initial quantum efficiency of photosynthesis ε of each leaf position at the jointing and heading stages,but it significant increased day respiration rate Rd of the third top leave at the heading stage.Elevated CO2 and increased temperature significant decreased ε of functional leaves at the milking stage.At the jointing and heading stages,the C+T treatment had no significant effect on the Rd and ε of leaves at each leaf position;the CT+treatment and C+T+treatment significantly increased Rd of the third top leave at the heading stage.At the milking stage,the C+T and C+T+treatment significantly reduced ε.3.Elevated CO2 concentration significantly reduced the stomatal conductance of flag leave in the jointing stage of winter wheat,and it had little effect on the stomatal conductance at the heading and milking stages.This indicated that the stomatal conductance of the leaves at the reproductive stage of the winter wheat,which produced adaptability to the increase of CO2 concentration.4.Under the condition of elevated CO2 and increased temperature,Ag,max and Rd were still linearly related to the leaf nitrogen content.The elevated CO2 and increased temperature caused the decline of nitrogen content of the leaves during the reproductive growth period,which leads to the reduction of Ag,max of leaves in different positions of winter wheat.This study identified the effects of elevated CO2 concentration and increased temperature on photosynthetic characteristics of different leaf positions of winter wheat.And this work set scientific concsultation and theoretical basis for futher studying the effect on winter wheat which caused by global climate change.