Effects Of Water Deficit And CO₂ Concentration On Gas Exchange And Water Use Efficiency Of Winter Wheat

Since the Industrial Revolution in the 19th century,the concentration of greenhouse gases（CO₂,N₂O,CH₄,etc）in the atmosphere has increased rapidly,especially the global atmospheric CO₂ concentration（[CO₂]）levels have significantly increased from the industrial revolution of 280μmol mol^-1 to the present level of nearly 400μmol mol^-1,and may even reach about 730～1000μmol mol^-1 at the end of this century.These changes are mainly due to a series of human activities such as the burning large amounts of fossil fuels,cutting down primary forests,and changing land use methods.However,our country relies mainly on agriculture water,but the water resources are in short supply.Therefore,the use of water control mechanisms to improve soil WUE is of great significance to saving water resources.In the past,studies on the effects of CO₂ concentration doubling or different water deficit conditions on winter wheat have been relatively mature,but there are few comprehensive analysis of its multiple factors and the analysis of the correlation between the factors.However,due to the diversity of climate change,the environmental fators are complicated,so we should focus on the influence of multi-factor interaction on the surface stomatal characteristics,photosynthetic performance and WUE of winter wheat leaves.The experiment was conducted in each of eight identical controlled growth chambers,which in full irrigation and regulated deficit irrigation on the basis of the set of two different CO₂ concentration(400μmol mol^-1 and 800μmol mol^-1)to the cultivation of winter wheat under different water deficit conditions to investigate the response of leaf structure,physiological and biochemical processes and WUE of winter wheat to atmospheric CO₂ concentration rise under different water conditions.This study draws the following conclusions:（1）The stomata density of winter wheat leaves increased significantly when the slight water deficit.The carbon dioxide concentration doubled when fully irrigated,significantly increasing the stomata opening and stomata density on the paraxial surface of winter wheat.However,the stomata density and stomata opening of the abaxial and adaxial surfaces of winter wheat show a decreasing trend by improved CO₂concentration under the deficient water.（2）The combined increase of CO₂ concentration makes the spatial distribution pattern of stomatal space in the adaxial side of winter wheat leaves more regular under the condition of full irrigation.However,increasing the concentration of CO₂ results in a more regular distribution of stomata on the abaxial and abaxial surfaces of the blade in a smaller spatial scale under the slight water deficit.（3）The near photosynthetic rate of winter wheat decreased significantly under water deficit.In mild water deficit,the increase in CO₂ concentration increases the net photosynthetic rate,however,it does not reach a significant level.Increasing the concentration of CO₂ leads to a decrease in the net photosynthetic rate under moderate water deficit and severe water deficit.Moreover,the leaf water use efficiency decreased with the increase of water deficit,while the increase of CO₂ concentration did not improve the WUE of winter wheat leaves.（4）Fully irrigated under mild and moderate water deficit conditions,high CO₂concentration significantly reduced winter wheat root soluble sugar concentration and total non-structural carbon content,while increasing CO₂ concentration during severe water deficit increased winter wheat root soluble sugar and Total non-structural carbon content.Under the condition of full irrigation,the concentration of CO₂ increases,which significantly reduces the starch content.Under water deficit conditions,the doubled CO₂ concentration caused the sucrose concentration,soluble sugar content and non-structural carbon content of winter wheat leaves to increase.In addition,under different water conditions,increasing the concentration of CO₂ increased the C%and N%of winter wheat tissues,and at the same time increased the C/N of the winter wheat root system,resulting in a decrease in the C/N of winter wheat leaves.（5）Under different water conditions,the chloroplast content increased the chlorophyll content of winter wheat by increasing the CO₂ concentration.Moreover,it significantly increased by 40.8%and 69.3%in mild and severe water deficits,respectively.It shows that e[CO₂]can alleviate the effect of water stress on the chlorophyll content of winter wheat.In addition,e[CO₂]significantly increased the aboveground biomass,underground biomass,and total biomass of winter wheat by33.8%,99.5%,and 48.0%under sufficient irrigation conditions,while the increase in CO₂ concentration increased the underground biomass of winter wheat under mild water deficit.When the water deficit is moderate,increasing the concentration of CO₂leads to an increase in above-ground biomass.（6）The stomata densities on the abaxial and adaxial surfaces are positively correlated with WUE.At the same time,leaf photosynthesis increased linearly with the increase of stomata length and stomata circumference on both the abaxial and adaxial surfaces.The increase of the stomatal shape index near the seed surface resulted in a linear decrease in leaf photosynthesis.In addition,the linear correlation between the stomata density on the paraxial plane and the net photosynthetic rate of leaves is higher than that on the far axis plane.In addition,the net photosynthetic rate of leaves is positively correlated with stomatal conductance,total biomass and WUE.But there is a negative correlation with non-structural carbon content.