Effects Of Water Deficit On Growth,Stomatal Traits And Of Physiological And Biochemical Processes Of Green Peppers Under Doubling CO₂ Concentrations

Since the industrial revolution in the 19th century,the atmospheric CO₂concentration has increased dramatically.Meanwhile,the increase of atmospheric CO₂concentration aggravates climate warming through greenhouse effect,and further changes the global rainfall pattern,thus affecting the global water distribution balance,resulting in uneven seasonal precipitation distribution and frequent regional drought events,resulting in a sharp decrease of available water for crops,especially the agricultural grain production in North China Plain is facing a more severe water shortage problem.Therefore,the growth and development of green pepper plants will inevitably be affected by water deficit,which will become one of the important factors limiting the yield of green pepper plants.However,in the past,most studies only focused on the single factor of CO₂ concentration or water deficit,and there were few reports on the mechanism of synergistic effects of CO₂ concentration doubling and water deficit on physiological and biochemical characteristics of green pepper plants.Even the mechanism of CO₂ concentration and water deficit on green pepper growth has not reached a consistent conclusion.Therefore,in this study,eight large-scale artificial climate chambers which can accurately control CO₂ concentration were set with two different CO₂ concentrations(400μmol mol^-1 and 800μmol mol^-1)and four different water gradients（75–85%FC,full irrigation;65–75%FC,mild water stress;55–65%FC,moderate water stress;45–55%FC,severe water stress;FC is the field water holding capacity）for 90 days,and the effects of water stress on plant growth,stomatal characteristics and physiological and biochemical processes of green pepper plants were discussed.The main conclusions are as follows:（1）When green pepper plants were in the early anthesis stage,the stomatal density on the adaxial surface was significantly increased by water deficit under the condition of doubling atmospheric CO₂ concentration,and the stomatal density on the abaxial surface was significantly increased by 107.9%under severe water stress.When green pepper plants were in the anthesis stage,under mild water stress,atmospheric CO₂concentration doubled to increase the stomatal density of adaxial surface and abaxial surface by 65.1%and 79.1%,respectively.When green pepper plants were in the maturation stage,under the condition that the atmospheric CO₂ concentration doubled,the stomatal density on the adaxial surface of leaves decreased by 35.2%,23.5%and21.0%,respectively.However,it had no significant effect on the stomatal density on the abaxial surface.（2）When green pepper plants were in the early anthesis stage,the stomatal area on the abaxial of leaves increased by 74.6%,39.2%and 46.0%,respectively,and the length,perimeter and area of the adaxial of leaves increased significantly under mild water stress.When green pepper plants were in the anthesis stage,under the condition of doubling atmospheric CO₂ concentration,water deficit had no significant effect on the width of stomata on the adaxial surface,while severe water stress significantly increased the length and circumference of stomata on the abaxial surface by 14.1%and13.0%.When green pepper plants were in the maturation stage,the width,perimeter,area and shape index of stomata on the abaxial surface were significantly increased by mild water stress when the atmospheric CO₂ concentration doubled.（3）When green pepper plants were in the early anthesis stage,the doubling of CO₂concentration led to the decrease of stomatal regularity on the adaxial surface under water stress,while mild and moderate water stress made the distribution of stomatal on the abaxial surface were more regular.When green pepper plants were in the anthesis stage,the doubling of CO₂ concentration led to the decrease of the regularity of adaxial stomata under mild and severe water stress,while the stomata were distributed more regularly under mild water stress.When green pepper plants were in the maturation stage,the doubling of CO₂ concentration led to the decrease of the regular degree of stomata in the adaxial plane under moderate water stress,while the regular degree of stomata in the abaxial plane decreased under mild and severe water stress.（4）Under mild,moderate and severe water stress,the content of soluble sugar in green pepper leaves increased by 17.9%,39.5%and 57.9%respectively.Compared with soluble sugar,the doubled CO₂ concentration significantly affected the starch and TNC contents in leaves under full irrigation and severe water stress,and the starch and TNC contents decreased significantly under full irrigation,but increased significantly under severe water stress.In case of doubling CO₂ concentration,the content of C and N in green pepper leaves generally decreased due to water stress.However,moderate and severe water stress significantly increased C/N of leaves compared with full irrigation.（5）The net photosynthetic rate（P_n）increased by 38.9%by doubling CO₂concentration under full irrigation.Meanwhile,the doubling of CO₂ concentration significantly increased P_n by 14.7%,25.2%and 15.6%under water stress,respectively.Under full irrigation,moderate and severe water stress,the water use efficiency（WUE）of leaves increased by 95%,100%and 56%,respectively.（6）Under full irrigation,mild and moderate water stress,the doubling of CO₂concentration increased the total biomass of green pepper plants by 35%,54%and130%,respectively.In addition,under the conditions of full irrigation and mild water stress,the doubled CO₂ concentration increased the aboveground biomass by 48%and42%respectively,and the underground biomass nearly doubled.Under CO₂concentration doubling and severe water stress,the total biomass,aboveground biomass and underground biomass of green pepper plants had almost no change.