Effects Of Elevated CO₂ Concentration And Water Deficiency On Stomatal Traits,Leaf Gas Exchange Parameters And Biochemistry Of Maize

Maize（Zea may L.）is a globally planted C₄ crop and also one of the most important grain crops in the North China Plain region of China.To investigate in depth the potential mechanisms by which elevated CO₂ concentration（[CO₂]）and water deficiency synergistically affect the growth development and physiological and biochemical processes of C₄ crops.We grew maize cultivars‘Zhengdan 958’in environmental growth chambers controlling at different CO₂ concentrations(400μmol·mol^-1 and 800μmol·mol^-1)and water supply levels（Full irrigation 75-85%FC,Mild water deficiency 65-75%FC,Moderate water deficiency 55-65%FC,Severe water deficiency,45-55%FC and FC is the field water holding capacity）.Then,we examined the stomatal characteristics,leaf gas exchange parameters,and biochemical properties of maize plants.The main findings are as follows:（1）Under the treatment of ambient CO₂ concentration,soil water deficiency resulted in a significant decrease in stomatal density,stomatal width,stomatal perimeter and stomatal area on the abaxial surface of maize leaves.At the same time,elevated CO₂concentration significantly reduced stomatal density,stomatal length,stomatal perimeter and stomatal area on the adaxial and abaxial surfaces of maize leaves under full irrigation conditions.However,elevated CO₂ concentration resulted in a significant increase of about 20%in stomatal density on the abaxial of maize under mild water deficiency conditions.In addition,the results of this study also showed that the spatial distribution pattern of stomata under mild,moderate and severe water deficiency was more regular in maize than under full irrigation.（2）Compared to adequate irrigation,mild and moderate water deficiency resulted in24.8%and 19.8%decreased net photosynthetic rate（P_n）of maize leaves,respectively,but elevated CO₂ concentration significantly increased P_n of maize leaves by 15.8%and25.7%under mild and moderate water deficiency conditions.In addition,elevated CO₂concentration also led to a significant decrease in transpiration rate（T_r）and stomatal conductance（G_s）of maize under different water deficiency,which substantially increased the instantaneous water use efficiency（WUE_i）at the maize leaves.（3）Soil water deficiency reduced Fv/Fm,Φ_PSII,ETR,and q P in maize leaves.However,elevated CO₂ concentration not only resulted in 34.9%and 18.9%increase in ETR under mild and moderate water deficiency,respectively,but also significantly increased q P by 32%in maize under mild water deficiency.（4）Mild and severe water deficiency resulted in increased soluble sugar content in maize roots and leaves.However,elevated CO₂ concentration increased soluble sugars and nonstructural carbohydrates content of maize leaves under mild and moderate water deficiency conditions.In addition,although mild deficiency and moderate water deficiency reduced maize leaf nitrogen（N）content,elevated CO₂ concentrations resulted in a significant increase in maize leaf N content under both soil water conditions.（5）Soil water deficiency reduced aboveground,belowground and total biomass of maize plants to some extent,while elevated CO₂ concentration significantly increased the aboveground biomass and total biomass of maize under mild water deficiency by 52.2%and 46.4%.Our results suggested that soil water deficiency could limit the plant growth and development of maize,but elevated CO₂ concentration increased the leaf N content,stomatal density on the abaxial leaf and photosynthetic electron transfer rate of maize plants under mild and moderate water deficiency conditions.Therefore,increasing maize plant biomass accumulation as well as leaf carbon assimilation capacity and water use efficiency.Our results may provide a solid theoretical basis and data support for the development of scientific management measures for agricultural ecosystems under the context of global climate change as well as green and efficient quality and yield enhancement of agricultural crops.