Effects Of Heat And Drought Stresses On Leaf Physiological Characteristics,Nutrient Accumulation And Yield Of Maize At Grain Formation Stage

Heat and drought stress are the main abiotic stresses encountered in maize production in Southwest China,which are the main environmental stress factors affecting grain yield.The period of grain formation is the key period of endosperm cell and starch grain formation,and it is also the most sensitive period to adversity.In this study,the effects of heat and drought stresses on photosynthetic characteristics,osmotic regulation and antioxidant defense system,mineral nutrient uptake and yield of maize were studied by pot experiment with control（28°C,80%field capacity）,heat（35°C,80%field capacity）,drought（28°C,50%field capacity）and heat+drought（35°C,50%field capacity）treatments during the grain formation period.The physiological response mechanism of maize to heat,drought and heat+drought stress was analyzed to provide theoretical reference for stress-resistant cultivation of maize in Southwest China.The main results of this study are as follows:1.The chlorophyll content,carotenoid content,relative water content,net photosynthetic rate,transpiration rate,stomatal conductance of maize leaves decreased,and the intercellular CO₂ concentration increased under stress treatments,and the influence degree of heat+drought stress was higher than heat or drought stress.Drought stress had a greater decrease in total chlorophyll content than heat stress,the content of chlorophyll was as follows:control>heat>drought>heat+drought.On the 15th day,net photosynthetic rate of maize leaves decreased by 21.14～25.29%,32.21～34.43%and47.23～48.80%under heat,drought and heat+drought stress,respectively.The total chlorophyll content and net photosynthetic rate of Xida 889 were higher than Xida 319.2.Cell membrane lipid peroxidation was enhanced under stress treatments,and the contents of reactive oxygen species（ROS）and malondialdehyde（MDA）were significantly increased,with the increase of heat+drought>drought>heat.Under stress treatments,soluble protein content in maize leaves decreased,catalase（CAT）and ascorbate peroxidase（APX）activities decreased,while free proline content increased,superoxide dismutase（SOD）,glutathione（GSH）and total antioxidant capacity（AOC）activities significantly increased,and total antioxidant capacity of plants increased.Xida889 maintained higher SOD enzyme activity,GSH,AOC content and higher free proline content than Xida 319,showing higher antioxidant capacity and osmotic regulation ability.3.Heat,drought,heat+drought stress significantly reduced the accumulation of N,P and K in maize roots and stems,and the decrease of heat+drought stress was higher than univariate stress.There was no significant difference in N,P and K accumulation in leaves under heat stress.Drought,heat+drought stress significantly reduced N,P and K accumulation in leaves.The organs of Xida 889 maintained higher accumulation than Xida 319,which was conducive to the normal progress of various physiological activities.4.Stress treatments significantly reduced the number of ears and 1000-grain weight of maize,and reduced the grain yield.Xida 319 decreased by 26.40%,31.99%and 47.57%respectively,Xida 889 decreased by 22.95%,27.23%and 41.66%under heat,drought,heat+drought stress,respectively.Drought,heat+drought stress significantly reduced the dry matter accumulation of maize roots,stems,leaves and shoots,and heat stress significantly reduced the dry matter accumulation of maize roots and shoots.The dry matter accumulation of shoot was as follows:control>heat>drought>heat+drought.In summary,heat,drought and the double stress treatments reduced the photosynthetic pigment content,increased stomatal resistance,and reduced the photosynthetic rate,inhibiting the photosynthesis of leaves,weakening their material production capacity.The accumulation of ROS and MDA increased,and the lipid peroxidation of cell membranes was enhanced,which caused direct damage to the biofilm system and caused metabolic disorders inside cells.Under stress treatment,the number of ears and grain weight decreased,resulting in a decrease in grain yield.The effects of heat+drought stress on photosynthesis,osmotic regulation,accumulation of reactive oxygen species and plant nutrient accumulation of maize were greater than single factor stress.