Physiological Mechanism Of Exogenous Silicon Alleviating Drought Stress In Maize

With the global warming,the impact of drought on agricultural production is increasingly prominent.Maize,one of the most widely cultivated crops in the world,is an extremely important food,feed and economic crop in China.With the development of my country's national economy and the improvement of people's living standards,there is a gradually increasing demand for maize consumption,which has increased the importance of maize in the development of the national economy.Maize has a long growth period,high water demand,and is more sensitive to drought.Therefore,drought has always been one of the limited factors affecting the stable and increased on global maize production.In recent years,it has been found that silicon(Si)can promote plant growth and enhance plant resistance to multiple stresses.At present,many scholars have shown that Si fertilizers can alleviate the damage caused by drought stress on plants to a certain extent at home and abroad.In addition,most of the planting measures such as hydroponics and potted plants have used to simulate the degree of drought resistance by PEG-6000 to study the effects of Si fertilizer on single growth period or single drought degree treatment of maize.However,there are few studies on the effects of exogenous Si on different growth stages and drought degrees of maize.The jointing stage and the tasseling stage of maize treated with normal water treatment,moderate and severe drought stress.In this experiment,to study its effects of drought in the large farmland moisture control test field(Xianyu 335)combined with exogenous Si on maize growth,relative water content,photosynthetic pigment contents,gas exchange parameters,photosynthetic enzyme activity,reactive oxygen species,membrane damage degree,antioxidant defense system,osmotic regulator,stomatal development characteristics and yield.The purpose is to clarify the mechanism of exogenous Si on maize drought in different growth stages and to provide a theoretical basis for reasonable application of silicon.The main results are as follows:(1)With the intensification of drought stress,the average growth rate and biomass of maize decreased significantly.Compared with the same level of drought stress,spraying of exogenous Si could significantly promote the growth of maize in different growth stages.(2)To a certain extent,exogenous Si alleviated the damage of drought stress on maize photosynthetic system and improved the photosynthetic capacity of plant leaves.Compared with the same level of drought-stressed alone,applying exogenous Si could promote photosynthetic pigment contents,gas exchange parameters,photosynthetic enzyme activity,stomatal length stomatal width,stomatal aperture length and stomatal aperture width in different growth stages of maize,and the increase range is 0.71%?45.19%,0.98%?95.72%,0.74%?37.01%,0.65%?14.30%,0.89%?28.54%,0.74%?17.15%,5.32%?46.17%;decreased the number of stomatal by1.65%?14.44%.(3)The application of exogenous Si could promote the synthesis of osmotic substances in plants under drought stress.Compared with the same level of drought stress,applying exogenous Si significantly increased the content of the relative water content 0.48%?10.29%of maize leaves and further promoted the synthesis of proline,soluble sugar,soluble protein and free amino acid,and the increase range is 0.89%?13.35%,0.73%?21.58%,1.09%?35.93%and 0.57%?18.21%(4)Under drought stress,the superoxide anion(O₂^·-)production rate,hydrogen peroxide(H₂O₂),malondialdehyde(MDA)and electrolyte leakage(EL)increased significantly.The activities of superoxide dismutase(SOD),peroxidase(POD),catalase(CAT),ascorbate peroxidase(APX)and glutathione reductase(GR)increased significantly.The activities of monodehydroascorbate reductase(MDHAR)and dehydroascorbate reductase(DHAR)decreased significantly.In the cyclic metabolism of AsA-GSH,with the degree of drought in jointing stage,AsA increased first and then decreased,GSH increased significantly.With the degree of drought in tasseling stage,AsA decreased significantly and GSH increased significantly.Compared with the same level of drought-stressed alone,applying exogenous Si significantly reduced the production rate of O₂^·-,the contents of H₂O₂,MDA and EL,the reduction range is2.27%?12.43%,0.60%?13.58%,1.85%?25.42%and 1.39%?13.33%;further increased the activity of SOD,POD,CAT,APX and GR,the increase range is 2.31%?18.12%,0.56%?12.83%,4.90%?37.21%,2.10%?41.26%,3.29%?45.46%and increased significantly the contents of MDHAR,DHAR,AsA and GSH,the increase range is 3.14%?40.27%,0.29%?15.91%,0.37%?19.98%,0.93%?21.33%.The levels of oxidized ascorbic acid(DHA)and oxidized glutathione(GSSG)decreased,the reduction range is 1.57%?17.88%and 2.03%?21.89%.(5)With the intensification of drought stress,the yield of maize decreased significantly.Compared with the same level of drought stress,applying exogenous Si can promote the growth of maize root and increase root dry biomass accumulation under drought stress,and finally increase maize yield 1.90%?20.10%.(6)Based on principal component analysis,among the three kinds of exogenous Si,Si-50G has the best treatment effect under drought stress,followed by Si-60G,and finally Si-EG,and the optimal concentration is 15 g·L^-1.The effect of exogenous Si on maize moderate drought stress treatment is better than that of severe drought stress treatment,and the effect of alleviating tasseling stage is better than that of jointing stage.In summary,applying exogenous Si can increase the average growth rate of maize plant height,biomass,photosynthetic pigment contents,gas exchange parameters,photosynthetic enzyme activities,length and width of stomatal,and length and width of stomatal aperture under drought stress,decrease the number of stomatal,thereby enhancing the photosynthesis capacity of plants;promote the synthesis of osmotic substances,thus improving plant water metabolism balance;and enhance the antioxidant system,remove toxic substances,reduce membrane peroxidation,maintain cell membrane stability,alleviate stomatal limitation,and enhance maize drought resistance of the plant,thereby increasing yield.