Effects Of Drought Stress On Physiological And Photosynthetic Characteristics Of Soybean

Soybean（Glycine max L.Merr.）is the most important food and oil crops in China,which contains abundant proteins and fatty acids necessary for human body.Drought is an important limiting factor for soybean growth and yield formation,and water shortage is also a major problem of irrigation water in China.This experiment was carried out in the glass shed of Northeast Agricultural University from 2020 to 2021,with drought-resistant soybean variety HN44 and sensitive soybean variety HN65 as experimental materials.The effects of stage drought and local irrigation on physiological and photosynthetic characteristics of soybean were further researched,for clarified the response characteristics of soybean growth,protective enzyme activity,osmotic adjustment substances,membrane lipid peroxidation,metabolic level and yield to phased drought.And the regulatory effects of localized irrigation on soybean growth,antioxidant characteristics and photosynthetic characteristics were also studied,which provided theoretical basis and practical experience for drought-resistant cultivation and water-saving irrigation of soybean.The main results are as follows:（1）Drought stress reduced dry matter accumulation in leaves,stems and pods of HN44 and HN65,and the higher the drought stress,the lower the dry matter accumulation.The dry matter accumulation of leaves,stems and pods of HN44 decreased most significantly when drought stress occurred at R₁,R₃ and R₅,respectively.The dry matter accumulation of leaves,stems and pods of HN44 decreased by 85.6%,74.7%and 94.7%,respectively.The dry matter accumulation of leaves,stems and pods of HN65 fell by 113.4%,90.5%and 115.0%respectively.Drought led to the decrease of 100-seeds weight of the two varieties.The higher the drought stress level,the lower the 100-seeds weight and yield.In the R₅ stage,the effect was greater than other periods,the 100-seeds weight and yield of HN44 decreased by 63.9%and 69.7%,the 100-seeds weight and yield of HN65decreased by 87.5%and 123.7%,respectively.The 100-seeds weight and yield of HN44 decreased lower than HN65.（2）Drought stress increased the activities of superoxide dismutase（SOD）,catalase（CAT）and ascorbate peroxidase（APX）in leaves of HN44 and HN65,and the sensitivity degree of different protective enzymes was different at different stages.The SOD activity showed a single peak curve with the aggravation of drought stress and the activity was the highest under moderate stress.The SOD activity of HN44 and HN65 increased by 188.2%and 179.0%respectively compared with the control.The CAT and APX activities were the highest under moderate and severe stress treatments respectively.The CAT activities of HN44 and HN65 increased by 237.1%and 234.7%compared with the control,respectively;the APX activities of HN44 and HN65 increased by 611.2%and 538.7%compared with the control,respectively.The SOD and CAT activities of the two varieties were the highest at R₃ stage,and the APX activity was the highest at R₅ stage.The protective enzyme activity of HN44 and its increase rate under drought conditions were higher than HN65.（3）Drought stress increased the contents of soluble sugar,soluble protein and proline in leaves of HN44 and HN65,which increased with the intensiation of drought stress.Soluble sugar content of HN44 and HN65 increased by 26.8%and 23.0%,soluble protein content increased by 49.8%and49.1%,proline content increased by 1599.5%and 1198.2%,respectively.Under drought conditions,the content of soluble sugar in HN44 was the highest at R₅ stage,the content of soluble protein and proline was the highest at R₃ stage,the content of soluble sugar and proline in HN65 was the highest at R₅ stage,and the content of soluble protein was the highest at R₁.The content and increase of osmotic adjustment substances in HN44 were higher than those in HN65.Drought stress increased the MDA content in leaves of HN44 and HN65,and increased with the aggravation of drought stress.Compared with the control,HN44 and HN65 increased by 148.3%and 192.5%,respectively.Under drought conditions,HN44 had the highest content in R₁ and HN65 had the highest content in R₅.The MDA content and increase of HN65 were higher than HN44.（4）The relative chlorophyll content（SPAD）,primary light conversion efficiency（Fv/Fm）,potential photochemical efficiency（Fv/F₀）and apparent electron transfer efficiency（ETR）of HN44and HN65 were decreased by drought stress.The quantum yield of non-regulatory energy dissipation（Phi NO）,quantum yield of regulatory energy dissipation（Phi NPQ）and non-photochemical quenching coefficient（NPQ）increased,and the actual photosynthetic efficiency（Phi2）increased first and then decreased.Drought stress significantly affected chlorophyll synthesis,destroyed photosynthetic structure,and reduced photosynthetic efficiency.The longer the stress time,the more significant the effect.HN44 was less affected than HN65.（5）In metabolomics,OPLS-DA model was used to screen different metabolites.101 differential metabolites were found in HN44（49 up-regulated and 52 down-regulated）;120 differential metabolites were found in HN65（45 up-regulated,75 down-regulated）.KEGG analysis showed that the drought resistance pathways of HN44 and HN65 were different.Amino acid metabolism and lipid metabolism played key roles in drought resistance of the two cultivars respectively.The tricarboxylic acid cycle（TCA）is one of the core pathways of drought resistance of the two cultivars.The variation of L-aspartic acid and citric acid content was one of the reasons for the difference of drought resistance between the two cultivars.Secondary metabolites such as phenolic acids,flavonoids,alkaloids,terpenoids and organic acids also play an important role in drought resistance of soybean.（6）Under local irrigation,the accumulation rate of dry matter in leaves,stems and roots of HN44 and HN65 was higher than that in all drought conditions,the activities of SOD,CAT and APX and the contents of soluble sugar,soluble protein and proline were also increased,while the content of MDA and its increase range were lower than that in all drought conditions.The decrease of SPAD,Fv/Fm,Fv/F₀ and ETR was less than that of all droughts,and the increase of Phi NO was less than that of all droughts.Phi NPQ,NPQ and Phi2 also changed to some extent.Under local irrigation,the two cultivars had strong ability to remove reactive oxygen species and protect photosynthetic system.But when the stress time is too long,it will still cause great harm to the growth and development of soybean plant.However,when the stress time is too long,it will still cause great damage to the growth and development of soybean plants.HN44 suffered less damage than HN65.