Effects Of Exogenous Melatonin On Physiological Characteristics And Yield Of Soybean Seedlings Under Drought Stress

In order to study the effect of exogenous melatonin on soybean physiological characteristics and yield under drought stress at soybean seedling stage,and it is expected to provide theoretical basis and technical guidance for soybean drought resistance production.This experiment was carried out in the potted plant of Heilongjiang Bayi Agricultural University in 2018 and 2019."Sui Nong 26" was used as the test material and the potted test method was used.In order to study the regulation function of exogenous melatonin under drought stress on seedling growth of soybean,the drought stress was induced by PEG6000 water osmotic potential（D）,and the melatonin was treated by foliar spraying（LM）and root irrigation（RM）.The effects of exogenous melatonin on soybean morphological characteristics,photosynthesis,antioxidant capacity,osmotic regulation,nutrient uptake and utilization and final yield under drought stress were studied at the soybean seeding stage of V2 and V4.The results are as follows:Melatonin treatment improved the photosynthetic capacity of soybean leaves under drought stress,increased the plant height and leaf area of soybean under drought stress,plant fresh weight and dry matter accumulation.And the total dry weight increased by 13.44%⁵3.34%,and the leaf area increased by 17.72%³1.19%.Among the melatonin treatments,RM had the best treatment effect.Melatonin treatment further increased the antioxidant enzyme activity,antioxidant content and osmotic adjustment content of soybean leaves under drought stress,cleared excess active oxygen,and alleviated oxidative damage in soybean,of which As A content increased from 17.25% to 21.62%,the free proline increased by 3.88% to 55.71%.O₂^-content decreased by 14.33%⁵1.19%,H2O2 content decreased by 17.86%⁵8.36%,and MDA content decreased by 6.57%²9.19%.Among melatonin treatments,RM treatment was the most effective.Melatonin treatment promoted the absorption and utilization of nutrients by soybean under drought stress,increased the content of N,P and K in soybean leaves and stems,and increased the yield components of soybean under drought stress and its yield per plant.Of which the growth rate of soybean yield per plant in 2019 is larger than that in 2018,with an increase of 27.77%⁴5.45%.In addition,soybean yield per plant was the highest under RM treatment.In summary,under the drought stress induced by PEG,through the regulation of exogenous melatonin,the photosynthesis of soybean seedlings is improved,the antioxidant capacity and osmotic adjustment capacity of soybean are enhanced,and the content of ROS and MDA as well as the relative conductivity were reduced,which alleviates oxidative damage,promotes the absorption and utilization of nitrogen,phosphorus,and potassium nutrients by soybean,ensures the growth and development of soybean,and ultimately improves the yield per plant under drought stress.Among them,RM treatment is superior to LM.In the actual production process,melatonin can be used to increase the leaf area of soybeans under drought stress,thereby improving the photosynthesis effect of the group,promoting the synthesis and accumulation of carbohydrates,and providing an early basis for the increase in yield under drought stress.