Alleviation Effect Of Uniconazole On Carbon Metabolism And Yield Of Soybean Under Waterlogging Stress At Initial Flowering Stage

Soybean is an important food crop and economic crop in China,which is very sensitive to water conditions.waterlogging stress is one of the main abiotic stresses that reduce soybean production.Uniconazole（S3307）can resist abiotic stress.The purpose of this study was to explore the effects of waterlogging stress at early flowering stage（R1 stage）on the growth and development,physiological and biochemical characteristics and yield of soybean and the mitigation effect of S3307.This study was carried out in the National miscellaneous Cereals Engineering and Technology Research Center of Heilongjiang Bayi Agricultural Reclamation University from 2019 to 2020.Two soybean varieties with different waterlogging tolerance（waterlogging tolerant variety Kenfeng 14 and waterlogging sensitive variety Kenfeng 16）were used as experimental materials to carry out pot experiment.S3307(50mg·L^-1,225 L·hm^-2)was sprayed on leaves at R1 stage,and waterlogging stress treatment was carried out 5 days after spraying.The morphological,physiological and biochemical indexes,yield and yield components of soybean in R1 stage were measured and analyzed,and the effects of waterlogging stress on growth and development and the mitigation effect of S3307 were studied.The main results and conclusions are as follows.Waterlogging stress in stage R1 inhibited the growth of two soybean varieties,and the plant height,leaf area and aboveground dry matter accumulation decreased significantly with the extension of stress time.After foliar spraying S3307,the plant height of two varieties of soybean was further reduced,the decrease of dry matter accumulation under waterlogging stress was effectively alleviated,the stem diameter of two varieties of soybean was increased,and the lodging resistance was enhanced.After returning to normal water,the above indexes of waterlogging stress treatment（W）recovered,but it was difficult to reach the normal level,while S3307 treatment could accelerate the recovery ability of two soybean varieties and alleviate the damage caused by waterlogging stress.Waterlogging stress at R1 stage significantly decreased photosynthetic pigment content,net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂concentration in two soybean varieties,while water use efficiency and stomatal limit values increased significantly with the prolongation of stress time,thus inhibiting the accumulation of sucrose,fructose and starch content.Foliar spraying of S3307 effectively alleviated the degradation of photosynthetic pigments in soybean leaves under waterlogging stress in stage R1,increased photosynthetic parameters and carbohydrate content,and maintained a high level after returning to normal water management,promoting the normal growth and development of plants.and the recovery ability of Kenfeng 14 is stronger than that of Kenfeng 16.Waterlogging stress in R1 stage led to the destruction of（ROS）metabolic balance of reactive oxygen species in soybean leaves,the rapid accumulation of and H₂O₂content,and then accelerated the process of membrane peroxidation,resulting in a significant increase in MDA content and relative electrical conductivity with the prolongation of stress time.At R1+8,the activities of key enzymes（APX,GR,MDHAR and DHAR）and the contents of non-enzymatic antioxidants（As A,DHA,GSH and GSSG）in the enzymatic antioxidant defense system（SOD,POD and CAT）,ascorbate-glutathione（As A-GSH）cycle were increased to adapt to waterlogging stress,and decreased with the prolongation of stress time.Foliar spraying of S3307 effectively increased the activities of SOD,POD,CAT and APX,GR,MDHAR and DHAR in the leaves of the two soybean varieties,increased the contents of non-enzymatic antioxidants and osmotic substances,effectively inhibited the increase of electrical conductivity,MDA,H₂O₂content andproduction rate,and maintained high enzyme activity and non-enzymatic antioxidant content after returning to normal water treatment.Non-target metabolomics research based on liquid mass spectrometry technology,1274metabolites were screened from the W-CK group,and 1213 metabolites were screened from the WS-W treatment group.After Log₂processing the detected metabolites,the most significant changes in the two groups of metabolites were lipids and lipid molecules.According to the KEGG enrichment analysis,the metabolic pathways that were significantly changed in the W-CK group were flavonoid biosynthesis,tricarboxylic acid cycle,etc.The metabolic pathways in the WS-W group that were significantly changed were arachidonic acid metabolism,valine leucine and isoleucine biosynthesis.It shows that waterlogging stress causes the respiratory rate to be blocked,inhibits the tricarboxylic acid cycle,and improves the ability of soybeans to resist adversity stress by promoting flavonoid biosynthesis.S3307 enhances the stability of cell membranes by improving the metabolic pathway of arachidonic acid.Adapt to the waterlogging environment by increasing the metabolism of unsaturated fatty acids.The number of pods per plant,number of grains per plant,100 seed weight and yield of soybean were significantly decreased under R1 flooding stress,and the decrease was gradually increased with the extension of stress time.Among them,the yield reduction rates of Kenfeng 14and Kenfeng 16 were 5.42%-16.23%and 16.65%-25.15%,respectively.The results showed that S3307 could effectively alleviate the decrease of soybean yield.The stop loss rates of Kenfeng 14 and Kenfeng 16 were 4.76%-4.86%and 23.94%-26.61%,respectively.In conclusion,flooding stress inhibited the normal growth and development of two soybean varieties,and foliar spraying S3307 could alleviate the damage caused by R1 flooding stress.S3307 treatment can ensure the normal photosynthesis of plants by increasing the content of photosynthetic pigment and enhancing the photosynthetic capacity.At the same time,it can induce the activity of antioxidant enzymes,increase the content of non enzyme antioxidants and osmotic adjustment substances,inhibit the accumulation of reactive oxygen species and membrane peroxidation,alleviate the yield reduction caused by flooding stress,and enhance the waterlogging tolerance of plants.