Physiological Mechanism Of Sorghum Response To Waterlogging Stress And Alleviating Solutions

With global warming,waterlogging has become an important abiotic stress restricting agricultural production.As the fact that the sorghum has strong stress resistance and is often planted in some marginal lands,such as,in low-lying land or land along the beach,it will be easily affected by waterlogging when it encounters short-term and heavy rainfall,which will result in a decline in yield and quality of sorghum.Therefore,studying the response of sorghum to waterlogging stress and exploring its mechanism of great significance for achieving high yield and quality of sorghum.This experiment was carried out in the experimental field of Shenyang Agricultural University from 2017 to 2019,and the waterlogging-resistant variety of Jinuoliang 01(JN01)and waterlogging-sensitive variety of Jinza 31(JZ31)were selected in the study.The waterlogging stress were performed at the five-leaf stage(V5),flowering stage(VF),and milky stage(VM),respectively,and the effects of waterlogging on sorghum yield and quality in different periods were observed.Moreover,we compared the differences in plant morphology,physiology,and transcriptional regulation between the two varieties to explore waterlogging tolerance mechanisms.We studied the effects of different regulated measures on photosynthetic characteristics,active oxygen metabolism,and nitrogen accumulation of sorghum under waterlogging stress to evaluate the mitigated effects of different measures to waterlogging stress.The results are as follows:1.After waterlogging treatment,the yield and quality of sorghum significantly decreased,however,the impact of waterlogging in different periods on yield and quality varies.When the waterlogging occurred during V5,VF and VM,in 2017,the grain yield of JN01 was decreased with 54.58%,21.24%,and 8.63% compared with the control,respectively,and for JZ31 was also decreased with 69.52%,29.30%,and 18.02% compared with the control,respectively;In 2018,the grain yield of JN01 decreased by 52.01% and 18.64% and 5.35%,compared with the control,while decreased by 71.97%,31.74% and 20.91% for JZ31.It indicated that the waterlogging occurred during V5 had the worst impact on sorghum grain yield,followed by the flowering stage,and the waterlogging occurred during VM had the least impact on sorghum grain yield.It was also found that the waterlogging stress could cause significant reductions in crude protein,crude fat,and tannin content in the grain,especially for the waterlogging occurred during V5.Therefore,the V5 is a sensitive period for sorghum waterlogging.2.Waterlogging stress severely restrained the growth of sorghum plant height and leaf area.After the waterlogging stress,the aerenchyma was found in the base of the stem,which provided a transported channel for oxygen to the roots of sorghum.Due to the rhizosphere hypoxia caused by waterlogging stress seriously affects sorghum root growth and development,and also resulted in obvious decrease of root vigor of adventitious root.It found that the new adventitious roots which had lots of aerenchyma and maintained higher root vigor for the new adventitious roots played an important role after waterlogging.Moreover,the number and the average length of the new adventitious root in JN01 were significantly higher than those in JZ31.Therefore,the rapid development of the new adventitious roots of sorghum is one of the waterlogging tolerance mechanisms of sorghum.There were more soluble proteins and soluble sugars in new adventitious roots and had higher activity of pyruvate decarboxylase(PDC)and alcohol dehydrogenase(ADH)which may be an important reason that there were more new adventitious roots for JN01 than JZ31.3.Compared the transcriptome sequencing data of two sorghum varieties with different waterlogging tolerance before and after waterlogging treatment.It showed that differential genes were mainly involved in the pathways of fatty acid degradation,fructose mannose metabolism,glycolysis / gluconeogenesis,amino sugar and nucleotide sugar metabolism,arginine and proline metabolism.These metabolic differences in these pathways may be the reason why sorghum had different numbers of the new adventitious roots after waterlogging,and thus show different waterlogging tolerance.We also found that phosphoglycerol kinase genes,pyruvate decarboxylase genes,alcohol dehydrogenases genes in glycolysis,and prolyl hydroxylase genes in arginine and proline metabolism,auxin transporter genes and auxin response factor genes in the hormone metabolism pathway may be the key genes that determined the differences in sorghum waterlogging tolerance by using the In-depth analysis of differential genes in the main pathways.4.The decline of the root vigor caused by waterlogging stress produce severel effects on the absorption of water and nutrients by root system.Waterlogging stress causes sorghum leaf water content decreased,especially free water content,resulting in thinner leaves and lower specific leaf weight.In addition,the decreased of the leaf water content increased the plant leaf temperature.The temperature difference between leaf and air could be used as an important indicator for charactering sorghum waterlogging stress.It also show that waterlogging stress caused the accumulation of nitrogen,phosphorus,and potassium in sorghum shoot and root significantly decreased.Waterlogging stress significantly decrease the content of nitrogen,phosphorus,and potassium in sorghum shoot and less effect in root.Compared with JN01,the water content and nitrogen,phosphorus and potassium content of JZ31 were more severely affected by waterlogging stress.5.Waterlogging had severely affect on the photosynthesis of sorghum.At the early stage of waterlogging,the obstruction of gas exchange caused by the decrease of leaf stomatal conductance was the main reason for declining photosynthesis.With advanced watrtlogging duration,the active oxygen in sorghum leaves increased,which leaded destruction of the chloroplast structure and photoreaction center,and decline of the chlorophyll content,which ultimately occurred a decrease in sorghum photosynthetic capacity.Compared with watersensitive sorghum JZ31,water-tolerance sorghum JN01 which had the capability of higher nonphotochemical quenching coefficient(NPQ)and higher activity of peroxidase(POD),catalase(CAT),and aseorbateperoxidase(APX)under waterlogging stress.It could effectively maintain high photosynthetic capacity by reducing active oxygen content and alleviating the damage to the photoreaction center.6.Foliar spraying of nitrogen fertilizer and melatonin could alleviate the stress of waterlogging on sorghum,mainly by increasing the antioxidant enzyme activity,the soluble protein and chlorophyll content of leaves,and improving photosynthesis and reducing the accumulation of MDA under waterlogging stress.Moreover,it proved that the combined application of foliar nitrogen fertilizer and melatonin will more superior than the single application.