Physiological Responses Of Highland Barley Seedlings To Freeze-thaw And Saline-alkali Stress With Addition Of Artemisinin And Potassium Fulvic Acid

In Qinghai-Tibet plateau,alternating freeze-thaw phenomenon occurs frequently,meanwhile,due to low rainfall and high evaporation,soil salinization is common.Therefore,crops are commonly subjected to freeze-thaw and saline-alkali stress simultaneously in Tibetan areas.In addition to two kinds of stresses above,allelopathy is also a non-negligible ecological stress factor,which restricts crop growth.Artemisia annua L.,a field weed widely distributed in Southwest China,can release artemisinin,which affect the growth of crops.Moreover,the organic compound potassium fulvic acid,used as a fertilizer in agriculture,can enhance the stress resistance of plants and farmland ecosystem.In this study,highland barley（H.vulgare L.）,the most important crop in Tibetan region,was used as the experiment material,along with the addition of artemisinin and potassium fulvic acid,the combined stress and mitigation mechanism under freeze-thaw conditions were studied,which illustrated the physiological response mechanism of barley seedlings.The highland barley variety used in this study was Beiqing-3.In order to investigate the alleviating effect of artemisinin on combined stresses of freeze-thaw and salt,through indoor hydroponic experiment,150 mmol/L sodium chloride solution and 20 mg/L artemisinin solution were applied to treat highland barley seedlings for 8 d.Subsequently,a freeze-thaw treatment was carried out.The changes of osmotic substances,superoxide dismutase（SOD）activity and photosynthetic characteristics of barley seedlings in different treatment groups were explored.The results showed as follows.Under salt stress,soluble protein content and relative water content（RWC）of barley seedlings decreased,relative conductivity,soluble sugar,malondialdehyde（MDA）content and SOD activity increased,and photosynthetic rate decreased.After freeze-thaw treatment,soluble protein content of seedlings increased,and protein content in combined stresses of artemisinin,salt and freeze-thaw（FAS）increased by 97.8%,with the largest increase.The relative conductivity of FAS group was significantly lower than that of combined stresses of salt and freeze-thaw（FS）（P<0.05）.The content of MDA and soluble sugar in FAS group was lower than that in FS group,while SOD activity in combined stresses of artemisinin and freeze-thaw（FA）and FAS group decreased.Photosynthesis in all freeze-thaw groups was weakened,and intercellular CO₂ concentration（Ci）in FAS group was significantly lower than that in single freeze-thaw stress（F）,FA and FS groups（P<0.05）.Compared with the control group without artemisinin,the addition of artemisinin could alleviate the damage of salt and freeze-thaw stress on barley seedlings.In order to explore the alleviating effect of potassium fulvic acid on combined stress of freeze-thaw and alkaline salt,60 mmol/L sodium bicarbonate solution and0.5 g/L potassium fulvic acid solution were applied to treat highland barley seedlings for 8 d.Subsequently,a freeze-thaw treatment was carried out.The changes of osmotic regulation substances,SOD activity,peroxidase（POD）activity and photosynthetic characteristics of barley seedlings under different treatments were investigated.The results showed as follows.Under alkaline salt stress,the soluble protein and MDA content of barley seedlings increased significantly（P<0.05）,and MDA content increased by 63.1%compared with control group（CK）,while SOD activity,POD activity and photosynthetic rate decreased.After freeze-thaw treatment,the soluble protein content of barley seedlings decreased,and the protein content of combined stresses of alkaline salt,potassium fulvic acid and freeze-thaw（FHK）was significantly higher than that of other freeze-thaw groups（P<0.05）,the relative conductivity and MDA content of FHK group were significantly lower than that of combined stresses of alkaline salt and freeze-thaw（FH）（P<0.05）,and the enzyme activity of FHK group was higher than that of FH group.Net photosynthetic rate decreased in each group.Compared with the control group without potassium fulvic acid,the addition of potassium fulvic acid could mitigate the damage of alkaline salt and freeze-thaw stress on barley seedlings.Both saline-alkali and freeze-thaw stress had significant physiological damage on barley seedlings,and the combined stresses had a superimposed effect,but the addition of tiny amounts of artemisinin and potassium fulvic acid weakened this effect.The results showed that the appropriate amount of artemisinin and potassium fulvic acid could improve the tolerance of highland barley to freezing and saline-alkali stress under short-term combined stresses of freeze-thaw and salinity,which is expected to provide some theoretical references for scientific cultivation and management of highland barley.