Physiological Response Of Rye Seedlings Under Drought And Freeze-Thaw

Affected by global warming,precipitation in Northeast China has decreased in recent years,and drought stress has frequently occurred.Plant growth is often faced with the effects of drought and low temperature freeze-thaw stress during the green-up period in spring.Ryegrass(Secale cereale L.),Dongmu-70 was used as experimental materials in this paper,and PEG-6000 solutions with concentrations of5%,10%,and 15%g·L~-11 was used to simulate different degrees of drought stress(D1,D2,D3),and high and low temperature alternating test chamber was used to artificially simulate low temperature freeze-thaw stress(FT:10,5,0,-5,0,5,10?)in the lab.Non-photosynthetic physiological characteristics of ryegrass seedling leaves(relative water content,propylene glycol(MDA),soluble sugar(SS),soluble protein,proline(Pro),chlorophyll(Chl),superoxide dismutase(SOD),peroxidase activity(POD)),photosynthetic physiological characteristics(net photosynthetic rate(Pn),transpiration rate(Tr),intercellular CO2 concentration(Ci),stomatal conductance(Gs),water use efficiency(WUE))and the relationship between indicators were studied.The adaptability characteristics of Dongmu-70 ryegrass seedlings under different levels of drought and freeze-thaw stress provide a theoretical basis for the cultivation of Dongmu-70 rye in northern regions.The experimental results showed that:Studies on the changes of non-photosynthetic physiological characteristics of Dongmu-70 seedlings showed that:the content of RWC and Chl decreased,the content of MDA and osmotic substance accumulated,SOD and POD activities increased under drought stress.With the aggravation of drought,the effects of stress on ryegrass leaves increased.Under freeze-thaw stress and combined stress,the RWC and Chl of ryegrass seedlings decreased,and the minimum values appeared at-5°C.The MDA,SS,soluble protein,proline content,SOD and POD activities in ryegrass seedling increased first and then decreased slowly with the change of temperature.The content of SS and POD activity reached the maximum value at 0°C(T5)under combined stress.The seedlings suffered the most damage at-5?~0?,the combined stress of mild or severe drought and freeze-thaw(FD1)was more harmful than that of moderate drought and freeze-thaw(FD2),as was that of severe drought and freeze-thaw(FD3).The damage of stress to the leaves of Dongmu-70 seedlings was roughly as follows:the combined stress group>freeze-thaw group>drought stress group.Studies on photosynthetic physiological responses of Dongmu-70 seedlings showed that:under different degrees of drought,freeze-thaw,and combined stress,the leaves of seedlings were restricted by stomatal,Pn,Tr,Gs,WUE showed a trend of decrease,and Ci increased.The photosynthesis of ryegrass seedlings showed a change pattern as:the combined stress group>freeze-thaw group>drought stress group>control group.With the aggravation of drought stress degree(D1,D2,and D3),the greater the decline in Pn,Tr,Gs,and WUE of seedling leaves,and the more significant the increase in Ci.Combined stress aggravated the damage to the photosynthesis of ryegrass seedlings.It suggested that drought and freeze-thaw stress will cause damage to leaf stomatal structure and weaken photosynthesis.Correlation analysis showed that Ci was negatively correlated with Pn,Tr,Gs,and WUE in the leaves under combined stress,and Tr was significantly correlated with Gs and WUE(P<0.05).Drought and freeze-thaw stress had a synergistic effect on ryegrass,and the aggravation of stress could cause irreversible damage to plants.It showed that the combined damage to plants in the spring-winter alternate season was more harmful than single stress,and proper water control would alleviate the effects of freeze-thaw stress on plant growth.