Studies On Physiological Ecology Characteristics And Drought Tolerance Of Elymus Sibiricus Under Water Deficit And Rewatering

Elymus sibiricus Linn.belongs to Elymus of Gramineae.This species is an important component of natural grassland plant community in the north of China,especially in the Qinghai-Tibet Plateau,and it is also an important parameter to judge the grazing quality of this kind of grassland.Most areas of the Qinghai Province is in semi-arid climate.Water deficit is an important environmental factor limiting forage production.Therefore,studying the drought adaptation mechanism of E.sibiricus and improving their water use efficiency has important theoretical research value and practical significance.In this paper,the germination and emergence,root cap physiology and biochemistry,root water absorption characteristics,root cap ultrastructure and water use of 15-195 E.sibiricus（wild species）and Qingmu No.1 E.sibiricus（cultivated species）were studied by using polymer penetrant PEG-6 000 and pot water control method to simulate the drought stress environment,It is expected to clarify the relationship between E.sibiricus and drought stress on the overall level,so as to provide theoretical basis and experimental data support for the breeding of new drought tolerance E.sibiricus varieties.The main results were as follows:（1）With the aggravation of water deficit,The bud,germination and seedling emergence percentage and bud,germination and emergence rate of E.sibiricus showed a downward trend.The starting time of bud,germination and seedling emergence and the high peak period of bud,germination and seedling emergence were delayed,and the high peak period of bud,germination and seedling emergence of E.sibiricus after rewatering still lagged.When water deficit occurred on the 3th,4th,6th days after rewatering and rewatering on the 3th,4th and 6th days,the 15-195bud,germination and seedling emergence high peak period under moderate and severe water deficit were the same,and the Qingmu 1 bud,germination and seedling emergence high peak period under each water deficit were the same.When water deficit occurred on the 6th days and on the second day of rewatering,the bud percentage,germination percentage and seedling emergence percentage of E.sibiricus under light water deficit were higher than those in the control group.Under different combinations of water conditions,with the aggravation of water deficit,the bud length of E.sibiricus decreased,and its root length,root-bud ratio and root number increased gradually;After rewatering,the root length,bud length and the ratio of root to bud were greatly improved,but the number of roots decreased gradually.Under water deficit and rewatering,the bud length of E.sibiricus under moderate and above water deficit was higher than that in the control group.When water deficit occurred on 4th,6th days and rewatering on the 3th,4th days,the bud length under each water deficit was higher than that in the control group.（2）With the increase of water deficit time,the production rate of O₂·^﹣,REC and MDA content in the root and crown of E.sibiricus increased,and decreased after rewatering.The SS content,Pro content,SOD activity,POD activity and CAT activity of 15-195 root and crowns increased,but decreased after rewatering.When water deficit was 24 hours,the SS content,Pro content,SOD activity,POD activity and CAT activity of Qingmu 1 reached the maximum.Under water deficit and rewatering,the SS content,Pro content,SOD activity,POD activity and CAT activity of roots of15-195 were higher than those of leaves,while Qingmu 1 was the opposite.According to the grey correlation analysis,the MDA content in roots and CAT activity in leaves of 15-195 have the greatest correlation with drought tolerance,while that the SS content in roots and O₂·^﹣in leaves of Qingmu No.1 have the greatest correlation with drought tolerance.（3）With the increase of water deficit time,the AQPs activity,hydraulic conductivity,total absorption area,active absorption area,specific surface area of seedling root system and the Pn,Gs,Tr and WUE of seedling leaves decreased,and gradually increased after rewatering.Under the treatment of mercuric chloride,the hydraulic conductivity of the root system of E.sibiricus under sufficient water supply was lower than that of the control group.Underβ-ME treatment,the hydraulic conductivity of the root system of E.sibiricus under sufficient water supply was higher than that of the control group.Under the condition of water deficit and rewatering,there was a linear positive correlation between root hydraulic conductivity and Pn,Gs and Tr,and a quadratic curve between WUE and root hydraulic conductivity.（4）Under water deficit and rewatering,the damage degree of chloroplast in root crown of E.sibiricus was greater than that of mitochondria.With the increase of water deficit time,chloroplasts,mitochondria and nuclear membrane of root crown of E.sibiricus showed different degrees of damage,but the number of mitochondria increased and the root cell wall partially thickened.Under water deficit,the damage degree of nuclear membrane and mitochondria of 15-195 root system was less than that of its leaves,while Qingmu 1 was the opposite.After rewatering,compared with leaf mitochondria,root system mitochondria of 15-195 recovered better,while that of Qingmu 1 was the opposite.Under water deficit and rewatering,Compared with Qingmu No.1,the damage and recovery degree of chloroplast,mitochondria and nuclear membrane of 15-195 root crown were better.（5）Under rewatering after light water deficit,the plant height,leaf area and hay yield of 15-195 were higher than those of the control group,and the plant height,leaf area and hay yield of Qingmu 1 were basically the same as those of the control group;under rewatering after moderate water deficit,the plant height,leaf area and hay yield of 15-195 were close to those of the control group,while the plant height,leaf area and hay yield of Qingmu 1 were lower than those of the control group;under rewatering after severe water deficit,the plant height,leaf area and hay yield of15-195 and Qingmu 1 were significantly lower than those of the control group.Under rewatering after drought,with the aggravation of water deficit,the root/total biomass,root/aboveground biomass and specific leaf weight of E.sibiricus showed an upward trend,while the stem/total biomass,leaf/total biomass and ear/total biomass showed a downward trend.Under rewatering after drought,According to the dynamic changes of hay yield,water consumption and water use efficiency at each development stage of E.sibiricus after drought rewatering,the water regulation and management of E.sibiricus can be divided into the following types:high yield and high water consumption type（sufficient water supply）,which is characterized by high hay yield and high water consumption;High yield and water-saving type（light water deficit）,which is characterized by high hay yield and high WUE,water consumption saves more water than the control group;Middle yield and high water saving type（moderate water deficit）,which is characterized by low hay yield,but can save a lot of water;Low yield and low water use efficiency type（severe water deficit）,which is characterized by low hay yield and significantly lower WUE than the control group.After rewatering,under light water deficit,the leaf water potential of E.sibiricus in each development stage approached the control group on the 10th day,its osmotic potential gradually recovered to the level of the control group after the 15th day,and the contents of Pro and SS were always higher than that of the control group.After rewatering at jointing stage,the increase of Pn rate of E.sibiricus was affected by stomatal limitation.The 5～15th days of rewatering at booting stage,the increase of15-195 Pn rate was affected by stomatal limitation;under the 15～22th days of rewatering,the decrease of Pn rate was affected by non-stomatal limitation;from the22th day of rewatering,the decrease of E.sibiricus Pn rate was affected by stomatal limitation.The 5～10th days of rewatering at heading stage,the increase of Pn rate of E.sibiricus was affected by stomatal limitation.under the 10～15th days of rewatering,the decrease of E.sibiricus Pn rate was affected by non-stomatal limitation;from the 15th day of rewatering,the decrease of E.sibiricus Pn rate was affected by stomatal limitation.The 5～10th days of rewatering at flowering stage,the decrease of E.sibiricus Pn rate was affected by non-stomatal limitation;from the15th day of rewatering,the decrease of E.sibiricus Pn rate was affected by stomatal limitation.