Effects Of Water Stress On The Growth And Physiological Characteristics Of Seedlings Of Achnatherum Inebrians

Water deficit affects the growth,development,and physiological function of plants.The adaptability of plants to water stress determines their distribution in the ecosystem,which is an objective expression of adapting to the external environment.Achnatherum inebrians（drunken horse grass）is a poisonous grassland grass in arid and semi-arid areas of Northwest China.It has the characteristics of strong stress resistance and nonfeeding of livestock.It shows a trend of expansion and spread.It is distributed in desert grassland,grassland and meadow grassland,and has strong water adaptability.In this study,the growth characteristics,leaf structural anatomy,physiological response,and adaptability to water stress of drunken horse grass seedlings during normal watering and continuous water stress were studied through a greenhouse pot experiment,so as to provide theoretical reference for revealing the drought resistance mechanism of drunken horse grass and formulating scientific prevention and control measures.The main results are as follows:（1）In terms of growth characteristics,with the extension of continuous water stress,the number of leaves and effective leaves decreased（P<0.05）,while the number of dead leaves increased（P<0.05）.Early water stress increased the growth of leaf length,leaf width,and leaf area,but decreased after water stress（P<0.05）.Water stress promoted the growth of plant height and aboveground,underground,and plant biomass,but decreased with the extension of water stress to 21 days（P<0.05）,while the distribution of underground biomass increased（P<0.05）.After rewatering for 7 days,there was no significant difference between the indexes and the control（P>0.05）,and the growth of drunken horse grass recovered.It can be seen that the growth of drunken horse grass seedlings is hindered under water stress,but they improved water use by reducing leaf area to reduce water transpiration area and increasing belowground biomass allocation,and were able to resume normal growth quickly after water stress was removed.（2）In the aspect of leaf structural anatomy,water stress increased the vascular tissue diameter,vascular bundle diameter,vascular tissue area,vascular bundle area,and vascular bundle sheath area of drunken horse grass（P<0.05）.The thickness growth of leaf lower epidermis was first inhibited and then promoted,increasing from93.75μm to 117.02μm（P<0.05）;There was no significant difference in leaf thickness,leaf upper epidermis thickness,mesophyll tissue thickness,vascular bundle sheath thickness,and xylem area among treatments（P>0.05）.After rewatering,except for the thickness of the leaf lower epidermis,other indexes of leaf structure resumed growth.It can be seen that the growth of drunken horse grass leaves was hindered under water stress,and resistance to water stress was achieved by increasing the area of the vascular tissue of the leaf veins.After water recovery,the leaf vein vascular tissue increases the water conveyance function,preferentially transports underground water to the leaves,and the leaves can grow normally.（3）In physiology,water stress reduced stomatal conductance,transpiration rate,water use efficiency,intercellular CO₂ concentration,and net photosynthetic rate（P<0.05）,and water use efficiency reached the maximum at 21 days of water stress（P<0.05）;After rewatering,except for intercellular CO₂ concentration and net photosynthetic rate,there were significant differences in stomatal conductance,transpiration rate and water use efficiency between drunken horse grass and the control（P<0.05）.It can be seen that under water stress,the gas exchange is blocked,the stomatal opening is reduced,the water transpiration rate is reduced,the water use efficiency is increased,the intercellular CO₂ concentration is reduced,and then the net photosynthetic rate is reduced;After rewatering,the respiration of drunken horse grass increased and the photosynthetic function recovered.At the beginning of water stress,chlorophyll content and peroxidase activity increased（P<0.05）.After rewatering for 7 days,the soluble sugar content,superoxide dismutase,peroxidase,and catalase activities were significantly different from CK（P<0.05）,while the contents of chlorophyll,malondialdehyde,proline,and soluble protein were not significantly different from CK（P>0.05）;It can be seen that drunken horse grass can prevent the membrane lipid peroxidation caused by malondialdehyde by increasing the activities of chlorophyll,osmotic regulators and antioxidant enzymes,increase superoxide dismutase and catalase,reduce the enzyme activity of peroxidase,remove reactive oxygen species in cells,maintain the metabolic homeostasis in cells,to increase the abscission of dead leaves and promote the growth of new leaves;After water recovery,the growth of drunken horse grass was restored by increasing the activity of antioxidant enzymes to remove reactive oxygen species in cells.In conclusion,drunken horse grass seedlings adapted to water stress by reducing plant height and leaf area,increasing root-shoot ratio and leaf vein lignification,decreasing photosynthesis and improving water use efficiency;increasing chlorophyll,proline,soluble sugar,soluble protein content and superoxide dismutase and catalase enzyme activities,and decreasing peroxidase enzyme activity.