| Carex breviculmis is one of the ideal herbaceous plants for turfgrass.It has good drought tolerance and has good application in landscaping in northern China.Melatonin is a hormone that exists widely in nature.It has a certain promotion effect on plant growth and resistance.Exploring the mechanism of exogenous melatonin on plant stress resistance can effectively evaluate the application value of melatonin in landscaping.In this study,Carex breviculmis seedlings were used as experimental materials,different concentrations of exogenous melatonin were applied,and the natural water control method was adopted to simulate drought treatment.The root architecture index,root physiological index and anatomical structure were measured to explore the exogenous source.The change characteristics of melatonin on the physiological and morphological indexes of the root system in response to drought stress on Carex breviculmis.The optimal concentration of exogenous melatonin on the root morphology to adapt to drought stress stress changes is summarized,which provides for its rational use in landscaping Certain scientific basis.(1)With the extension of the drought stress time,the total root length,root surface area,total root volume,root dry weight,and average root diameter of Carex breviculmis at each concentration showed a trend of increasing first and then decreasing.The number of root bifurcations showed a continuous upward trend.The root-shoot ratio and root weight density showed a trend of increasing first and then decreasing,while the specific root length showed a trend of decreasing first and then gradually stable.Under the condition of 100 μmol/L exogenous melatonin applied to the roots,most of the above indicators were the best on the 20th day,and the effect was the most obvious,which significantly alleviated the influence of drought stress on the root architecture of Carex breviculmis.(2)With the early stage of drought stress,the growth rate of the above-ground part is faster than that of the underground part.From 10 to 20 days,the growth rate of the underground part accelerated.Although the root system gradually sprouted new lateral roots and fibrous roots,and the underground part of the main root is thicker,but at the same time,the fragile and dry fibrous roots are detached.It shows that the response of the underground part to drought stress is later than that of the above-ground part.With the early stage of drought stress,the growth rate of the above-ground part is faster than that of the underground part.From 10 to 20 days,the growth rate of the underground part accelerated.Although the root system gradually sprouted new lateral roots and fibrous roots,and the underground part of the main root is thicker,but at the same time,the fragile and dry fibrous roots are detached.It shows that the response of the underground part to drought stress is later than that of the above-ground part.(3)With the prolongation of drought stress,the root diameter,vessel diameter,vascular bundle diameter,cortex thickness,and the ratio of cortex thickness to root diameter in each group showed a trend of first increasing and then decreasing,and the number of vessels showed a trend of increasing first and then gradually stabilizing.Under the influence of drought stress,the changes in root anatomical structure improve the ability of water absorption and drainage.Thickening of the cortex increases the amount of water stored in the root cortex cells,ensuring the supply of water during root growth and metabolism.On the 20th day,all the indexes of the 100 μmol/L experimental group were the highest,indicating that the root anatomical structure has a stronger ability to adjust itself to drought stress,and the drought resistance is stronger than that of the other three groups.(4)In the early stage of drought,the anatomical structure of the root system in each group was clear and complete,the Kjeldahl band structure was obvious,the xylem duct space was full,and the cell arrangement was different and tight.The shape is fairly complete,the area of the center column has been improved,and the structure is relatively complete.The parenchyma cells inside the center column begin to deform and gaps appear.The root cortex gradually shrinks and becomes thinner due to the dense and compact structure,which is caused by certain damage to Kjeldahl.In the subsequent stages,the central pillars of each group showed varying degrees of damage and shrinkage.The order of the central pillars was also broken,and there were stratified necrotic spots.The xylem ducts continued to become thinner and more and more countermeasures were taken to overcome them.,On the 20th day,the root anatomical indexes of the 100 μmol/L group were the best and the root anatomical structure was reduced intact,and the staining was clearer.(5)With the prolongation of drought stress,the damage of cell membrane was serious,and the content of MDA,the product of membrane lipid peroxidation in each group,showed a rising trend.Among the osmotic adjustment substances,the content of Pro and the content of soluble sugar show a rising trend with the extension of the drought time.The content of soluble protein in each group showed a trend of increasing first and then decreasing.The SOD activity and POD activity of antioxidant enzymes showed a trend of first increasing and then decreasing with the extension of drought time.The latter was greatly affected by drought,which affected the synthesis of osmotic adjustment substances and antioxidant enzymes.Among them,the 100 μmol/L experimental group had the lowest MDA content on the 20th day,the cell membrane was less damaged,and the drought stress had little effect on it,the osmotic regulators and antioxidant enzymes had the highest activity,and the ability to resist drought was the most stronger.In summary,combined with the analysis of multiple experimental indicators,the exogenous melatonin solution at a concentration of 100 μmol/L can significantly improve the root structure parameters,physiological indicators,anatomical structure and drought resistance of Carex breviculmis. |
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