| This experiment researches three kinds of preponderant seeds that distribute widely in drid and semiarid area of loess plateau. The seeds are Melilotus alba, Salix psammophila and Hedysarum scoparium. The researcher does pot experiment and Artificially controlling water in three different water conditions.:the suitable water treatment that have 70%~75% water of maximum moisture capacity (ck); the stress treatment of medium drought that have 50%～55% water of maximum moisture capacity(MD); the stress treatment of serious drought that have 35%~40% water of maximum moisture capacity (SD), in order to research the water consumption laws and property in drought resistance of these three plants. Besides, the researcher tries to give the plants'comprehensive evaluations of drought resistances for the purpose of supplying theoretical foundation of choosing suitable plant for forestation and restoration in loess plateau.Firstly,manifestation of three subjects investigated in different water conditions is that the relative water content in condign water is the largest, then the relative water content in stress treatment of medium drought, the smallest quatity is that in the stress treatment of serious drought. In different stress treatments, the daily water consumptions are different clearly. The peak value of daily consumptive uses of water appears form the mid-june until August,then tends towards stability and water consumptions tapers.Besides, the paek value of water consumptions in every ten days and monthly also appears from the mid-june until August that same as daily water consumption. To campare water consumptions of the three subjects investigated, the descending order is Melilotus alba,Salix psammophila and Hedysarum scoparium in conditions of condign water and stress treatment of medium drought,but in the stress treatment of serious drought, the descending order is Melilotus alba, Hedysarum scoparium and Salix psammophila.The reasercher finds that the daily water consumptions processes of the three preponderant seeds are different.Water consumptions of Melilotus alba and Salix psammophila reach peak from midday to 2pm,and from 2pm to 4pm,water consumptions declines,in other words,the changes of water consumptions are unimodal curves;the change of Hedysarum scoparium's water consumption process is bimodal curve as it has two peak value 10am and 2pm but declines at midday. In short,the three subjects investigated in their whole growing seasons have clear different water consumptions in different solid water conditions.Secondly, the stress treatments of drought exert remendous influences on physical signs of the three subjects investigated. Water consumptions of three plants in different water consitions are like that relative water content in condign water is larger than that in stress treatment of medium drought,and that in tress treatment of serious drought is fewer. Each plant in the same growing season also has clear difference between another one. Numerically,Melilotus alba and Salix psammophila in the stress treatment of medium drought and seriouse drought have less water consumption than Hedysarum scoparium. Test of water conservation capacity of leaf shows that water loss of Salix psammophila leaf is less than the others.The MDA contents and O2- content of three dominant species under different water treatment have clear difference between each other. But in numerical, the MDA content of Hedysarum scoparium under drought stress is slightly less than the index of other two spiecies ;The O2- content extremely significant difference in numerical: Melilotus alba>Salix psammophila>Hedysarum scoparium. The trends of antioxidant enzyme activities in three species were similar,which increased with the stress time and the antioxidant enzyme activities under water stress were higher than the control. Comparisons between various materials, the change of SOD contents under different water treatments is : Salix psammophila>Melilotus alba>Hedysarum scoparium ;the changes of CAT contents under different water treatments is : Hedysarum scoparium>Salix psammophila>Melilotus alba; the changes of POD contents under different water treatments is : Melilotus alba>Salix psammophila>Hedysarum scoparium.Lastly, to adapt drought stress the three species have their own characteristics. It is not comprehensive to evaluate the drought-resistant characteristics of subjects investigated on the basis of single indicator. In the end, by subordinate function analysis, the capacity of drought resistance of three pastures decrease in order of Hedysarum scoparium> Salix psammophila> Melilotus alba. |
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