Study On Rapid Cultivation Of Moss-dominated Crusts On Loess Plateau And Their Physiological Response To Stress

Biological soil crusts is a common bioactive ground coverage in arid and semi-arid regions and has very important ecological functions in ecosystem in these regions. Moss-dominated crusts is the advanced stage of development and succession of biological soil crusts on Loess Plateau, China, and they plays an important role in accelerating the formation of soil, improving soil physical and chemical properties, increasing the anti-erosion ability of soil and reducing the loss of soil and water. The studies on rapid cultivation of moss-dominated crusts on Loess Plateau and physiological response of their dominated species to drought and rewatering and high temperature stress, which can provide experimental basis and theoretical guidance to rapid restoration and scientific cultivation of moss-dominated crusts on Loess Plateau. Naturally development moss-dominated crust, which dominant specie is Didymodon vinealis(Brid.) Zand., on Loess Plateau was chose as seed in this research, and studying the effects of different light intensity, soil moisture in top layer, nutrient solution, sugar and plant growth regulator factors on the grow and development of moss-dominated crusts in phytotron by using single-factor and orthogonal design. Meanwhile, artificial bryophytes, which is dominated by Didymodon vinealis(Brid.) Zand., is taken as the study object, their physiological response to drought and rewatering and high temperature stress was also studied in this research. The main research results as follows:(1) Soil moisture content in top layer(1%-30%), light intensity(1000-23500 lx) and inoculation amount(250-700 g/m2) had extremely significant effect on the coverage, plant density and biomass of moss-dominated crusts. The the coverage, plant density and biomass of moss-dominated crusts increased with the increase of soil moisture content in top layer and inoculation amount. The development rate of moss-dominated crusts increased with the decrease of light intensity. The effects order of the three factors to the coverage and plant density of moss-dominated crusts was: top soil moisture > light intensity > inoculation amount; as for biomass, the effects order of the three factors was: top soil moisture > inoculation amount > light intensity. Soil moisture in top layer was the most important factor for affect the rapidly cultivation of moss-dominated crusts on Loess Plateau among three factors in this researches.(2) All of Hoagland, modified Knop, Part, Beneck and MS solution could increase the coverage, plant density and biomass of moss-dominated crusts, the increased degree of these solutions was varies by the kind of solution. At the end of cultivation period(on 65 th day), the coverage, plant density and biomass of moss-dominated crusts of Hoagland treatment was the greatest among six treatments, and increased by 35.23%, 124.60%, 56.48%, compared with those of distilled water treatment(CK), respectively. During the whole process of cultivation experiment, compared with distilled water treatment(CK),Hoagland, modified Knop, Part and Beneck solution increased the height of plant in different degrees, and MS solution treatment reduced the height of plant.(3) Sucrose, glucose and mannitol can promote the development of moss-dominated crusts at different degrees, and sugar could inhibited the development of moss-dominated crusts when its concentrations greater than 10 g/L. During the initial stage of the cultivation experiment(on 25 th day), compared with distilled water treatment, different concentration sugar solution decreased the coverage, plant density and plant height of moss-dominated crusts, and decreased degree was positively related with sugar concentrations. With the decreasing of sugar concentrations in soil, the increasing rate of coverage, plant density and plant height of moss-dominated crusts of different concentration sugar solution was greater than those of distilled water treatment. At the end of the cultivation experiment(on 65 th day), the coverage, plant density and plant height of moss-dominated crusts of different concentration sugar solution was greater than those of distilled water treatment. The coverage and plant density of moss-dominated crusts of 30 g/L glucose treatment was the greatest among all treatments, which were reached 80.96 % and 68.04 plant/cm2, respectively. The plant height of moss-dominated crusts of 30 g/L sucrose treatment, which was reached 1.16 mm, was the highest among all treatments. The biomass of different concentration sugar solution treatment were lower than that of distilled water treatment, the biomass of 30 g/L sucrose treatment(0.64 μg/cm2) was the lowest among all treatments, which was decreased by 29.37% compare with that of distilled water treatment(CK).(4) The effects of plant growth regulators on the development of moss-dominated crusts was different with their kind and concentration. With the increase of concentration, butyl, kinetin, indole butyric acid and thidiazuron, 4 kinds of plant growth regulators displayed a tendency of inhibit to the development of moss-dominated crusts. Cytokinins had no significant influence on the coverage, plant density and height of moss-dominated crusts no matter its concentration was high or low. The effects of one kind of plant growth regulators on different index was also different. Compared with the distilled water treatment(CK), 10 mg/L butyl treatment decreased the coverage and plant density of moss-dominated crusts, and increased the plant height of moss-dominated crusts. During the whole cultivation experiment, the coverage and plant density of moss-dominated crusts of 3 concentrations of naphthalin acetic acid treatment were lower than that of distilled water treatment, and plant height of moss-dominated crusts of 2 mg/L naphthalin acetic acid treatment was always greater than that of distilled water treatment. The promotion effect of 1 mg/L thidiazuron on the development of moss-dominated crusts was the most obvious one among 6 kinds of plant growth regulators, at the end of the cultivation experiment, the coverage, plant density, plant height and biomass of moss-dominated crusts of 1 mg/ L thidiazuron was increased by 25.88%, 58.39%, 13.40%, 45.83%, compared with those of distilled water treatment, respectively, and all the difference reached significant level(p<0.05).(5) The best culturing conditions of rapid cultivate moss-dominated crusts on Loess Plateau was: top soil moisture is 25-30% + light intensity is 1000 lx + inoculation amount is 700 g/m2 + Hoagland solution. The coverage, plant density and height of moss-dominated crusts could reached 83.38%、122 plant/cm2、1.15 mm in 65 days, respectively.(6) During the process of drought and rewatering, activities of protective enzymes(superoxide dismutase, peoxidase and catalase), malondialdehyde content and osmoregulation substance(soluble sugar, soluble protein) of artificial bryophyte, which was dominated by Didymodon vinealis(Brid.) Zand., were increased at first and then decreased, while soil moisture content in top layer presented the opposite trend. With the extension of drought stress time, activities of protective enzymes, malondialdehyde content and osmoregulation substance content of bryophyte were continuously increased. At the end of drought stress period, compared with constant watering treatment(CK), the activities of peoxidase, superoxide dismutase, catalase, malondialdehyde content, soluble sugar content and soluble protein content increased by 51.63%, 273.52%, 599.24%, 340.78%, 107.24%, 65.59%, respectively. After the first day of rewatering, all of these indexes rapidly declined. With the increase of rewatering days, all of these indexes declined gradually and close to those of constant watering treatment(CK). These indicated that artificial bryophyte had strong resistance to drying wetting cycle environment.(7) With the increase of temperature, activities of protective enzymes, osmoregulation substance content and malondialdehyde content of artificial bryophyte increased by different extent. Take the first hour of high temperature stress as an example, compared with 20℃ treatment(CK), the activities of superoxide dismutase, peoxidase, catalase, soluble protein content, soluble sugar content and malondialdehyde content of artificial bryophyte of 45℃ treatment increased by 22.71%, 17.52%, 19.38%, 29.79%, 15.11%, 12.83%, respectively, except the soluble sugar content, the difference of other indexes were reached significant level(p<0.05). With the prolong of high temperature stress time, different index showed different trends of variation. With the increase of high temperature stress time, the activities of superoxide dismutase, peoxidase, catalase and soluble protein content of artificial bryophyte were increased at first and then decreased, and the content of soluble sugar and malondialdehyde increased slowly. These results indicated that bryophytes which were cultivated in artificial environment had a certain heat tolerance to short time high temperature stress, however, they could not resist the long time high temperature stress. Therefore, before move artificial moss-dominated crusts from artificial environment to nature environment, it is necessary to take some heat acclimation to artificial moss-dominated crusts.