Ecological Adaptability Of Four Herbaceous Plants Under Drought Stress In Mining Regions Of The Plateau Loess

Based on the field vegetation survey of natural coloning and planted communites and pilot study on mining regions of the Loess Plateau, the four typical herbaceous plant species of Medicago sativa, Poa annua, Agropyron cristatum and Lolium perenne with strong drought tolerance, poor soil tolerance and extensive ecological adaptability were screened and used as the plant materials in the greenhouse planting experiment for water control, and the coal gangue covering raw mixed-loess soils used as the soil matrix. Three different soil moisture gradients of water control (normal water with 75-80% of field capacity levels, medium drought with 55-60% of field capacity levels and severe drought with 35-40% of field capacity levels) were set and each of the gradients repeated three times. By using the photosynthesis system (LI6400XT) and denaturing gradient gel electrophoresis (PCR-DGGE), the effects of the four herbaceous plants in mono- and mixed- culture under drought stress were studied, including the four kinds of herbaceous plants growth condition and water physiological indicator under the three soil moisture gradients of drought stress, plant tissue antioxidant enzyme system, soil microbial community diversity and the plant photosynthetic physiological characteristics, etc. The main results were as follows:(1) In severe drought stress, the overground biomasses and heights of four herbaceous plants were significantly lower than that of the normal water condition and medium drought stresses (p<0.05), which indicated that a severe shortage of water in soil hindered the growth of plants. The height and overground biomass of Lolium perenne under slight drought stress and severe drought stress were significantly lower, part of the plant were wilting and death. Plant height and aboveground biomass of Agropyron cristatum under medium drought stress slightly changed, Medicago sativa and Poa annua took second ranks. It showed that Agropyron cristatum drought resistance was the strongest, followed by Poa annua and Medicago sativa, the most weak drought resistance was Lolium perenne.(2) With the increase of drought stress, the malondialdehyde (MDA) content of the four kinds of herbs were increased, the MDA content of Agropyron cristatum in medium and severe drought stress was the smallest, the MDA content of Lolium perenne increased greatly, it showed that the Lolium perenne oxidative stress damage is the most serious. In medium and severe drought stress, the glutathione peroxidase (GPX) activity of four herbs increased gradually. With the increasing of drought stress, the superoxide sismutase (SOD) activity of Medicago sativa, Poa annua and Lolium perenne increased significantly, while the Agropyron cristatum had no significant change. Under the medium and severe drought stress, Agropyron cristatum peroxidase (POD) decreased, while the POD activities of Medicago sativa, Poa annua and Lolium perenne increased since the drought stress. Study on antioxidase enzyme systems of herbaceous plants showed that:four kinds of herbaceous plants could regulate the activity of antioxidant enzymes to resist drought stress, and Agropyron cristatum has the strongest the antioxidant capacity.(3) Under the drought stress, the maximum net photosynthetic rate for four typical herbaceous plants had the following order:Agropyron cristatum> Medicago sativa> Lolium perenne> Poa annua. Agropyron cristatum had stronger adaptive ability to drought stress. With the increase of drought stress, the light saturation point for four herbaceous plants decreased, while the light compensation point gradually increased. It indicated that the light use capabilities of the four herbaceous plants were weakened for high or low light intensity, and the the available energy range were also reduced. Water use efficiency of Poa annua, Agropyron cristatum and Lolium perenne could be improved under drought stress, while water use efficiency of Medicago sativa was low due to the high transpiration under severe stress. Fall in stomatal conductance, intercellular CO2 concentration decreased at the same time, the stomatal conductance of Lolium perenne and Agropyron cristatum presented first reduced trend then increased trend, it suggestted that these two plants stomatal conductances decreased at the same time, the stomatal limitation and the stomatal limitation factors, and Medicago sativa and Poaannua showed a trend of falling, this was an adaptation of drought of Agropyron cristatum and Medicago sativa on the water condition.(4) Gene band of rhizosphere microorganisms at each of the four herbaceous plants (Medicago sativa, Poa annua, Agropyron cristatum and Lolium perenne) were significantly different under different drought stress, which performanced as:normal water condition> medium drought stress> severe drought stress. Under severe drought stress, the rhizosphere microbial genes of Poa annua were significantly less than that of the normal water condition. Under medium drought stress and severe drought stress, the band of soil microbial of Medicago sativa was less than that of normal water condition. Soil microbial diversity of Medicago sativa and Poa annua was as follows:Medicago sativa> Poa annua. Agropyron cristatum has more abundant soil microbial species in the medium and severe drought soil environment. Lolium perenne has 3 joint gene bands in medium and severe stress, these kinds of microbial soil moisture insensitive to changing conditions.Overall, Agropyron cristatum and Medicago sativa have the strong drought tolerance ablilties, which are the best herbaceous plant species for ecological restoration of mining area on the Loess Plateau materials.