Ecological Adaptability Of Mono-/Mixed Cultured Medicago Sativa L. Under Drought Stress In Shanxi Mining Areas

Based on our preliminary studies on naturally colonized and planted community in Shanxi mining areas, three typical planted patterns of Medicago sativa L., including Mono-cultured Medicago sativa L. (M), mixed cultured Medicago sativa L.+Agropyron cristatum (M+A) and Medicago sativa L.+Poa annua L. (M+P), were taken as research targets owing to their strong drought tolerance, poor soil tolerance and strong ecological adaptability. These grasses were cultured in pot filling with raw mixed-loess and mellow soils collected from Shanxi coal mining areas in greenhouse for two years. And then a soil moisture gradient experiment of normal water (T1) (Control) with 75-80% of field capacity levels, medium drought (T2) with 55-60% of field capacity levels and severe drought (T3) with 35-40% of field capacity levels were conducted with three repetitions, and leaf water physiological index, antioxidant enzyme system, photosynthetic characteristics, soil enzyme activity of two-year mono-/mixed cultured Medicago sativa L. were measured under drought stress in the greenhouse by using biochemical techniques and photosynthesis system (Li-6400XT) to access the ecological adaptability of Medicago sativa L.. The main research contents and results were as follows:(1) Drought stress on water physiological characteristics of mono-/mixed cultured Medicago sativa L.Compared with T1 treatment, the relative water content (RWC) and chlorophyll content of mono-/mixed cultured Medicago sativa L. significantly decreased from 5.03% to 14.10%, and 15.33% to 25.09%, respectively under T2 and T3 treatments in raw mixed-loess and mellow soils, while their relative water deficit (RWD) of leaves significantly increased from 20.75% to 100.28% under T2 and T3 treatments (p<0.05).(2) Effects of drought stress on antioxidant system of mono-/mixed cultured Medicago sativa L.Compared with T1 treatment, the superoxide dismutase (SOD) activity, peroxidase (POD) activity and malondialdehyde (MDA) content of Medicago sativa L. (Mono-/Mixed Cultured) increased significantly (p<0.05) under T2 and T3 treatments in raw mixed-loess and mellow soils. Under T3 treatment, the SOD and POD activity of Medicago sativa L. (M) increased larger than that of mixed cultured Medicago sativa L. in raw mixed-loess soil matrix with the value of 39.22% and 105.88%, respectively; the SOD and POD activity of Medicago sativa L. (M+P) increased largestly among three planted patterns of Medicago sativa L. with the value of 45.97%å'Œ119.80%, respectively. The MDA content of Medicago sativa L. (M) was higher than that of mixed cultured Medicago sativa L., and its ascending range and membrane lipid peroxidation were higher than that of mixed cultured Medicago sativa L. in the two soil matrixes.(3) Effects of drought stress on photosynthetic characteristics of mono-/mixed cultured Medicago sativa L.Compared with T1 treatment, the net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE) and stomatal conductance (Gs) of mono-/mixed cultured Medicago sativa L. decreased significantly (p<0.05) under T2 and T3 treatments in raw mixed-loess and mellow soils, respectively. The decreasing amplitudes of Pn, Tr, Gs in Medicago sativa L. (M) were less than that of mixed cultured Medicago sativa L., the WUE of Medicago sativ L. (M) decreased slightly larger than that of mixed cultured Medicago sativa L. under T3 treatment in raw mixed-loess soil. While the decreasing amplitudes of Pn, WUE and Gs of Medicago sativa L. (M+P) were the smallest among the three planted patterns of Medicago sativa L. under T3 treatment in mellow soil.(4) Effects of drought stress on soil enzymes activities in the rhizosphere of mono-/mixed cultured Medicago sativa L.Compared with T1 treatment, the activities of soil urease enzymes and sucrose enzymes in the rhizosphere of mono-/mixed cultured Medicago sativa L. decreased significantly under T2 and T3 treatments in raw mixed-loess soil and mellow soil (p<0.05). In addition, the activities of soil enzymes including soil urease enzymes, sucrose enzymes and alkaline phosphatase enzymes in raw mixed-loess soil were lower than that of in mellow soil for mono-/mixed cultured Medicago sativa L(5) Evaluation of ecological adaptability of mono-/mixed cultured Medicago sativa L. under drought stressThe drought resistance of mono-/mixed cultured Medicago sativa L under drought stress was evaluated by the method of subordinate function and their rank order from high to low in raw mixed-loess soil were: Medicago sativa L. (M)> Medicago sativa L. (M+A)> Medicago sativa L. (M+P) under T2 treatment and Medicago sativa L. (M)> Medicago sativa L. (M+P)> Medicago sativa L. (M+A) under T3 treatment, respectively. While their rank order from high to low in mellow mixed-loess soil were:Medicago sativa L. (M+P)> Medicago sativa L. (M)> Medicago sativa L. (M+A) under T2 and T3 treatments. Thus it could be concluded that drought resistance of Medicago sativa L. (M) was higher than that of mixed cultured Medicago sativa L. in raw mixed-loess soil, but the drought resistance of Medicago sativa L. (M+P) was higher than that of Medicago sativa L. (M) in mellow mixed-loess soil. And the drought resistance of mono-/mixed cultured Medicago sativa L. in raw mixed-loess soil was lower than that of cultured Medicago sativa L. in mellow mixed-loess soil. The evaluation results were same by analyzed the methords of system clustering analysis and subordinate function.Above all, from the point of view of plant physiology and ecology, it is suggested that the pattern of mono-cultured Medicago sativa L. is better for revegetation in raw mixed-loess soil and the pattern of mixed cultured of Medicago sativa L. (M+P) is better for revegetation in mellow soil (ie. topsoil covering) at the practice of mineland revegetation in Shanxi mining areas with drought and poor soil conditions.