Abstract: Background, aim, and scope Some of large coal enterprises in Inner Mongolia have been striving to develop coal-fired power plants and promoting the integration of coal and electricity, which leads to the rapid increase of coal consumption in Inner Mongolia. During the coal combustion, the phenomenon of mercury emissions into the atmosphere appears, which results in a serious of impacts on environmental pollution. Therefore, this paper studied the mercury enrichment capacity of various pasture and their tolerance to mercury through the experiment of mercury stress in pasture in Inner Mongolia. Materials and methods The experimental materials included Leymus chinensis, Medicago sativa, Elymus dahuricus, Festuca elata,[lyj1] the pasture and seeds were provided by the grassland station of the Chinese Academy of Sciences in Dongwuzhu, Inner Mongolia, the experimental soil was collected from grassland of Chinese Academy of Sciences in Dongwuzhu, Inner Mongolia. The method of microwave digestion was used to determine mercury content of plant and soil, malondialdehyde (MDA) was determined by colorimetric method, the soluble protein was determined by coomassie brilliant blue staining, the soluble sugar content was determined by anthrone method. Results In the case of low concentration of mercury, all the four kinds of pasture had certain adsorption capacity on mercury, but when the concentration of mercury in the soil continued to increase, four kinds of pasture mercury enrichment effect was not as expected, not like enrichment plant. When the mercury concentration in soil was not higher than that of the soil quality standard, the enrichment coefficient of the four pastures were all greater than 1, which had the better ability to accumulate mercury. Average mercury adsorption efficiency of Leymus chinensis was 26.22%, followed by Elymus dahuricus, the adsorption efficiency was 24.61%, again is Festuca elata, the adsorption efficiency was 22.69%, the lowest was Medicago sativa, the adsorption efficiency was 15.57%. It can be used to extract mercury contaminated soil.The correlation between heavy metals in plant and soil is related to the physiological characteristics of plant, indicating that the mercury content in herbage is related to the mercury content in soil. With the increase of mercury stress concentration, the content of malondialdehyde (MDA) in the four kinds of pasture showed the trend of the first decrease and then rise. After reaching the lowest value, the MDA content of the four pastures increased with the increase of mercury stress concentration. Among them, Medicago sativa had the greatest change in MDA content under mercury stress, so it was the most affected. When the mercury stress concentration was 64.0 mg·kg-1, the content of the four kinds of pasture was the highest, 7.48 times, 5.63 times, 3.42 times and 4.02 times of the control group. Among the four kinds of pasture, Leymus chinensis was the most powerful for the stress resistance of mercury. Discussion Refers to some kind of heavy metal content in plant enrichment coefficient and the ratio of this kind of heavy metals in soil original content, can reflect the enrichment ability of plants to heavy metals, the greater the enrichment coefficient, said its accumulation ability is strong. Four kinds of pasture have adsorption effect on mercury in soil at various levels of mercury stress. The mercury content in pasture was correlated with mercury content in soil. Malondialdehyde and proline can reflect mercury's physiological toxicity to plants. ConclusionsThe mercury accumulation in plants was significantly affected by different concentrations of mercury stress. Four kinds of pasture have certain adsorption and transfer ability to mercury in soil. When the mercury stress concentration was low (<16.0 mg·kg-1), Medicago sativa had the strongest adsorption capacity. After the increase of mercury stress concentration (>16.0 mg·kg-1), Elymus dahuricus had the strongest adsorption capacity.The mercury enrichment coefficient was decreased with the increase of mercury stress concentration, among which the maximum enrichment coefficient was the highest. Mercury stress has a significant effect on the physiology of different pasture. When the mercury content in soil is too high, it can have a toxic effect on the growth of four kinds of pasture. Under the effect of a certain concentration of mercury stress, the pasture by raising the proline content, promote the antioxidant enzymes enzyme activity, reduce the stress caused by mercury higher reactive oxygen species, as well as the level of membrane lipid peroxidation, equilibrium cell osmotic pressure and environment necessary to sustain the plant normal growth. Recommendations and perspectivesInner Mongolia is a coal producing province, and the economic development model of coal-power integration should be promoted in the long-term planning and protection of grassland ecology. As a result, the amount of coal will be released as well as the increase of coal-fired power generation. Proper measures should be taken to control the mercury content in flue gas of coal-fired power plants and to prevent the emission of long-term and low concentration mercury from coal-fired power plants in grassland vegetation.
Keywords: pasture; mercury; accumulation characteristics; physiological response