| In the double pressure of world energy crisis and the increasing depletion of arable land resources, developing a number of high economic value of energy plant on the heavy metal contaminated soils or mine tailings becomes an efficient and important way to restore contaminated soils and relieve the energy crisis. Pasture plants have great potential of using as energy plants with its characteristics of low-cost, easy management, well ecological adaptability, high-yielding, and short production cycle, but its resistance to heavy metals remains to be further explored. In this study, two different varieties of guinea grass Panicum maximum var. Natsukomaki and Panicum maximum var. Natsukaze were used to study the effects of different concentrations of copper in guinea grass seedlings, and the protect role of paclobutrazol pretreatment on the copper toxicity to guinea grass. The main results are as follows:1. Hydroponic experiments were used to study the effect of different copper concentration on guinea grass seedlings, results showed that:with increasing concentration of copper treatment, the seedlings accumulation of copper content gradually increased, and mainly accumulated in the roots of plants. Copper stress inhibited the growth of grass seedlings, reduced plant height, root length, fresh and dry weight of shoots and roots, as well as injuryed the roots, so that reduced root activity. Copper stress can lead to the degradation of chlorophyll or hindering its synthesis, so the chlorophyll in guinea grass leaves reduced gradually with increasing copper concentration, but different leaves responsed differently to excessive copper. Copper caused the greatest impact in the first leaves (top down), next the second leaves, and the chlorophyll content of the third leaves were relatively stable. The parameters of Natsukomaki and Natsukaze had the similar trend under copper stress, but their sensitivity was ssslightly different, we got the semi-lethal concentration of copper for the two guinea grass from the fitting curves of their fresh weight variation, and the EC50 for Natsukomaki and Natsukaze were 245.89μmol/L and 308.59μmol/L respectively. Integrating with all indicators, Natsukaze had better copper tolerance than Natsukomaki.2. In field experiments, to the control soil in Dou village, soil in Tangshan funiu village was polluted by copper mine tailings. Comparing the growth condition of two varieties of guinea grass in both places, we found that the surface layer soil (0-20cm) in funiu village with copper content of 869.2mg/kg, which beyond the third class of the national stanhard of soil environmental quality (<400mg/kg), can cause toxicity to some copper-sensitive plants. There is a comfort that the guinea grass growed in funiu village did not show obvious injured symptoms when exposured to copper stress, and there were no significant differences of plant biomass and unit values between two varieties of guinea grass growing in different test fields, but the biomass and values of per plant for Natsukaze were higher than Natsukomaki, indicating that both guinea grass have well resistance to copper stress, moreover Natsukaze has more advantage than Natsukomaki.3. In hydroponic cultures, the guinea drass leaves spraying with different concentrations of paclobutrazol (200,400,600 mg/L), which alleviated the copper stess to plant seedlings. We found that the plant pretreated with paclobutrazol only had developed root system, increased number of branches, as well as higher fresh and dry weight than control seedlings, indicating paclobutrazol can significantly promote the growth of guinea grass. The same time, under 300μM copper stress, paclobutrazol can reduce the adsorption of copper in plants, mitigated the reduction of plant height, fresh and dry wejght, total chlorophyll content in leaves of seedlings, increase TTC deoxidization activity of roots, also can inhibit the free proline and soluble sugar accumulation, thereby increasing the resistance of guinea grass to copper stress, while the 400 mg/L paclobutrazol concentration for pretreatment acted as the best. |
