| Cadmium (Cd) was one of the main heavy metal pollutants in the soil now, when it get to a certain concentration in plants, it would hinder the normal accumulation of material and energy metabolism of plants which affected plant growth. Pennisetum was annual or perennial forage grass, suitable for cultivation in South China, which was tall, stem and leaf were luxuriant and the root was developed, with large biomass, strong tolerance and the high content of crude protein and other excellent characteristics, which was as well as the energy grass and ornamental grass. Test was to study the cadmium stress about Pearl millet(Pennisetum americanum), Hybrid Pennisetum(P.americanum ×Rpurpureum) growth performance, physiological characteristics, photosynthetic characteristic, heavy metal accumulation characteristic and nutrition characteristic at three growth stages (seedling stage, tillering stage and heading stage), to explore the effect on pennisetum resist cadmium and cadmium enrichment in soil, and then to provide a theoretical reference on remediation of cadmium contaminated soil by pennisetum and screened better plants resistant to cadmium. The results were as follows:(1) At the same growth period, with the increase of Cd2+ concentration, firstly two Pennisetum plant height increased and then decreased, leaf width did not change significantly, the fresh weight and dry weight decreased gradually; under the same concentration of Cd2+, with the extension of growth period, the plant height, leaf width and fresh and dry weight increased gradually, but the leaf width, fresh and dry weight of Hybrid Pennisetum show bigger.(2) With Cd2+concentration increased the soluble sugar content, cell membrane permeability and proline content in leaves of both Pennisetums show increased tendency. Two varieties of Pennisetum in high concentration of Cd2+treatment (100 mg·kg-1) compare to the control (0 mg·kg-1) showed significant (.P<0.05) stress response; with extension of growth period, cell membrane permeability delivery increased by a wide margin; proline content was gradually decreased and that of the hybrid pennisetum decreased greatly; in the tillering stage soluble sugar content of Cd100, Cd75 treatment groups compare to other treatment groups was significant. With the increase of concentration of Cd2+ applied, malondialdehyde content increased gradually in both pennisetum, indicating that lipid peroxidation of cell membrane increased; ascorbic acid content decreased gradually and when the concentration of Cd2+was 100 mg·kg-1 showed most significant difference(P<0.05); the activity of enzyme active oxygen scavenging system including superoxide dismutase(SOD), peroxidase(POD), catalase(CAT) and glutathione peroxidase(GSH-PX), the enhanced activities of these enzymes can reduce the damage of membrane lipid peroxidation caused by Cd stress. Low Cd2+ concentration and control by comparison showed no significant difference(P>0.05), which indicated that Pennisetum of low concentration Cd stress had a certain stress reaction; while high concentration stress treatment compared with control was significant(P<0.05) and the four enzymes did not deactivate, indicating that the high concentration of Cd stress can do much more damage to the plant but did not destroy the system in Pennisetum, so as to further illustrate Pennisetum had good resistance to Cd stress. Two varieties of Pennisetum at different growth stages showed different stress degrees, overall performance in later growth stage show stronger than former period, indicating that the Cd stress time also caused some damage to the plant. Overall pearl millet showed stronger resistant ability than Hybrid pennisetum.(3) At the same growth stage, the content of chlorophyll a and chlorophyll b in pearl millet were higher than those of hybrid pennisetum; when the Cd concentration was 5 mg·kg-1, it showed little effect on net photosynthetic rate, transpiration rate, intercellular CO2 concentration, but with increasing of Cd2+ concentration, compared with the control the treatments decreased significantly, which hybrid pennisetum changed obvious indicated that high concentrations of Cd2+ treatment significantly affected the photosynthesis Pennisetum.(4) Root was the main Cd enrichment site and in three growth stages Pearl millet at Cd5 transfer factor were 12%,21%,44%, the bioconcentration factor were 47%,43% and 37%; in Hybrid pennisetum transfer factor were 12%,10%,76% enrichment factor was 55%,54%,69%, the content of Cd in seedling plants of three stages was highest showed it was most vulnerable to cadmium stress. Hybrid pennisetum showed stronger ability about repairing Cd contaminated soil and Pennisetum in lower concentration of Cd (<1.0 mg·kg-1) could still be as forage edible safety.(5) Cd stress will affect the crude protein content of two Pennisetum, Pearl millet firstly showed increased and then decreased. Hybrid pennisetum overall rise; crude fat content in different treatments were different but showed no significant difference with the control; when the Cd2+ concentration was 100 mg·kg-1, acid detergent fiber content was less than that of the control; also neutral detergent fiber content of Pearl millet was only Cd100 treatment less than the control, Hybrid pennisetum at each concentration treatment was higher than that of the control but showed not significant; crude ash in two kinds of Pennisetum among different treatments were different but also showed no significant. |
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