Reaserch Of Seed Germination, Plant Growth And Physiology Of Hemp Varieties Under Heavy Metal Pb Stress

Along with the development of industry and agriculture and the advancement of urban construction, environmental pollution has become a worldwide problem, while soil heavy metal contamination is one of environmental problems people concerned. At present, phytoremediation is the most prospected strategy to improve soil heavy metal contamination. Hemp (Cannabis sativa L.), an annual herbaceous fiber plant, with very high yield of biomass, strong resistance to adverse environments and high economic value, has been listed as a good candidate for phytoremediation of soil heavy metal contamination. Due to the diversity of hemp varieties and their differences in biological natures, the knowledge of hemp tolerance to heavy metals and plant accumulation of heavy metals in hemp varieties at different growth stages is far not comprehensive.In order to investigate Pb tolerance limits of hemp and understand the responses of growth and physiology during germination and seedling growth, the role of hemp in remediation of soil Pb contamination, seven hemp varieties were treated under different concentration of Pb solutions using paper culture and pot culture. The main results were as follows:1. Effects of Pb stress on germination and Pb tolerance evaluation in seven hemp varieties (Y1, Y5, B, Y6, W1,Q1, J1).(1) With the increasing of Pb concentration, the germination potential of 7 hemp varieties were not significantly different with the control, the germination rate of Y5 and Y6 increased, but other 5 varieties had similar trends as the control.(2) The lengths of root gradually shorten with the aggrandizing of Pb content, and were less than 1cm under the concentration of 1200mg/L Pb2+, which indicated that the root growth was seriously inhibited by Pb stress. The results also showed that the bud growth of Y6 and Q1 were promoted at low concentrations of Pb2+ and inhibited at high concentrations. The bud lengths of Y6 and Q1 were obviously higher than the control, with the length of 5.87cm and 7.15cm under the concentration of 150mg/L Pb2+, respectively. However, the lengthes of other 5 varieties showed decreasing trend.(3) By subordinate function methods, Pb tolerance evaludtion of hemp varieties at 600mg/L Pb2+were that BM, Y5, Q1 and Y6 were high tolerance, W1 and Y1 were middle tolerance, J1 was low tolerance.2. Effects of Pb stress on seedling growth of two hemp varieties (B and Y1).(1) Compared with the control, there were no significant differences in sprouting rate and stem diameter of two hemp varieties on Pb stress. With the increasing of Pb concentration, seeding height increased firstly and then decreased, but the lowest plant height was at 3500mg/kg Pb2+. The symptoms of Pb toxicity did not appear on plant morphology.(2) Under Pb stress, chlorophyll contents of Yl were higher than the control, but BM was opposite. Relative conductivity of hemp leaves were higher than the control, and the trend increased firstly and then decreased. With the increasing of Pb concentration, MDA contents and soluble sugar contents were increased in Yl leaves, but BM increased firstly and then declined. SOD activities and total protein contents of 2 hemp varieties leaves decreased with the increasing of Pb concentration.(3) Dry matter accumulation of stems and leaves of 2 hemp varieties increased firstly and then decreased, but the lowest was at 3500mg/kg Pb2+. Compared with BM, the effect of Pb stress on the dry weight of Y1 was more obvious.(4) Accumulation characteristics of Pb in hemp plant:The content of Pb in nutrition organs was in the order:root>shoot>leaf. The contents of Pb in hemp were less than 50 mg/kg, biological concentration factor (BCF) was less than 0.03, and transport factor (TF) was less than 0.6. Therefore, hemp was not the Pb enrichment plant. However, the Pb resistance coefficient (RC) of hemp was between 0.8 and 1.4, which indicated that hemp had a high tolerance to Pb stress. The results also showed that Pb tolerance ability of BM was higher than Y1. That meaned BM has higher potential in remediating soils contaminated by Pb.