Effects Of Drought And Lead Stress On Seed Germination And Seedling Growth Of Main Tree Species For Afforestation

In order to research the effect of different Lead compounds, different drought stress,drought and Lead interactive stress on major afforestion tree species seed germination andseedling growth, with the full and the same size seeds of Platycladus orientalis, Pinustabuliformi, Pinus armandii, Mongolica litv, Robinia psedoacacia, Koelreuteria paniculata,Gleditsia horrida, Ailanthus altissima, Pyrus betulaefolia, Amaorpha fruticosa, Lespedezabicolor, Hippophae rhamnoides as material, an indoor seed germination experiment wasconducted respectively in simulating different drought stress(the soil relative water content:100%,80%,65%,60%,55%,40%, the concentration of PEG6000:0%,9.5%,20%,30%,35%,40%), different Lead compounds stress(Lead nitrate: Pb content with0,0.3,0.5,1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0g/kg, Lead acetate: Pb content with0,0.3,0.5,1.0,2.0,3.0,4.0、5.0,6.0,7.0,8.0,9.0,10.0,11.0,12.0,13.0,14.0,15.0g/kg), drought and Lead interactivestress (the soil relative water content with100%,80％,65％,55％,40％, Pb content with0,0.3,1.0,2.0,4.0,6.0g/kg)to measure the change of the rates of seed germination, vigor index,root and stem elongation, and weight of seedlings. It could help to select vegetationrestoration tree species to Lead polluted soil in arid and semiarid areas, evaluate the differentecological effects of different Lead compounds and different drought stress on forest treeseeds. The main results were summarized as follows:1．The effect of Lead nitrate on rates of seed germination, vigor index, root and stemelongation, and weight of seedlings for twelve plants was obvious, Low levels of Lead nitrate(0.3g/kg-0.5g/kg) could promote the sprouting of the seeds and the growth of the seedlings,but high levels of Lead nitrate (0.5-10.0g/kg)would inhibit the sprouting of the seeds and thegrowth of the seedlings. The resistance of twelve forest tree seeds was evaluated by principalcomponents analysis and subordinate function analysis,the sequence of Lead nitrate resistanceof twelve seeds from strong to weak was Amaorpha fruticosa＞Platycladus orientalis＞Koelreuteria paniculata＞Gleditsia horrida＞Robinia psedoacacia＞Pinus tabuliformis＞Pyrus betulaefolia＞Lespedeza bicolor＞Mongolica litv＞Hippophae rhamnoides＞Ailanthusaltissima＞Pinus armandii, Amaorpha fruticosa, Gleditsia horrida, Platycladus orientalisand Koelreuteria paniculata could be used as patient plants to the phytoremediation of Leadnitrate polluted soil. Hippophae rhamnoides, Pinus armandii and Mongolica Litv could be applicated as indicative plant to diagnose the toxicity of Lead nitrate on soil weight.2. The effect of Lead acetate on rates of seed germination, vigor index, root and stemelongation, and weight of seedlings for twelve seeds was obvious, low levels of Lead acetate(0.3g/kg-4.0g/kg) could promote the sprouting of the seeds and the growth of the seedlings,but high levels of Lead acetate (4.0-15.0g/kg)would inhibit the sprouting of the seeds and thegrowth of the seedlings. The resistance of six forest tree seeds was evaluated by principalcomponents analysis and subordinate function analysis,the sequence of Lead acetateresistance of six seeds from strong to weak was Amaorpha fruticosa＞Platycladus orientalis＞Pinus tabuliformis＞Koelreuteria panicula＞Amaorpha fruticosa＞Hippophae rhamnoidestherefore, Amaorpha fruticosa and Platycladus orientalis could be used as patient plants tothe phytoremediation of Lead acetate polluted soil, Hippophae rhamnoides could beapplicated as indicative plant to diagnose the toxicity of Lead pollution on soil weight.3. The inhibition effect order of Lead nitrate and Lead acetate to the growth index ofthese forest tree seeds was same：root length, vigor index, stem length, germination, weight.These forest tree seeds responded differently to two kinds of Lead compounds due to its owncharacteristics, seeds were more sensitive to Lead nitrate than Lead acetate.4. The effect of soil relative water content and PEG6000on rate of seeds germination,vigor index, root and stem elongation, and weight of seedlings for twelve seeds was different.When the water potential was in the range of-0.3～-1.0MPa, PEG simulation method couldwell simulate drought stress, while the rate of germination and root length could not besupposed as the evaluation index of drought stress. But when the water potential was below-1.5MPa, there was a great deviation of the growth index between PEG simulation methodand the actual soil drought stress.5. The effect of soil relative water content and Lead stress on the seed germination andseedling growth for Amaorpha fruticosa and Hippophae rhamnoides was great. Mild waterdeficit (the soil relative water content was80%-65%) and Mild Lead stress (the Lead contentin soil was0.3-1.0g/kg) could promote the rate of seed germination and seedling growth forAmaorpha fruticosa and Hippophae rhamnoides, but with the severity of drought stress andLead stress increased, it would inhibit the sprouting of the seeds and the growth of theseedlings. When the soil relative water content was40%, the decreasing amplitude of everyindex of seed germination and seedling growth for Amaorpha fruticosa and Hippophaerhamnoides were the greatest, with the severity of drought stress increased, the inhibition ofLead stress to seed germination and seedling growth was abated.