Study On Tolerance Screening And Accumulation Characteristics Of 10 Species Of Gramineae Ornamental Grasses Under Copper And Zinc Combined Stress

Rapid industrialization,modern agricultural production and other man-made activities have released a large amount of toxic heavy metals into the ecological environment,which has severely toxic effects on all forms of living organisms,and has changed soil characteristics and its biological activity.Remediating the contaminated sites has become a top priority for maintaining ecological balance and sustainable development.Among the many measures of remediation,phytoremediation is a low-cost,effective and environmentally friendly.The selection of hyperaccumulator or tolerant plants is the key to phytoremediation technology.Gramineae ornamental grass,as a plant with both ornamental and ecological value,is rich in species,highly resistant to stress,large in biomass,and low in management and maintenance costs.It has a broad prospect in the remediation of soil heavy metal pollution.In this study,ten kinds of Gramineae ornamental grasses were used as test material.According to the copper and zinc composite pollution standard,the upper and lower concentration thresholds were set,and then the seed germination test was used to analyze the differences in stress tolerance to seed germination characteristics and seedling growth of test plants.Potted plant control experiment was conducted to further explore the effects of stress on the growth status of the annual test plants,the response mechanism of the antioxidant system,and the accumulation and transport of copper and zinc in the plant.The purpose is to excavate and select plants with potential for remediation of heavy metal copper and zinc complex pollution,and to lay a foundation for the application of ornamental grasses in phytoremediation.The main findings are as follows:(1)During seed germination period,the germination characteristics of Muhlenbergia capillaris exhibited low-promotion and high-inhibition,germination rate,germination potential,germination index,vitality index,germ length,radicle length and seedling fresh weight of the remaining nine test plants all showed a downward trend with increasing stress concentration.In addition,radicle length of all tested plants was significantly greater than that of germ length and fresh weight of seedlings.Based on comprehensive evaluation and subordination function method,the tolerance of ten species of Gramineae ornamental grasses to copper and zinc combined stress in the germination period was in order of Pennisetum setaceum ‘Rubrum’>P.alopecuroides ‘Little Bunny’>Eragrostis elliotii>P.setaceum>M.capillaris>E.nutans>Cymbopogon citratus>M.sinensis ‘Gracillimus’ >M.sinensis‘Variegatus’ >M.sinensis ‘Zebrinus’.(2)With the increase of time and the rise of the mass concentration of the treatment solution,the growth status and morphological indicators of ten species of Gramineae ornamental grass potted plants showed a tendency of increased inhibit effects.Compared with the previous two months,the toxic effects of the test plants in the third month of stress were significantly intensified,and the growth status and plant status were the worst.Under the condition of the low concentration T1 stress,the growth status of the rest seven test plants were not good except for the good growth status of P.setaceum,P.setaceum ‘Rubrum’ and E.nutans.The toxic effects with different degrees appeared.With the continuous increase of the mass concentration of the treatment solution,under the condition of the high concentration T4 stress,except for the good growth status of E.nutans,the growth status of the rest test plants showed a large number of leaves had turning yellow,felled,wilted and even died phenomenons.(3)Under different concentrations of copper and zinc composite aqueous solutions,the response mechanism of the antioxidant system of test plants was different.Malondialdehyde content in leaves of all tested plants showed an increasing trend with the increase of stress concentration.Except for the activity of peroxidase in leaves of M.sinensis ‘Gracillimus’ and C.citratus,which increased first and then decreased,the activity of peroxidase in the leaves of other test plants gradually increased.Superoxide dismutase and catalase activities in the leaves of all tested plants showed a trend of first increase and then decrease when iron concentrations increased.(4)The differences of different test plants in the absorption,enrichment and transport capacity of copper and zinc were significant.In general,the enrichment and transport capacity of zinc in all tested plants was stronger than copper.Compared with the upper part of the ground,the absorption ability of the lower part of the ground plants to absorb copper was stronger.However,compared with the lower part of the ground,the absorption ability of the upper part of the plant to zinc was stronger.On the basic of the screening criteria for super-enriched plants,all test plants were not copper or zinc hyperaccumulator.The Q-type clustering analysis method was adopted,the ten species of Gramineae ornamental grasses potted plants could be divided into the following three categories when the relative distance is five.The first category was high copper and zinc accumulation type,including E.elliotii and M.sinensis‘Gracillimus’;the second category was medium copper and zinc accumulation type,there are M.sinensis,P.setaceum,M.capillaris,E.nutans and P.alopecuroides ‘Little Bunny’;the third category was low copper and zinc accumulation type,including C.citratus,P.setaceum‘Rubrum’ and M.sinensis ‘Variegatus’.(5)The tolerance and cumulative transport capacity of ten test plants to copper and zinc were comprehensively evaluated and analyzed.Within the range of the T2 concentration value,M.sinensis ‘Zebrinus’,P.setaceum and E.nutans can be used as the tolerant material for soil copper and zinc compound pollution and for stable phytoremediation,and M.sinensis ‘Variegatus’ can be used as the indicator material for soil copper and zinc compound pollution and for monitoring potential polluted area.