Studies On Remediating The Cd Contaminated Soil By Nursery Stock

A serious of field and pot-experiments with 20 nursery stock species subjected to different cadmium (Cd) exposure were conducted to investigate their patterns of Cd accumulation and tolerance. Meanwhile, their transplanting potentials were also studied for remediation of Cd-contaminated soil. Furthermore, we amended silicon and alum plasma as chemical stablizers to Cd-contaminated soil to strengthen the remediation effect of the studied nursery stock species. The main results were shown as follows: The screening work of nursery stocks as aspect of their Cd tolerance potentials were conduceted by two experiments during two-studied years.1,The first screening nursery stocksIn the first-year experiment, the sceening work was carried out with seven nursery stocks treated with 50, 100 and 200 mg·kg-1 Cd for 84 days. Furthermore, the risk of Cd-release from transplanted plant was also studied by determination of Cd concentration in rhizosphere and bulk soil of transplants, and by comparison of total Cd content between before and after transplanting for 120 days.In different Cd concentrations, the plant growth conditions of seven nursery stocks showed different degrees of poisoning. Under 50 mg·kg-1 Cd, the main mitigate effect were in roots rather than stems and leaves, while the biomass of stems and leaves decreased much greater than root in the presence of 100 or 200 mg·kg-1Cd.Epidermis of roots of all species hold much more Cd than that in cortex with stele, and the highest ratio of Cd concentration between epidermis and cortex with stele was found in B.I. Cupressus. In 50 mg·kg-1 Cd treatment, the highest total Cd content was noted in T.A. Pittosporum(12.74‰), followed by J. Euonymus and B.I. Cupressus. While in 100 and 200 mg·kg-1 treatments, the highest relative uptake was B.I. Cupressus, which were 15.1‰and 13.64‰. Three species, namely J. Euonymus, T.A. Pittosporum and B.I. Cupressus, withstanded 50 mg·kg-1 Cd stress, according to no significant difference in total biomass between the controls and the Cd-stressed plants, and B.I. Cupressu was even grown well in 100 mg·kg-1 Cd contaminated soil.Through screening, J. Euonymus, T.A. Pittosporum and B.I. Cupressus have better resistance to Cd ability and high Cd accumulating quantity in 50 mg·kg-1 Cd treatment. Recommend them as Cd pollution soil phyto-remediation woody plants. T.A. Pittosporum was suitable for moderate Cd pollution plant fixed (less than 50 mg·kg-1 Cd). B.I. Cupressus for used for serious Cd pollution (more than 100 mg·kg-1).2,The second screening nursery stocksIn the second experiment, 13 nursery stocks exposed to 100 mg·kg-1 Cd were further tested during 30-day grown period. Results showed that: the increases in heights of 13 species nursery stock were all lower than that of control, which showed Cd inhibiting effect of plant growth. Cd were mainly found in roots among the 13 studied plants,however, Ternstroemia gymnanthera and Camellia sasanqua accumulated very low Cd and their Cd concentrations of shoots and roots were both less than 0.2 mg·plant-1. In 100 mg·kg-1 Cd treatment soil, Cd concentrations in rhizosphere were lower than in bulk soil, which indicated plant adsopted much Cd from soil. It concluded that as Cd-toletant plant, Ternstroemia gymnanthera and Camellia sasanqua could be used for remediation of low level Cd-contaminated soil.3,Risk analysis of Cd release of transplanting seedlingsAfter transplanting J. Euonymus, T.A. Pittosporum and B.I. Cupressus for 120 days, some Cd in roots were transferred into shoots, and some Cd were released into soil. There was no significant difference in Cd concentrations of bulk soil compared to that of rhizosphere in 50 mg·kg-1 treatment. Cd concentration in bulk soil were increased in 100 and 200 mg·kg-1 Cd treatments. The highest Cd concentrations (0.43 mg·kg-1) in bulk soil were found in T.A. Pittosporum in the presence of 200 mg·kg-1 Cd, which was much lower than Environmental quality standard for soils in China (1 mg·kg-1). Thus, it is affirmed by our study that the new approach can be safely implemented for remediation heavy metal-polluted soil.4,The research on the effects of exogenous silicon mediated on the growth and soil Cd forms in nursery stock showed that Cd-induced inhibition on the growth of the two Cypress species was mitigated in the presence of Si 100 mg·kg-1soil. Whether the existing Cd pollution of soil or not, effect of Si 100 mg·kg-1 treatment on the growth of two Cypress species have the obvious positive effect compared to no Si treatment. Two Cypress species showed two contrary trend in Cd absorption. Adding Si 100 mg·kg-1 was good for roots, stems, leaves of Platycladus orientalis on Cd absorption, but reduces the Juniperus chinensis roots, stems, leaves on Cd absorption.For physiological and biochemical indexes, under Cd stress the activities of POD and CAT increased while the activities of SOD decreased, which indicated that the the plants' resistance were improved by amendment of Si. MDA content of two plant speices in 100 mg·kg-1 Si treatment is lower than no Si treatment, which indicated the oxidant tress were induced by Cd were mitigated by Si. Under Si treatment Cypress showed a substantial tolerance to Cd stress.The results of the effects of alum plasma on the form of soil Cd, the growth of Photinia serrulata and the Cd absorption shown that with the increase of alum plasma, dry weight of Photinia serrulata showed increase trend, while Cd content of roots, stems, leaves decreased. Dry weigh is the biggest in 2.5% of Photinia serrulata treatment. The best effct of Cd adsorption is alum plasma modificated by hot alkali which specific surface increased one time. With the increase of alum plasma proportion, the soil pH showed increase trend. In the 2.5% treatment, Photinia serrulata absorbed less Cd and grew better. So 2.5% treatment could be served as the reasonable proportion.5,The conduction of demonstration field on heavy metal pollution soil of phyto-remediation in Yin shan mine, Shang yu.The test field was located on northern 300 meters of Yin shan mine. It has established near an area of 2 acres. The plant screened in the above study out resistance to fight Cd type seedlings: Juniperus chinensis , Platycladus orientalis, J. Euonymus and T.A. Pittosporum in 6.25, 2010. J. Euonymus and T.A. Pittosporum were for the first seedling which have Cd strong resistance; Juniperus chinensis and Platycladus orientalis is mining area common plants. At present, these plants are growing in the region, waiting for further promoting the new technology.