contaminated soils. The results from this study indicate that the plant exhibited high tolerance to Cu toxicity in the soils, and normal growth was attained up to 80mgkg-1 available soil Cu (the NH4OAc extractable Cu) or 1000mg kg-1 total Cu. Under the field conditions, a biomass yield of 9 ton ha-1 was recorded at the soil available Cu level of 77mg kg-1, as estimated by the NH4OAc extraction method. Concentration-dependent uptake of Cu by the plant occurred mainly at the early growth stage, and at the late stage, there is no difference in shoot Cu concentrations grown at different extractable soil Cu levels. The extractability of Cu from the highly polluted soil is much greater by the roots than that by the shoots. The NH4OAc extractable Cu level in the polluted soil was reduced from 78 to 55mgkg-1 in the soil after phytoextraction and removal of Cu by the plant species for one growth season. The depletion of extractable Cu level in the rhizosphere was noted grown in the mined area, even at high Cu levels, the NH4OAc extractable Cu in the rhizosphere was 30% lower than that in the bulk soil. These results indicate that phytoextraction of E. splendens can effectively reduce the plant-available Cu level in the polluted soils.

rmined for Chinese cabbage (Brassica chinensis L.), pakchoi (Brassica chinensis L.), and celery (Apiumg graveolens L.). Different Zn levels (0, 100, 200, 300, 400mg kg21 soil, supplied as ZnSO4•7H2O) were added to the soil samples, based on Zn adsorption-desorption characteristics of the soil, the availability of added Zn in the soil decreased with time, with minimal change after 10-12 weeks of incubation. The results from sand and soil culture experiments showed that shoot growth was significantly inhibited at Zn concentrations above 25mg L21 in nutrient solution or at DTPA-Zn above 170mg kg21 in the soil. The sensitivity to Zn toxicity differed among the three vegetable crops, changing in the order: celery . Chinese cabbage. pakchoi. Zinc concentration in shoots and edible parts varied with Zn supply levels and type of the vegetables. Negative correlations were noted between Zn concentrations in shoots and dry matter yields (r=0.90-0.98, P, 0.01), the critical Zn concentrations in plant tissues at 10% reduction of biomass yield (PT10) were 173.1, 167.5, 144.2 and 222.2mg kg21 (DW) for Chinese cabbage, pakchoi, celery (stem) and celery (leaf), respectively. Zinc concentrations in the edible parts were positively correlated with available and total Zn in the soil (r=0.91-0.99, P, 0.01). Based on the threshold of human dietary toxicity for Zn (20mg kg21), the critical concentrations of total and available Zn in the soil were 413 and 244mg kg21 for Chinese cabbage, 224 and 75mg kg21 for pakchoi, and 272 and 101mg kg21 for celery, respectively. These results indicate that some vegetable species like pakchoi might accumulate Zn in edible parts over human dietary toxic threshold before the dry matter yield reduction was observed.

Information on phosphorus (P)-solubilizing microorganisms in variable charge soil is lacking. We screened soil microorganisms that can effectively utilize P adsorbed on variable charge minerals using a series of synthetic media of decreased P availability. Rhizospheric soil (Orthic plintaqualt) from a 30-y old tea plant was diluted and aseptically inoculated to a series of media containing P adsorbed on goethite at 0, 255, 50, 75, and 100% saturation. Microorganisms, which survived in the 25% P sorption saturation medium, were each by colony isolates transferred to another freshly prepared medium of the same type for growth stability test. Microbial species, which could grow and reproduce for more than 15 generations in the 25% P-saturation medium were considered as P-solubilizing microbes (PSMs) and used for identification tests. By this procedure, we screened one PSM population which was identified as the bacterium Moraxella sp by Gram staining, Gamma culture and staining, optical and electron microscopic observation, and enzyme-oxidizing reaction. The PSMs have higher maximal transport rates to P than the ubiquitous soil microorganisms and have an optimal temperature of 378C and optimal pH of 5.5-7.5 for growth.