Abstract: A hydroponic experiment was conducted to study the effects of different concentration (CK, 5, 10, 15, 20, and 25 μmol·L-1) Cu in nutrient solution on the growth of Astragalus sinicus. At 5 μmol·L-1 of Cu, the under- and aboveground biomass of A. sinicus increased significantly, plant height had an increase, and nodules were mostly in pink, tended to be complex, heaped up, and bigger than the control. At 10 μmol·L-1 of Cu, the underground biomass still increased significantly, plant height had a larger increment than the control, but aboveground biomass had no significant increase, and root growth was inhibited and root length was shortened significantly. At 15 μmol·L-1 of Cu, an early manifestation of plant damage was observed, the root turned from white to brown, leaf turned from green to yellow, nodule number decreased, and under- and aboveground dry mass as well as branch number decreased significantly. When the Cu concentration reached to above 20 μmol·L-1, the plant was shortened noticeably, and the growth indicators including root length, root fresh mass and dry mass, branch number, stem length, and aboveground fresh mass and dry mass all decreased greatly. Observation under optical and transmission electron microscopes showed that the Cu-contaminated leaves were thickened, with the expansion of leaf cell and the incrassation of palisade tissues. The yellow leaves might result from the damage to chloroplasts. Cortical cell death in root system might also have a negative effect on root water absorption and transportation, causing plant water content decreased.

Key words: Cucumber, Rhizosphere, Pathogen, Antagonistic bacteria, Population number