ISSN:
1435-0661
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
Notes:
2+ and Cd2+ activities on white clover (Trifolim repens L.), Rhizobium leguminosarum bv. trifolii, the infection process, and nodulation, a growth chamber study was conducted. The chelator EGTA [ethylenebis (oxyethylenetrinitrilo) tetraacetate] was used to buffer Zn2+ and Cd2+ activities in nutrient solution from pZn2+ = 8.0 to 5.0 and pCd2+ = 10.5 to 8.0 mol L-1. Plants grown in pZn2+ = 5.0 and pCd2+ = 8.75 and 8.65 were stunted and chlorotic with interveinal necrosis. Shoot concentrations of Zn and Cd averaged 〉200 and 40 mg kg-1, respectively, in these treatments. This resulted in a 60% yield reduction for plants grown in pZn2+ = 5.0. In pCd2+ = 8.75 and 8.65, 40 and 60% yield reductions, respectively, were observed. In treatments where mineral N was supplied to plants, 20 to 35% greater shoot yield was recorded compared with plants inoculated with rhizobia, presumably due to a period of starvation for N due to the delay in the onset of fixation. Nodulation was observed at all Zn2+ and Cd2+ activities. At pCd2+ = 8.75 and 8.65, however, there was a delay in nodulation. Most nodules were effective in N2 fixation irrespective of Zn2+ and Cd2+ activity. Enumeration of viable cells showed a significant decline of total cell counts from 105.5 cells mL-1 in the control to 105.0 and 104.5 cells mL-1 at the highest Zn2+ and Cd2+ activities, respectively. At the activities studied, Cd was more toxic to rhizobia and nodulation than Zn. At the highest Cd2+ activity, however, plants were killed within 48 h due to metal toxicity. This technique showed for the first time that toxicity of Zn and Cd was greater to plants than to rhizobia.
Type of Medium:
Electronic Resource
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