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Zinc and Cadmium Effects on Rhizobia and White Clover using Chelator‐Buffered Nutrient Solution
Author(s) -
Ibekwe A. M.,
Angle J. S.,
Chaney R. L.,
Berkum P.
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200010027x
Subject(s) - rhizobia , shoot , cadmium , nutrient , inoculation , rhizobium leguminosarum , zinc , trifolium repens , chelation , chlorosis , horticulture , biology , botany , chemistry , nitrogen fixation , symbiosis , rhizobiaceae , bacteria , organic chemistry , genetics , ecology
Toxicity of metals to plants and microbes depends on the chemical activities of metals in the soil solution. To examine the effects of Zn 2+ and Cd 2+ 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 Zn 2+ and Cd 2+ activities in nutrient solution from pZn 2+ = 8.0 to 5.0 and pCd 2+ = 10.5 to 8.0 mol L −1 . Plants grown in pZn 2+ = 5.0 and pCd 2+ = 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 pZn 2+ = 5.0. In pCd 2+ = 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 Zn 2+ and Cd 2+ activities. At pCd 2+ = 8.75 and 8.65, however, there was a delay in nodulation. Most nodules were effective in N 2 fixation irrespective of Zn 2+ and Cd 2+ activity. Enumeration of viable cells showed a significant decline of total cell counts from 10 5.5 cells mL −1 in the control to 10 5.0 and 10 4.5 cells mL −1 at the highest Zn 2+ and Cd 2+ activities, respectively. At the activities studied, Cd was more toxic to rhizobia and nodulation than Zn. At the highest Cd 2+ 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.