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首页> 外文期刊>Plant and Soil >A study of the impacts of Zn and Cu on two rhizobial species in soils of along-term field experiment
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A study of the impacts of Zn and Cu on two rhizobial species in soils of along-term field experiment

机译：锌和铜对土壤中两种根瘤菌物种的影响的长期田间试验研究

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摘要

Two agriculturally important species of rhizobia, Rhizobium leguminosarum biovar viciae (pea rhizobia) and R. leguminosarum bv. trifolii (white clover rhizobia), were enumerated in soils of a long-term field experiment to which sewage sludges contaminated predominantly with Zn or Cu, or Zn plus Cu, were added in the past. In addition to total soil Zn and Cu concentrations, soil pore water soluble Zn and free Zn2+, and soluble Cu concentrations are reported. Pea and white clover rhizobia were greatly reduced in soils containing greater than or equal to 200 mg Zn kg(-1), and soil pore water soluble Zn and free Zn2+ concentrations greater than or equal to 7 and greater than or equal to 3 mg l(-1), respectively, in soils of pH 5.9-6. Copper also reduced rhizobial numbers, but only at high total soil concentrations (> 250 mg kg(-1)) and not to the same extent as Zn. Yields of field grown peas decreased significantly as total soil Zn, soil pore water soluble Zn and free Zn+2 increased (R-2 = 0.79, 0.75 and 0.75, respectively; P < 0.001). A 50% reduction in seed yield occurred at a total soil Zn concentration of about 290 mg kg(-1), in soils of pH 5.9-6. The corresponding soil pore water soluble Zn and free Zn2+ concentrations were about 9 and 4 mg l(-1), respectively. Pea seed yields were not significantly correlated with total soil Cu (R-2 = 0.33) or soil pore water soluble Cu (R-2 = 0.39). Yield reductions were due to a combination of greatly reduced numbers of free-living rhizobia in the soil due to Zn toxicity, thus indirectly affecting N-2-fixation, and Zn phytotoxicity. These effects were exacerbated in slightly acidic soils due to increased solubility of Zn, and to some extent Cu, and an increase in the free Zn2+ fraction in soil pore water. The current United Kingdom, German and United States limits for Zn and Cu in soils are discussed in view of the current study. None of these limits are based on toxicity thresholds in soil pore water, which may have wider validity for different soil types and at different pH values than total soil concentrations.
机译：根瘤菌的两个农业重要物种，豆科根瘤菌（豌豆根瘤菌）和豆科根瘤菌。在长期的田间试验的土壤中列举了三叶草（白三叶草的根瘤菌），过去曾在其中添加了主要被Zn或Cu或Zn加Cu污染的污水污泥。除了土壤中锌和铜的总浓度外，还报告了土壤孔隙中水溶性锌和游离Zn2 +以及可溶性铜的浓度。大于或等于200 mg Zn kg（-1）的土壤和土壤孔隙中水溶性锌和游离Zn2 +的浓度大于或等于7且大于或等于3 mg l时，豌豆和白三叶草的根瘤菌大大减少（-1）分别在pH值为5.9-6的土壤中。铜也减少了根瘤菌数量，但仅在土壤总浓度较高时（> 250 mg kg（-1）），而与锌的程度不同。随着土壤总锌，土壤孔隙水可溶性锌和游离锌+2的增加，豌豆的产量显着下降（R-2分别为0.79、0.75和0.75; P <0.001）。在pH值为5.9-6的土壤中，土壤总Zn浓度约为290 mg kg（-1）时，种子产量降低了50％。相应的土壤孔隙水溶性锌和游离Zn2 +浓度分别约为9和4 mg l（-1）。豌豆种子的产量与土壤总铜（R-2 = 0.33）或土壤孔隙水溶性铜（R-2 = 0.39）没有显着相关。产量下降的原因是由于锌的毒性，土壤中的自由生根瘤菌数量大大减少，从而间接影响了N-2的固定和锌的植物毒性。由于增加了Zn的溶解度（在一定程度上增加了Cu的溶解度）以及增加了土壤孔隙水中游离Zn2 +的比例，这些影响在弱酸性土壤中更加严重。鉴于当前的研究，讨论了英国，德国和美国目前土壤中锌和铜的限量。这些限制均不基于土壤孔隙水中的毒性阈值，对于不同的土壤类型和不同的pH值，其毒性阈值可能比总土壤浓度具有更大的有效性。

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