ABSTRACT New Zealand pastoral productivity relies heavily on biological nitrogen (N) fixation from rhizobia bacteria. Cadmium (Cd), present in pasture soils as an impurity in phosphate fertilisers, may have toxic effects on both plant growth and rhizobia activity. Effects of Cd on growth of seedlings of a white clover cultivar ‘Grasslands Tribute’, in the absence and presence of the N2-fixing Rhizobium leguminosarum bv. trifolii strain TA1, were assessed in vermiculite microcosm assays. The lowest observable effect concentrations resulting in significantly lower white clover shoot weights than those grown without Cd were 0.07 mg Cd kg−1 (measured as Ca(NO3)2-extractable Cd, Cdextractable) in the absence of Rhizobium, and 2.33 mg Cdextractable kg−1 for Rhizobium-inoculated seedlings. Shoot N content was unaffected in white clover exposed to <5 mg Cdextractable kg−1. The results indicate symbiosis with Rhizobium strain TA1 conferred tolerance to white clover ‘Grasslands Tribute’ against Cd toxicity, and that this symbiosis is unlikely to be adversely affected by Cd concentrations reported (<0.003 mg Cdextractable kg−1) in New Zealand pasture soils.

中文翻译：

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Rhizobium leguminosarum bv. 之间的共生关系。三叶草菌株 TA1 和白三叶草栽培品种有利于三叶草对镉毒性的耐受性

摘要新西兰的牧区生产力在很大程度上依赖于根瘤菌的生物固氮（N）。镉 (Cd) 作为磷酸盐肥料中的杂质存在于牧场土壤中，可能对植物生长和根瘤菌活动产生毒性影响。在不存在和存在固氮根瘤菌 bv 的情况下，Cd 对白三叶草品种“Grasslands Tribute”幼苗生长的影响。trifolii 菌株 TA1，在蛭石微观分析中进行了评估。在没有根瘤菌的情况下，导致白三叶草枝条重量显着降低的最低可观察浓度为 0.07 mg Cd kg-1（测量为 Ca(NO3)2-可提取的 Cd，Cdextractable）和 2.33 mg Cdexttractable kg -1 用于接种根瘤菌的幼苗。暴露于<的白三叶草的芽N含量不受影响 5 mg Cdextractable kg-1。结果表明，与根瘤菌 TA1 菌株的共生赋予了对白三叶草“Grasslands Tribute”抗镉毒性的耐受性，并且这种共生不太可能受到新西兰牧场土壤中报告的镉浓度（<0.003 毫克 Cdextractable kg-1）的不利影响。