Laguerre G, Courde L, Nouaïm R, Lamy I, Revellin C, Breuil M C, Chaussod R
INRA-Université de Bourgogne UMR Microbiologie et Géochimie des Sols, CMSE, 17 rue Sully, BP 86510, 21065 Dijon, Cedex, France.
Microb Ecol. 2006 Oct;52(3):426-35. doi: 10.1007/s00248-006-9081-5. Epub 2006 Aug 8.
The use of pesticides in agricultural soils may affect the soil microbiota. The effect of repeated application of copper sulfate in soil on indigenous populations of rhizobia was assessed in a medium-term field experiment. Copper sulfate was applied over 8 years at two different rates, 12.5 and 50 kg of CuSO4 ha(-1) year(-1), in the field. The concentrations of total copper in soil varied between 14.0 (control plots that did not receive copper sulfate) and 91.0 mg kg(-1) (the most contaminated plots) at the time of sampling, 3 years after the end of the copper treatments. All the other physicochemical parameters were similar among the plots that also shared the same cropping history. The target rhizobia were monospecific populations of Rhizobium leguminosarum bv. viciae nodulating Vicia sativa and communities of rhizobial species nodulating Phaseolus vulgaris. The size of the vetch rhizobial populations was significantly reduced in the soils with the higher Cu content, whereas the size of the Phaseolus rhizobial populations was not significantly affected. However, the number of nodules formed on both vetches and common beans were reduced for the plants grown in the most contaminated soils, suggesting an additional toxic effect of copper on plant physiology. The diversity (Simpson's indices) of rhizobial genotypes, as characterized by polymerase chain reaction restriction fragment length polymorphism of 16S-23S rDNA intergenic spacer (IGS), was not influenced by copper application. Also, the genetic structure of the R. leguminosarum bv. viciae populations was not modified by copper treatments. By contrast, a shift was observed in the composition of the Phaseolus-nodulating communities in relation to soil copper content. The communities were composed of three 16S rDNA haplotypes: one corresponding to the R. leguminosarum (biovar phaseoli) species, the two others forming a new lineage of Phaseolus rhizobia based on 16S rDNA sequence analysis. The reduced frequency of the R. leguminosarum species in the Phaseolus-nodulating communities from the copper-treated soils was linked to its higher sensitivity to copper as compared to the higher tolerance of isolates belonging to the other rhizobial lineage. The new lineage was functionally efficient for symbiotic nitrogen fixation with P. vulgaris. Our results suggest that functional redundancy among species exhibiting variability for copper tolerance preserved the size of Phaseolus-nodulating communities. In contrast, the abundance of the vetch-nodulating rhizobia, which was a monospecific functional group mainly constituted by copper-sensitive genotypes, was adversely affected by repeated application of copper sulfate.
在农业土壤中使用农药可能会影响土壤微生物群。在一项中期田间试验中，评估了在土壤中重复施用硫酸铜对根瘤菌土著种群的影响。在田间以两种不同的施用量，即每年每公顷12.5千克和50千克硫酸铜，连续8年施用硫酸铜。在结束铜处理3年后采样时，土壤中总铜的浓度在14.0（未施用硫酸铜的对照地块）至91.0毫克/千克（污染最严重的地块）之间变化。所有其他物理化学参数在具有相同种植历史的地块之间相似。目标根瘤菌是豌豆根瘤菌蚕豆生物型的单特异性种群，可使紫花苜蓿结瘤，以及可使菜豆结瘤的根瘤菌物种群落。在铜含量较高的土壤中，紫云英根瘤菌种群的规模显著减小，而菜豆根瘤菌种群的规模未受到显著影响。然而，在污染最严重土壤中生长的植物上，紫云英和普通菜豆上形成的根瘤数量均减少，这表明铜对植物生理有额外的毒性作用。通过16S - 23S rDNA间隔区（IGS）的聚合酶链反应 - 限制性片段长度多态性表征的根瘤菌基因型多样性（辛普森指数）不受铜施用的影响。此外，豌豆根瘤菌蚕豆生物型种群的遗传结构也未因铜处理而改变。相比之下，可以观察到与土壤铜含量相关的菜豆结瘤群落组成发生了变化。这些群落由三种16S rDNA单倍型组成：一种对应于豌豆根瘤菌（菜豆生物型）物种，另外两种基于16S rDNA序列分析形成了菜豆根瘤菌的一个新谱系。与属于其他根瘤菌谱系的分离株具有更高的耐受性相比，来自铜处理土壤的菜豆结瘤群落中豌豆根瘤菌物种的频率降低与其对铜的更高敏感性有关。这个新谱系在与菜豆共生固氮方面功能高效。我们的结果表明，在对铜耐受性表现出变异性的物种之间的功能冗余保持了菜豆结瘤群落的规模。相比之下，紫云英结瘤根瘤菌的丰度，这是一个主要由对铜敏感的基因型组成的单特异性功能组，受到重复施用硫酸铜的不利影响。
