Influence of the Size of Indigenous Rhizobial Populations on Establishment and Symbiotic Performance of Introduced Rhizobia on Field-Grown Legumes

Thies, Janice E.; Singleton, Paul; Bohlool, B. Ben

doi:10.1128/aem.57.1.19-28.1991

Cited by 350 publications

(167 citation statements)

References 27 publications

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“…Likewise, studies on soybean and other agricultural legumes showed that an increasing number of rhizobia in the host rhizosphere can result in a linear increase in nodulation (Elegba & Rennie 1984;Patrick & Lowther 1995;Deaker, Roughley & Kennedy 2004). However, inoculation effects can be negatively influenced by indigenous rhizobial populations with high nodulation competitiveness (Singleton & Tavares 1986;Thies, Singleton & Bohlool 1991). Like for O. glaberrima (Table S1), phylogenetically diverse bacteria have been isolated from Acacia nodules.…”

Section: Discussionmentioning

confidence: 99%

Distance‐dependent effects of pathogenic fungi on seedlings of a legume tree: impaired nodule formation and identification of antagonistic rhizosphere bacteria

Liu

Xie

et al. 2016

Journal of Ecology

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1. The Janzen-Connell (JC) hypothesis proposes that diversity of tree communities is promoted by species-specific enemies that suppress seedling recruitment. Pathogenic soil-borne fungi are often responsible for JC effects. However, previous ecological studies have not placed JC effects in the context of beneficial soil bacteria. Using the JC effect surrounding a subtropical legume tree (Ormosia glaberrima) as a model, we characterized tripartite interactions between seedlings, soil fungi and plant-associated bacteria. 2. Survival of seedlings grown in soil inocula collected at close distances to focal adult trees was reduced. Half of the experimental units were treated with fungicides to confirm the presence of pathogenic fungi. In a parallel experiment, nitrogen-fixing rhizobia induced fewer nodules on O. glaberrima seedlings when soil inocula were collected closer to focal adult trees. An inoculation experiment with rhizobial isolates promoted nodulation of seedlings grown in soil taken at close distances to adult trees, suggesting that rhizobial densities are suboptimal at these locations. 3. Fusarium oxysporum, a pathogen of O. glaberrima seedlings, produced exudates that inhibited growth of most bacteria isolated from nodules. Accordingly, F. oxysporum negatively affected rhizosphere colonization of rhizobia in a co-inoculation experiment. Contrariwise, certain Burkholderia isolates (from nodules and the rhizosphere) were identified that possess the ability to inhibit growth of F. oxysporum. The majority of the antagonistic bacteria were isolated from locations with fungal pathogens, suggesting competition between fungi and rhizosphere bacteria. 4. Exclusion of pathogenic fungi by application of fungicides promoted nodulation of O. glaberrima seedlings under growth-room and field conditions. 5. Synthesis. Our findings indicate that soil-borne pathogens surrounding adult trees are microbial keystone species that locally influence interactions between seedlings and plant-associated bacteria.

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Section: Discussionmentioning

confidence: 99%

Distance‐dependent effects of pathogenic fungi on seedlings of a legume tree: impaired nodule formation and identification of antagonistic rhizosphere bacteria

Liu

Xie

et al. 2016

Journal of Ecology

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“…In the USA, where soybean is also an important crop, there are frequent reports of a lack of response to inoculation in soils with few cells of established bradyrhizobia [22,27]. Contrarily, in Brazil ¢eld responses to inoculation can be obtained even in soils with up to 10 5 cells of soybean bradyrhizobia g 31 of soil [9,10,12,13,17,28,32].…”

Section: Discussionmentioning

confidence: 99%

Characterization of soybean Bradyrhizobium strains adapted to the Brazilian savannas

Santos¹

1999

FEMS Microbiology Ecology

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Brazilian soils are originally free from soybean bradyrhizobia and the first inoculants were brought to the country in this century, but a search for adapted strains started immediately and still continues. A strain selection program was established at Embrapa based on the reisolation of strains after a long period of adaptation to the soils followed by a search for variant genotypes with higher N 2 fixation capacity and competitiveness. A second approach of this program consists of searching for variant colonies of a single strain with higher N 2 fixation rates and competitiveness, following a short period of adaptation to the soil. In this study, using both approaches, strains belonging to three serogroups, CB 1809, 532C and SEMIA 5020, were obtained. In general, the variant strains showed differences in colony morphology (mucoidy) but produced similar protein and lipopolysaccharide profiles. Within serogroup CB 1809, containing variants obtained via the second approach, a low level of DNA polymorphism was detected relative to the parental genotype by ERIC and REP-PCR. However, within the two other serogroups, containing variant strains obtained via the first approach, a high level of polymorphism in ERIC and REP-PCR fingerprints was observed relative to the putative serologically related parental genotypes. These results show that a great variability can be detected following adaptation of Bradyrhizobium strains to the soil, although other potential explanations for the DNA polymorphisms observed are discussed. Some of the variant strains obtained by both methodologies were found to have higher rates of N 2 fixation and almost all were more competitive than the parental genotypes, suggesting that it is possible to select variant strains which can contribute to an improved plant N nutrition status. ß

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“…First, additional variation in N 2 fixation could result from physiological controls at smaller scales, such as soil O 2 availability (Layzell and Hunt 1990). Second, rhizobial strains differ in their effectiveness, and may have differed in vetch nodules across farms, because background soil populations often occupy nodules despite inoculation (Thies et al 1991). Consequently, applying one B value across sites, to account for isotopic fractionation, may not fully meet the assumptions of the natural abundance method.…”

Section: Changes In Labile Organic Matter Pools With a Legumegrass MImentioning

confidence: 99%

Feedbacks between nitrogen fixation and soil organic matter increase ecosystem functions in diversified agroecosystems

Blesh

2019

Ecological Applications

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Nitrogen (N) losses from intensified agriculture are a major cause of global change, due to nitrate (NO 3 À ) export and the eutrophication of aquatic systems as well as emissions of nitrous oxide (N 2 O) into the atmosphere. Diversified agroecosystems with legume cover crops couple N and carbon (C) inputs to soil and reduce N pollution, but there is a need to identify controls on legume N 2 fixation across ecosystems with variable soil conditions. Here, I tested the hypothesis that N mineralization from turnover of soil organic matter (SOM) regulates legume N 2 fixation across 10 farms that spanned a gradient of SOM levels. I separated soil samples into two SOM fractions, based on size and density, which are indicators of soil nutrient cycling and N availability (free particulate organic matter and intra-aggregate particulate organic matter [POM]). This study indicates downregulation of legume N 2 fixation in diversified agroecosystems with increasing N availability in intra-aggregate POM and increasing N mineralization. Intercropping the legume with a grass weakened the relationship between N in POM and N 2 fixation due to N assimilation by the grass. Further, mean rates of N and C mineralization across sites increased with two seasons of a legume-grass cover crop mixture, which could enhance this stabilizing feedback between soil N availability and N 2 fixation over time. These results suggest a potential mechanism for the diversity-ecosystem-function relationships measured in long-term studies of agroecosystems, in which regular use of legume cover crops increases total soil organic C and N and reduces negative environmental impacts of crop production.

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Influence of the Size of Indigenous Rhizobial Populations on Establishment and Symbiotic Performance of Introduced Rhizobia on Field-Grown Legumes

Cited by 350 publications

References 27 publications

Distance‐dependent effects of pathogenic fungi on seedlings of a legume tree: impaired nodule formation and identification of antagonistic rhizosphere bacteria

Distance‐dependent effects of pathogenic fungi on seedlings of a legume tree: impaired nodule formation and identification of antagonistic rhizosphere bacteria

Characterization of soybean Bradyrhizobium strains adapted to the Brazilian savannas

Feedbacks between nitrogen fixation and soil organic matter increase ecosystem functions in diversified agroecosystems

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