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The structure of legume – rhizobium interaction networks and their response to tree invasions

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ABSTRACT

We provide data on how legume-rhizobia interaction webs react to invasions by exotic legumes. This is the first study of its kind and found that general hypotheses derived from above-ground mutualistic webs may not hold for below-ground counterparts. Specifically, we found that legume-rhizobia interactions at the community level are highly specialised resulting in strongly modular webs, which are not nested, and that invasive legumes do not infiltrate existing native webs but rather form unique and novel modules in webs.

No MeSH data available.


Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the betaproteobacteria subclass within the genus Burkholderia. Blue branches indicate collections from legumes at uninvaded sites and red branches subtend those collected from semi and heavily invaded sites. Different symbols and colours at tips correspond to different host plants. Representative taxa from GenBank were included for phylogeny reconstruction. Putative novel species based on DNA distances to previously described species are shown in red above branches. Support for tree topology is given as bootstrap values (>50) at nodes. The inserted ternary diagram illustrates the relative frequency of occurrence of individual bacterial genotypes (black circles) across the three sites where the size of each circle corresponds to the number of bacterial 16S rDNA genotypes. Note that no genotypes were shared between the uninvaded and heavily invaded and one between semi invaded and uninvaded sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.
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plw038-F3: Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the betaproteobacteria subclass within the genus Burkholderia. Blue branches indicate collections from legumes at uninvaded sites and red branches subtend those collected from semi and heavily invaded sites. Different symbols and colours at tips correspond to different host plants. Representative taxa from GenBank were included for phylogeny reconstruction. Putative novel species based on DNA distances to previously described species are shown in red above branches. Support for tree topology is given as bootstrap values (>50) at nodes. The inserted ternary diagram illustrates the relative frequency of occurrence of individual bacterial genotypes (black circles) across the three sites where the size of each circle corresponds to the number of bacterial 16S rDNA genotypes. Note that no genotypes were shared between the uninvaded and heavily invaded and one between semi invaded and uninvaded sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.

Mentions: A total of five native fynbos legumes were identified (A.abietina Thunb., Aspalathus cephalotes Thunb., A.ciliaris L., Aspalathus hispida Thunb., subsp. violacea, and Indigofera cytisoides (L.) L.), all of which were present in the uninvaded site. A.abietina and A. ciliaris were the only native species present in the semi and heavily invaded sites. Invasive Acacia mearnsii, Acacialongifolia and Acaciasaligna were all present at the semi and heavily invaded sites, but the heavily invaded site was dominated by A. mearnsii. Root nodules were present on all native and invasive legumes. Identification using 16S rRNA gene sequences revealed a high diversity of alpha and beta rhizobia associated with both native and alien legumes (Figs. 2 and 3). The majority of alpha rhizobia associated with invasive acacias represented slow-growing Bradyrhizobium spp. (86% of nodule occupants—Table 1, Fig. 2). In contrast, native legumes across all sites were predominantly associated with beta rhizobia (Table 1, Fig. 3), but also formed associations with fast-growing alpha rhizobia, representing strains of Rhizobium and Mesorhizobium, at the uninvaded site. Low sequence similarity (97%, following Kim et al. 2014) between some isolates and accessions from Genbank suggested that novel and currently undescribed species from the genera Bradyrhizobium, Burkholderia, Rhizobium and Mesorhizobium were associated with A.abietina, A. cephalotes subsp. violacea and I.cytisoides (Figs. 2 and 3), one of which was subsequently described as Burkholderia aspalathi (Mavengere et al. 2014).Figure 3.


The structure of legume – rhizobium interaction networks and their response to tree invasions
Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the betaproteobacteria subclass within the genus Burkholderia. Blue branches indicate collections from legumes at uninvaded sites and red branches subtend those collected from semi and heavily invaded sites. Different symbols and colours at tips correspond to different host plants. Representative taxa from GenBank were included for phylogeny reconstruction. Putative novel species based on DNA distances to previously described species are shown in red above branches. Support for tree topology is given as bootstrap values (>50) at nodes. The inserted ternary diagram illustrates the relative frequency of occurrence of individual bacterial genotypes (black circles) across the three sites where the size of each circle corresponds to the number of bacterial 16S rDNA genotypes. Note that no genotypes were shared between the uninvaded and heavily invaded and one between semi invaded and uninvaded sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4940501&req=5

plw038-F3: Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the betaproteobacteria subclass within the genus Burkholderia. Blue branches indicate collections from legumes at uninvaded sites and red branches subtend those collected from semi and heavily invaded sites. Different symbols and colours at tips correspond to different host plants. Representative taxa from GenBank were included for phylogeny reconstruction. Putative novel species based on DNA distances to previously described species are shown in red above branches. Support for tree topology is given as bootstrap values (>50) at nodes. The inserted ternary diagram illustrates the relative frequency of occurrence of individual bacterial genotypes (black circles) across the three sites where the size of each circle corresponds to the number of bacterial 16S rDNA genotypes. Note that no genotypes were shared between the uninvaded and heavily invaded and one between semi invaded and uninvaded sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.
Mentions: A total of five native fynbos legumes were identified (A.abietina Thunb., Aspalathus cephalotes Thunb., A.ciliaris L., Aspalathus hispida Thunb., subsp. violacea, and Indigofera cytisoides (L.) L.), all of which were present in the uninvaded site. A.abietina and A. ciliaris were the only native species present in the semi and heavily invaded sites. Invasive Acacia mearnsii, Acacialongifolia and Acaciasaligna were all present at the semi and heavily invaded sites, but the heavily invaded site was dominated by A. mearnsii. Root nodules were present on all native and invasive legumes. Identification using 16S rRNA gene sequences revealed a high diversity of alpha and beta rhizobia associated with both native and alien legumes (Figs. 2 and 3). The majority of alpha rhizobia associated with invasive acacias represented slow-growing Bradyrhizobium spp. (86% of nodule occupants—Table 1, Fig. 2). In contrast, native legumes across all sites were predominantly associated with beta rhizobia (Table 1, Fig. 3), but also formed associations with fast-growing alpha rhizobia, representing strains of Rhizobium and Mesorhizobium, at the uninvaded site. Low sequence similarity (97%, following Kim et al. 2014) between some isolates and accessions from Genbank suggested that novel and currently undescribed species from the genera Bradyrhizobium, Burkholderia, Rhizobium and Mesorhizobium were associated with A.abietina, A. cephalotes subsp. violacea and I.cytisoides (Figs. 2 and 3), one of which was subsequently described as Burkholderia aspalathi (Mavengere et al. 2014).Figure 3.

View Article: PubMed Central - PubMed

ABSTRACT

We provide data on how legume-rhizobia interaction webs react to invasions by exotic legumes. This is the first study of its kind and found that general hypotheses derived from above-ground mutualistic webs may not hold for below-ground counterparts. Specifically, we found that legume-rhizobia interactions at the community level are highly specialised resulting in strongly modular webs, which are not nested, and that invasive legumes do not infiltrate existing native webs but rather form unique and novel modules in webs.

No MeSH data available.