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

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.


Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the alphaproteobacteria subclass. 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 with taxon names indicated in black. * indicate Bradyrhizobium spp. previously isolated from Australian legumes, ** those isolated from acacias and *** those isolated from CFR legumes. 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 invaded (semi and heavily invaded) 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-F2: Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the alphaproteobacteria subclass. 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 with taxon names indicated in black. * indicate Bradyrhizobium spp. previously isolated from Australian legumes, ** those isolated from acacias and *** those isolated from CFR legumes. 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 invaded (semi and heavily invaded) sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.

Mentions: Next we explored the frequency of nodule occupancy by major bacterial clades (i.e. alpha rhizobia—slow-growing Bradyrhizobium clade (Fig. 1, clade A), alpha rhizobia—fast-growing ‘Rhizobium’ clade (Fig. 1, clade B), beta rhizobia—Burkholderia spp. (Fig. 2)) across sites and between native and invasive legumes. Data from the partially and heavily invaded sites were combined for these analyses as our networks revealed very similar bacterial communities and interactions. We used G-tests to ask (i) whether differences in the frequency of nodule occupancy by bacteria in these major clades differs between invasive and native legumes at the invaded sites and (ii) whether composition of nodule occupants changes across the invasion gradient in the native species present at uninvaded and invaded sites (i.e. for Aspalathus abietina and Aspalathusciliaris).Figure 2.


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 alphaproteobacteria subclass. 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 with taxon names indicated in black. * indicate Bradyrhizobium spp. previously isolated from Australian legumes, ** those isolated from acacias and *** those isolated from CFR legumes. 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 invaded (semi and heavily invaded) 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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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4940501&req=5

plw038-F2: Phylogeny based on partial 16S rDNA sequences for rhizobia taxa belonging to the alphaproteobacteria subclass. 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 with taxon names indicated in black. * indicate Bradyrhizobium spp. previously isolated from Australian legumes, ** those isolated from acacias and *** those isolated from CFR legumes. 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 invaded (semi and heavily invaded) sites, whereas most genotypes present at the semi-invaded site were also present in similar frequencies at the heavily invaded site.
Mentions: Next we explored the frequency of nodule occupancy by major bacterial clades (i.e. alpha rhizobia—slow-growing Bradyrhizobium clade (Fig. 1, clade A), alpha rhizobia—fast-growing ‘Rhizobium’ clade (Fig. 1, clade B), beta rhizobia—Burkholderia spp. (Fig. 2)) across sites and between native and invasive legumes. Data from the partially and heavily invaded sites were combined for these analyses as our networks revealed very similar bacterial communities and interactions. We used G-tests to ask (i) whether differences in the frequency of nodule occupancy by bacteria in these major clades differs between invasive and native legumes at the invaded sites and (ii) whether composition of nodule occupants changes across the invasion gradient in the native species present at uninvaded and invaded sites (i.e. for Aspalathus abietina and Aspalathusciliaris).Figure 2.

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.