Stability of Markers Used for Identification of Two Rhizobium galegae Inoculant Strains after Five Years in the Field

Diversity and Distributions

2001

129

113

Because hereditary symbiont transmission is normally absent in the mutualism of legume plants and root‐nodule bacteria (rhizobia), dispersing plants may often arrive at new habitats where mutualist partners are too rare to provide full benefits. Factors governing invasion success were explored by analysing a system of two coupled pairwise competition models: a legume invader competing with a resident non‐mutualistic plant, and a rhizobial population competing with a resident population of nonsymbiotic bacteria. The non‐linear dependence of benefits on partner abundance in this mutualism creates the possibility of two alternative population size equilibria, so that a threshold density can exist for invasion. If legumes and rhizobia exceed a critical population size, both species achieve rapid population growth, while if initial densities of both species are below their respective thresholds, they remain rare and are thus vulnerable to extinction in the presence of competitors. Overall, the results indicate that legumes may often fail at colonization attempts within habitats where mutualist partners are scarce. Data on legume prevalence in island floras and rates of geographical spread by legume weeds are consistent with this inference. Predictive insights about invasiveness may emerge from comparative research on key traits identified by the model, especially the shape of the function determining the number of nodules formed at low rhizobial density.

Section: Discussionmentioning

confidence: 99%

Mutualism as a constraint on invasion success for legumes and rhizobia

Diversity and Distributions

2001

129

113

“…Numerous cases have been reported in which legumes fail to form nodules when first introduced to a new geographical region (Wilson, 1934;Hely, 1957;Bottomley & Jenkins, 1983;Halliday & Somasegaran, 1983;Kueneman et al ., 1984;Woomer et al ., 1988;Lindstrom et al ., 1990;Odee et al ., 1995;Sullivan et al ., 1995). Thus, it is clear that legume colonists can sometimes experience a scarcity of compatible rhizobia when they first arrive in a new habitat.…”

Section: Introductionmentioning

confidence: 99%

Growth of an invasive legume is symbiont limited in newly occupied habitats

Małek²,

Diversity and Distributions

2006

118

Mutualisms may play an important role in the establishment and invasion success of introduced species, but their influence is little studied. To test whether a lack of root nodule symbionts may limit the performance of invasive legumes, seedlings of Cytisus scoparius were introduced to an old-field habitat and then either inoculated with Bradyrhizobium strains from existing C. scoparius populations, or left uninoculated. In two separate years, inoculation more than doubled average plant biomass. For uninoculated transplants, nodule formation was positively correlated with proximity to plants of the native legume Desmodium canadense , but not related to distance from a second legume species, Apios americana. Polymerase chain reaction assays and DNA sequencing confirmed that bacteria isolated from uninoculated C. scoparius plants were indistinguishable from Bradyrhizobium strains in root nodules of D. canadense . By contrast, bacterial strains associated with A. americana were never found in C. scoparius nodules. Transplants in seven other habitats across a 160 km region also showed a highly significant, fivefold biomass increase in response to inoculation. Thus, colonizing legumes can suffer from a scarcity of nodule symbionts. However, certain indigenous legumes may create favourable microhabitats for invasion, by increasing symbiont availability in their vicinity.

FEMS Microbiology Letters

“…In a field study a goat's rue field was inoculated with a mixture of R. galegae 1461 with long O‐chain LPS and HAMBI 540 (the parental strain of 1174) with short O‐chain LPS. When the strains were recovered 5 years after inoculation, both the long O‐chain and the short O‐chain LPS phenotypes persisted equally well in soil [25]. Because the tolerance of acidic medium was associated with long‐chain LPS type and production of EPS, long O‐chain LPS and abundant EPS production can thus serve as selection criteria when developing inoculants for acidic soils.…”

Section: Resultsmentioning

confidence: 99%

Stability of short and long O-chain lipopolysaccharide types in Rhizobium galegae and their correlation with symbiotic properties and growth conditions, tolerance of low pH, aluminum and salt in the growth medium

Rásänen

Lindström

2006

We recently showed that Rhizobium galegae strains had two different lipopolysaccharide types, short and long O‐chain. In the present study we observed that the lipopolysaccharide type was a stable feature of the strain. Both types persisted in cells at all phases of the growth cycle, during differentiation of bacteria into bacteroids and when the cells were grown under environmental stress. When R. galegae strains were grown at low pH or in medium containing aluminum or salt, simulating conditions in acid soils of temperate regions and osmotic stress, respectively, the tolerance of low pH was associated with the long O‐chain lipopolysaccharide and abundant acidic polysaccharide production.