Two in the Far North: The Alder‐<i>Frankia</i>Symbiosis, with an Alaskan Case Study

Anderson, Michael D.

doi:10.1002/9780470959404.ch7

Cited by 3 publications

(8 citation statements)

References 121 publications

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“…We assembled a set of reference sequences representing the majority of restriction fragment (RF) types we have encountered in prior published and unpublished studies (Anderson et al 2009, Anderson 2011, and added the new sequences from this study. These strict quality controls steps helped to insure that incorrect base calls would not artificially inflate diversity estimates.…”

Section: Nodule Frankiamentioning

confidence: 99%

“…We have previously hypothesized that this relationship is primarily due to differences in host choice across succession, mostly as a result of early succession alders favoring RF7/OTU3, and late-succession alders reducing selectivity as C partitioning to nodule biomass diminishes over succession (Anderson et al 2009, Anderson 2011. Early-succession alders maintain high leaf N concentrations (Anderson et al 2009), probably to allow high photosynthetic rates made possible by the position of alder in the canopy and demanded by the high growth rates (Viereck et al 1993a) resulting from high intraspecific competition for light in these dense stands.…”

Section: Partner Choicementioning

confidence: 99%

“…Patches of thin-leaf alder within late-successional stands can have densities similar to those seen in mid-succession (Table 1), but these wetter patches, usually defined by relic sloughs, are relatively rare among the dominance by Siberian alder, which is more tolerant of drier soil conditions. Where they co-occur, these conspecific hosts associate with Frankia assemblages that differ in both composition and phylogeny (Anderson et al 2009, Anderson 2011M. D. Anderson, unpublished manuscript).…”

Section: Ecosystem Implicationsmentioning

confidence: 99%

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Ecosystem‐level consequences of symbiont partnerships in an N‐fixing shrub from interior Alaskan floodplains

Ruess

Anderson

McFarland

et al. 2013

Ecological Monographs

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In long-lived N-fixing plants, environmental conditions affecting plant growth and N demand vary at multiple temporal and spatial scales, and symbiont assemblages on a given host and patterns of allocation to nodule activities have been shown to vary according to environmental factors, suggesting that hosts may alter partner choice and manipulate symbiont assemblages based on shifting plant needs. This study assessed economic trade-offs among N-fixing symbionts of thin-leaf alder (Alnus tenuifolia) by examining whether alderFrankia associations change in response to the up-regulation (P fertilization) and downregulation (N-fertilization) of N-fixation activities, and whether these changes are associated with differences among Frankia partners in their relative C cost and/or N benefit to A. tenuifolia.Relative to control plots, alder in þP plots had significantly higher nodule biomass and Nfixation rates; these parameters were significantly lower in þN plots, translating to stand-level N inputs that were more than an order of magnitude greater in þP than þN plots. Nodule respiration and N-fixation rates were positively correlated, and analyses revealed that alder employs mechanisms to increase the efficiency of C use when N fixation is up-regulated. Of the eight Frankia OTUs (operational taxonomic units) identified, two were dominant, with significant differences in Frankia OTU composition across samples being explained by fertilization treatment. Dominant OTUs had similar up-and down-regulatory responses to treatments but differed in C costs of N fixation, while the most abundant sub-dominant failed to up-regulate N-fixation rates in þP plots. Differences among Frankia OTUs in traits relevant to plant performance may form the basis for host choice and explain successional shifts in alder-Frankia assemblages. We suggest that manipulation of Frankia assemblages is an adaptation for a species such as A. tenuifolia that maintains a high dependence on atmospheric N across radically different growth environments. Because of the strong effects of thin-leaf alder on soil N contents, it appears that host changes in C partitioning to nodule activities, including the physiological consequences of host specificity for Frankia assemblages, results in alder both driving and responding to environmental heterogeneity at small to large spatial scales.

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Section: Nodule Frankiamentioning

confidence: 99%

Section: Partner Choicementioning

confidence: 99%

Section: Ecosystem Implicationsmentioning

confidence: 99%

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Ecosystem‐level consequences of symbiont partnerships in an N‐fixing shrub from interior Alaskan floodplains

Ruess

Anderson

McFarland

et al. 2013

Ecological Monographs

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“…Host specificity, genetic variation within suites of compatible bacteria and environmental variation thus represent important potential constraints on the co‐evolution of N‐fixing symbioses (Thompson ; Heath ), on colonization (Parker et al . ), growth and ecosystem functioning (Anderson ) of N‐fixing plants, and on the practical applications of specific N‐fixing systems (e.g. Wheeler & Miller ; Graham & Vance ).…”

Section: Introductionmentioning

confidence: 99%

“…Alders ( Alnus spp., Betulaceae) are trees and shrubs, all species of which are ‘actinorhizal’, that is, form nodules with N‐fixing actinobacteria of the genus Frankia (Dawson ). In Alaska, alders are ecologically important, occurring in the majority of ecoregions across the state, achieving extremely high abundance in some ecosystems, and making significant contributions to the N economy of areas in which they are present (Anderson ). In interior Alaska, symbiotic Frankia assemblages can differ widely between sympatric Alnus spp., and between successional habitats occupied by a given host species (Anderson et al .…”

Section: Introductionmentioning

confidence: 99%

Phylogeny and assemblage composition of Frankia in Alnus tenuifolia nodules across a primary successional sere in interior Alaska

Taylor

Ruess

2013

Molecular Ecology

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In nitrogen (N) fixing symbioses, host-symbiont specificity, genetic variation in bacterial symbionts and environmental variation represent fundamental constraints on the ecology, evolution and practical uses of these interactions, but detailed information is lacking for many naturally occurring N-fixers. This study examined phylogenetic host specificity of Frankia in field-collected nodules of two Alnus species (A. tenuifolia and A. viridis) in interior Alaska and, for A. tenuifolia, distribution, diversity, spatial autocorrelation and correlation with specific soil factors of Frankia genotypes in nodules collected from replicated habitats representing endpoints of a primary sere. Frankia genotypes most commonly associated with each host belonged to different clades within the Alnus-infective Frankia clade, and for A. tenuifolia, were divergent from previously described Frankia. A. tenuifolia nodules from early and late succession habitats harboured distinct Frankia assemblages. In early succession, a single genotype inhabited 71% of nodules with no discernable autocorrelation at any scale, while late succession Frankia were more diverse, differed widely among plants within a site and were significantly autocorrelated within and among plants. Early succession Frankia genotype occurrence was strongly correlated with carbon/nitrogen ratio in the mineral soil fraction, while in late succession, the most common genotypes were correlated with different soil variables. Our results suggest that phylogenetic specificity is a significant factor in the A. tenuifolia-Frankia interaction and that significant habitat-based differentiation may exist among A. tenuifolia-infective genotypes. This is consistent with our hypothesis that A. tenuifolia selects specific Frankia genotypes from early succession soils and that this choice is attenuated in late succession.

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Loss of nitrogen fixing capacity in a montane lichen is linked to increased nitrogen deposition

et al. 2022

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1. The circumboreal/circumpolar N 2 -fixing lichen Stereocaulon vesuvianum is among the most widespread and abundant fruticose species in montane Britain but has lost the capacity to fix N 2 over large areas of the country. 2. To investigate whether loss of N 2 -fixation in S. vesuvianum is linked to increased N deposition, we examined thallus morphology, physiology and chemistry at twelve locations representing an N deposition gradient of 3-40 kg ha −1 year −1 .Measurements were made in parallel on a non-N 2 -fixing reference species (Parmelia saxatilis). The presence or absence of cephalodia (N 2 -fixing nodules containing the cyanobacterium Stigonema sp) was recorded in over 500 herbarium specimens of S. vesuvianum dating back to 1820. 3. Cephalodium abundance in S. vesuvianum, and 15 N concentration in S. vesuvianum and P. saxatilis, were strongly negatively correlated with N deposition and particularly with dry deposited N; cephalodia do not form at total N deposition rates ≥8-9 kg ha −1 year −1 . Other morphological oddities in S. vesuvianum at N-polluted sites include increased apothecium (fungal reproductive structure) production and green algal biofilm development. Biofilm covered thalli without cephalodia lacked nitrogenase activity and cephalodia at sites where they rarely develop had nitrogenase activities typical for this species. The presence or absence of cephalodia in herbarium specimens of S. vesuvianum suggest that the present-day N-deposition linked gradient in N 2 -fixing capacity did not exist in the 19th century and largely developed between 1900-1940. 4. Synthesis. We provide clear evidence that N 2 -fixing capacity in S. vesuvianum has been lost in regions subjected to many decades of enhanced atmospheric N deposition. This loss is consistent with established models of diazotrophy, which identify supply of combined N as an inhibitor of N 2 -fixation. Progressive depletion of thallus 15 N with increasing N deposition is in line with available data indicating that much atmospheric N pollution is 15 N-depleted. Rates of nitrogenase activity in S. vesuvianum are low compared to other symbiotic systems and perhaps more likely supplanted by elevated N deposition. We suggest that | 281

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Two in the Far North: The Alder‐FrankiaSymbiosis, with an Alaskan Case Study

Cited by 3 publications

References 121 publications

Ecosystem‐level consequences of symbiont partnerships in an N‐fixing shrub from interior Alaskan floodplains

Ecosystem‐level consequences of symbiont partnerships in an N‐fixing shrub from interior Alaskan floodplains

Phylogeny and assemblage composition of Frankia in Alnus tenuifolia nodules across a primary successional sere in interior Alaska

Loss of nitrogen fixing capacity in a montane lichen is linked to increased nitrogen deposition

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