Loblolly Pine Genetics Structure Its Mycorrhizal Community

Plant populations are constantly exposed to a multitude of biotic and abiotic environmental selection pressures. The ability of a population to persist in or adapt to its environment is heavily influenced by the genetic underpinnings of the traits involved. Thus, in order to understand patterns in current plant populations, and to predict future populations dynamics, an understanding of the genetic basis of adaptive traits is necessary. For example, genetic correlations between traits (driven by pleiotropy or linkage disequilibrium) could influence how species evolve under multiple, conflicting selection pressures, potentially either constraining or enhancing the adaptation of species to each other. The interaction between mycorrhizal fungi and their host trees is a useful system in which to advance the study of how the genetic architecture of traits affects the adaptation of populations. Mycorrhizal fungi are comsymbionts of most plants, deriving mineral nutrients from the soil and transferring them to the host, while the host provides carbohydrates to the fungi. Mycorrhizal fungi have also been shown to affect essential host traits such as drought tolerance, and to alter competitive interactions within and among plant species. In addition to symbiotic interactions belowground with EM fungi, loblolly pine populations are subject to aboveground antagonistic interactions in the form of insect pests and fungal pathogens. Through both laboratory and field experiments, the work presented here explores the degree to which mycorrhizal traits in loblolly pine are genetically determined by the genetics of the host plant, and the degree to which mycorrhizal traits are genetically correlated with other traits. This information will help us to understand how natural and artificial selection focused on one or a few traits of interest (e.g., to mitigate the effects of pests and pathogens) may be indirectly affecting other traits, such as compatibility with symbiotic species belowground, and to better understand how plants may evolve in response to complex suites of selective sources

Interactions of biotic and abiotic environmental factors in an ectomycorrhizal symbiosis, and the potential for selection mosaics

<p>Abstract</p> <p>Background</p> <p>Geographic selection mosaics, in which species exert different evolutionary impacts on each other in different environments, may drive diversification in coevolving species. We studied the potential for geographic selection mosaics in plant-mycorrhizal interactions by testing whether the interaction between bishop pine (<it>Pinus muricata </it>D. Don) and one of its common ectomycorrhizal fungi (<it>Rhizopogon occidentalis </it>Zeller and Dodge) varies in outcome, when different combinations of plant and fungal genotypes are tested under a range of different abiotic and biotic conditions.</p> <p>Results</p> <p>We used a 2 × 2 × 2 × 2 factorial experiment to test the main and interactive effects of plant lineage (two maternal seed families), fungal lineage (two spore collections), soil type (lab mix or field soil), and non-mycorrhizal microbes (with or without) on the performance of plants and fungi. Ecological outcomes, as assessed by plant and fungal performance, varied widely across experimental environments, including interactions between plant or fungal lineages and soil environmental factors.</p> <p>Conclusion</p> <p>These results show the potential for selection mosaics in plant-mycorrhizal interactions, and indicate that these interactions are likely to coevolve in different ways in different environments, even when initially the genotypes of the interacting species are the same across all environments. Hence, selection mosaics may be equally as effective as genetic differences among populations in driving divergent coevolution among populations of interacting species.</p

原著

Mean Plant Response to Mycorrhizal Inoculation (PDF 113 kb

Trait correlations in Loblolly Pine

An examination of trait correlations in Loblolly Pin

The Effect of Local Adaptation on Mycorrhizal Fungi-host Relationships

Background/Question/Methods The successful establishment of a species in a new environment is a result of the complex interaction of genetic, biotic and abiotic factors. Local adaptation, defined as the differential success of genotypes in their native environment relative to a foreign environment, may be one mechanism by which genetic diversity can be maintained within a species; however, it may also lead to divergence of populations and possibly even lead to speciation. Mycorrhizal fungi form symbiotic relationships with 80% of terrestrial plants. These relationships are characterized by the exchange of soil nutrients for carbon from the host. These fungi have been shown to affect essential host traits associated with biotic and to alter competitive interactions within and among plant species. Given the ubiquitous nature of mycorrhizal associations, studies examining plant local adaptation that do not take into account this essential interaction may be missing an important factor in the ability of a plant population to adapt to the environment. Using meta-analysis on a data set comprised of 1591 studies (from 178 papers), we explored the role local adaptation—as determined by relative geographic origin of the plant, fungi, and soil—plays in altering plant response to mycorrhizal fungi. Results/Conclusions Regardless of whether plant, fungus, and/or soil originate in sympatry (same origin) or in allopatry (different origin), the mean effect size of mycorrhizal inoculum on host biomass was positive, emphasizing the mutualistic nature of mycorrhizal fungi relationships. The effect was larger when the plant and fungus originated in sympatry compared to allopatry. Similarly, the effect of mycorrhizal inoculum on host biomass was also larger when the plant and soil originated in sympatry. There was no significant effect of fungal-soil relative origin on effect size. Overall, these results indicate that the effect of mycorrhizal inoculum is positive, but that plant adaptation to local soils and mycorrhizal fungi plays a significant role in altering this effect. While further analyses which account for other sources of variation in experimental outcomes may provide more precise estimates of the importance of local adaptation in mycorrhizal interactions, future experiments considering mycorrhizal fungal relationships should take into account the relative geographic origin of mycorrhiza and the soil used in their experiments

Data from: Genetically determined fungal pathogen tolerance and soil variation influences ectomycorrhizal traits of loblolly pine

1. Selection on genetically correlated traits within species can create indirect effects on one trait by selection on another. The consequences of these trait correlations are of interest because they may influence how suites of traits within species evolve under differing selection pressures, both natural and artificial. 2. By utilizing genetic families of loblolly pine either tolerant (t) or susceptible (s) to two different suites of pathogenic fungi responsible for causing either pine decline (PD) or fusiform rust (FR) disease, we investigated trait variation and trait correlations within loblolly pine (Pinus taeda L.) by determining how ectomycorrhizal (EM) colonization relates to pathogen susceptibility. 3. We detected interactions between susceptibility to pathogenic fungi and soil inoculation source on loblolly pine compatibility with the EM fungi Thelephora, and on relative growth rate of loblolly pine. Additionally, we detected spatial variation in the loblolly pine – EM fungi interaction, and found that variation in colonization rates by some members of the EM community is not dictated by genetic variation in the host plant but rather soil inoculation source alone. 4. The work presented here illustrates the potential for indirect selection on compatibility with symbiotic EM fungi as a result of selection for resistance to fungal pathogens. Additionally, we present evidence that the host plant does not have a single ‘mycorrhizal trait’ governing interactions with all EM fungi, but rather that it can interact with different fungal taxa independently. 5. Synthesis. An understanding of the genetic architecture of essential traits in focal species is crucial if we are to anticipate and manage the results of natural and artificial selection. As demonstrated here, an essential but often overlooked symbiosis (that between plants and mycorrhizal fungi) may be indirectly influenced by directed selection on the host plant

The Effect of Local Adaptation on Mycorrhizal Fungi-host Relationships

Background/Question/Methods The successful establishment of a species in a new environment is a result of the complex interaction of genetic, biotic and abiotic factors. Local adaptation, defined as the differential success of genotypes in their native environment relative to a foreign environment, may be one mechanism by which genetic diversity can be maintained within a species; however, it may also lead to divergence of populations and possibly even lead to speciation. Mycorrhizal fungi form symbiotic relationships with 80% of terrestrial plants. These relationships are characterized by the exchange of soil nutrients for carbon from the host. These fungi have been shown to affect essential host traits associated with biotic and to alter competitive interactions within and among plant species. Given the ubiquitous nature of mycorrhizal associations, studies examining plant local adaptation that do not take into account this essential interaction may be missing an important factor in the ability of a plant population to adapt to the environment. Using meta-analysis on a data set comprised of 1591 studies (from 178 papers), we explored the role local adaptation—as determined by relative geographic origin of the plant, fungi, and soil—plays in altering plant response to mycorrhizal fungi. Results/Conclusions Regardless of whether plant, fungus, and/or soil originate in sympatry (same origin) or in allopatry (different origin), the mean effect size of mycorrhizal inoculum on host biomass was positive, emphasizing the mutualistic nature of mycorrhizal fungi relationships. The effect was larger when the plant and fungus originated in sympatry compared to allopatry. Similarly, the effect of mycorrhizal inoculum on host biomass was also larger when the plant and soil originated in sympatry. There was no significant effect of fungal-soil relative origin on effect size. Overall, these results indicate that the effect of mycorrhizal inoculum is positive, but that plant adaptation to local soils and mycorrhizal fungi plays a significant role in altering this effect. While further analyses which account for other sources of variation in experimental outcomes may provide more precise estimates of the importance of local adaptation in mycorrhizal interactions, future experiments considering mycorrhizal fungal relationships should take into account the relative geographic origin of mycorrhiza and the soil used in their experiments