[Show abstract][Hide abstract] ABSTRACT: Arbuscular mycorrhizal fungi (AMF) are highly successful plant symbionts. They reproduce clonally producing multinucleate spores. It has been suggested that some AMF harbor genetically different nuclei. However, recent advances in sequencing the Glomus irregulare genome have indicated very low within-fungus polymorphism. We tested the null hypothesis that, with no genetic differences among nuclei, no significant genetic or phenotypic variation would occur among clonal single spore lines generated from one initial AMF spore. Furthermore, no additional variation would be expected in the following generations of single spore lines. Genetic diversity contained in one initial spore repeatedly gave rise to genetically different variants of the fungus with novel phenotypes. The genetic changes represented quantitative changes in allele frequencies, most probably as a result of changes in the frequency of genetic variation partitioned on different nuclei. The genetic and phenotypic variation is remarkable, given that it arose repeatedly from one clonal individual. Our results highlight the dynamic nature of AMF genetics. Even though within-fungus genetic variation is low, some is probably partitioned among nuclei and potentially causes changes in the phenotype. Our results are important for understanding AMF genetics, as well as for researchers and biotechnologists hoping to use AMF genetic diversity for the improvement of AMF inoculum.
New Phytologist 08/2012; 196(3):853-61. · 6.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background and aims
Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth.
In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems.
The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, ‘nurse’ plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth.
Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.
Plant and Soil 06/2012; 363(1-2):345-356. · 3.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The diversity of plants and arbuscular mycorrhizal fungi (AMF) has been experimentally shown to alter plant and AMF productivity. However, little is known about how plant and AMF diversity interact to shape their respective productivity.
We co-manipulated the diversity of both AMF and plant communities in two greenhouse studies to determine whether the productivity of each trophic group is mainly influenced by plant or AMF diversity, respectively, and whether there is any interaction between plant and fungal diversity. In both experiments we compared the productivity of three different plant species monocultures, or their respective 3-species mixtures. Similarly, in both studies these plant treatments were crossed with an AMF diversity gradient that ranged from zero (non-mycorrhizal controls) to a maximum of three and five taxonomically distinct AMF taxa, respectively. We found that within both trophic groups productivity was significantly influenced by taxon identity, and increased with taxon richness. These main effects of AMF and plant diversity on their respective productivities did not depend on each other, even though we detected significant individual taxon effects across trophic groups.
Our results indicate that similar ecological processes regulate diversity-productivity relationships within trophic groups. However, productivity-diversity relationships are not necessarily correlated across interacting trophic levels, leading to asymmetries and possible biotic feedbacks. Thus, biotic interactions within and across trophic groups should be considered in predictive models of community assembly.
PLoS ONE 01/2012; 7(5):e36950. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Terminal restriction fragment length polymorphism (T-RFLP) analysis is a common technique used to characterize soil microbial diversity. The fidelity of this technique in accurately reporting diversity has not been thoroughly evaluated. Here we determine if rare fungal species can be reliably detected by T-RFLP analysis. Spores from three arbuscular mycorrhizal fungal species were each mixed at a range of concentrations (1%, 10%, 50%, and 100%) with Glomus irregulare to establish a minimum detection threshold. T-RFLP analysis was capable of detecting diagnostic peaks of rare taxa at concentrations as low as 1%. The relative proportion of the target taxa in the sample and DNA concentration influenced peak detection reliability. However, low concentrations produced small, inconsistent electropherogram peaks contributing to difficulty in differentiating true peaks from signal noise. The results of this experiment suggest T-RFLP is a reproducible and high fidelity procedure, which requires careful data interpretation in order to accurately characterize sample diversity.
Journal of microbiological methods 01/2012; 88(1):14-8. · 2.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the process of plant domestication, below-ground communities are rarely considered. Some studies have attempted to understand the changes in root symbionts owing to domestication, but little is known about how it influences mycorrhizal response in domesticated crops. We hypothesized that selection for above-ground traits may also result in decreased mycorrhizal abundance in roots. Breadfruit (Artocarpus sp.) has a long domestication history, with a strong geographical movement of cultivars from west to east across the Melanesian and Polynesian islands. Our results clearly show a decrease in arbuscular mycorrhizas (AMs) along a domestication gradient from wild to recently derived cultivars. We showed that the vesicular and arbuscular colonization rate decreased significantly in more recently derived breadfruit cultivars. In addition, molecular analyses of breadfruit roots indicated that AM fungal species richness also responded along the domestication gradient. These results suggest that human-driven selection for plant cultivars can have unintended effects on below-ground mutualists, with potential impacts on the stress tolerance of crops and long-term food security.
Proceedings of the Royal Society B: Biological Sciences 09/2011; 279(1731):1122-30. · 5.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous research has found that conventional agricultural systems adversely affect arbuscular mycorrhizal (AM) fungi. However, there is little information on how more ecologically sustainable agricultural practices such as tree-based intercropping (TBI) influence AM fungal communities. In this study, we investigated whether TBI promotes a more abundant and diverse AM fungal community compared to conventional monocropping (CM). Abundance was estimated by measuring spore abundance and hyphal length in soil, and AM fungal colonization of corn (Zea mays) roots. Overall, AM fungal abundance was similar in both systems as corn roots from the CM and TBI systems were heavily colonized (> 50%) by AM fungi throughout the growing season. Additionally, soil samples from the CM and TBI systems contained similar spore densities and hyphal length. Molecular analysis of the AM fungal community was assessed using terminal restriction fragment length polymorphism (T-RFLP) analysis of large subunit rRNA genes amplified from roots in the two cropping systems. A total of fourteen AM fungal phylotypes that belonged to the Glomeraceae were found in the two cropping systems. The TBI system had a higher AM fungal richness and contained several taxa not found in the CM system. Molecular analysis of AM fungal communities also revealed significant temporal and compositional differences between the TBI and CM systems. Within the TBI system, tree species differentially influenced the AM fungal community composition in the alley cropping regions. Future research should focus on determining whether compositional differences among AM fungal communities in CM and TBI systems have a functional effect on crop growth and productivity.
Soil Biology and Biochemistry 08/2011; 45:172-180. · 4.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Introduced, non-native organisms are of global concern, because biological invasions can negatively affect local communities.
Arbuscular mycorrhizal (AM) fungal communities have not been well studied in this context. AM fungi are abundant in most soils,
forming symbiotic root-associations with many plant species. Commercial AM fungal inocula are increasingly spread worldwide,
because of potentially beneficial effects on plant growth. In contrast, some invasive plant species, such as the non-mycorrhizal
Alliaria petiolata, can negatively influence AM fungi. In a greenhouse study we examined changes in the structure of a local Canadian AM fungal
community in response to inoculation by foreign AM fungi and the manipulated presence/absence of A. petiolata. We expected A. petiolata to have a stronger effect on the local AM fungal community than the addition of foreign AM fungal isolates. Molecular analyses
indicated that inoculated foreign AM fungi successfully established and decreased molecular diversity of the local AM fungal
community in host roots. A. petiolata did not affect molecular diversity, but reduced AM fungal growth in the greenhouse study and in a in vitro assay. Our findings
suggest that both introduced plants and exotic AM fungi can have negative impacts on local AM fungi.
KeywordsArbuscular mycorrhizal fungi (AMF)–
–Inoculation–Fungal invasion–Community ecology–
[Show abstract][Hide abstract] ABSTRACT: Tree-based intercropping (TBI) is an ecologically sustainable agricultural practice that may promote a more diverse arbuscular mycorrhizal (AM) fungal community compared to conventional systems, but the influence of the dynamics of these systems on AM fungi has not been established. Soil and root samples were collected in the intercropping alleys along transects perpendicular to tree rows occupied by white ash (Fraxinus americana), poplar (Populus deltoids×nigra), Norway spruce (Picea abies), and rows without trees (control). Molecular analysis of the AM fungal community at the TBI site revealed 17 phylotypes belonging to the Glomeraceae. Overall, the AM fungal community in the TBI site was comparable to other conventional agricultural systems; with the majority of phylotypes belonging to Glomus group A. AM fungal phylotype richness and community composition significantly differed among the treatments in the TBI site. AM fungal communities were more diverse in cropping alleys adjacent to trees that associate with AM fungi than trees that do not associate with AM fungi. Norway spruce had a negative influence on the AM fungal community as tree rows and bordering intercropping alleys had a significantly lower phylotype richness and different community composition. These results suggest that to maintain a diverse AM fungal community throughout TBI systems, it may be best to incorporate tree species that associate with AM fungi.
[Show abstract][Hide abstract] ABSTRACT: A considerable amount of phenotypic, genetic and symbiotic functional variability has been documented in arbuscular mycorrhizal fungi (AMF). However, little is known about whether distinct AMF ecotypes have evolved within their geographic range. We tested the hypothesis that AMF growing at temperatures closer to those prevalent within their origin would benefit their host and grow more than isolates distant from their native conditions. For each of six AMF species, we chose pairs of isolates that originated from distant areas with contrasting climates. Each isolate was grown in association with two grass species of different thermal optima at two temperature settings. Thus, we also tested whether AMF from different climatic origins were dependent on the thermal adaptation of the host plant species or to temperature per se. Although fungal growth was not directly affected by temperature, we found that AMF isolates originating from contrasting climates consistently and differentially altered plant growth. Our results suggest that AMF from contrasting climates have altered symbiotic function, thus linking an abiotic factor to ecotypic differentiation of putatively important symbionts.
New Phytologist 09/2010; 189(2):507-14. · 6.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: * Arbuscular mycorrhizal fungi (AMF) are plant symbionts that improve floristic diversity and ecosystem productivity. Many AMF species are generalists with wide host ranges. Arbuscular mycorrhizal fungi individuals are heterokaryotic, and AMF populations are genetically diverse. Populations of AMF harbor two levels of genetic diversity on which selection can act, namely among individuals and within individuals. Whether environmental factors alter genetic diversity within populations is still unknown. * Here, we measured genetic changes and changes in fitness-related traits of genetically distinct AMF individuals from one field, grown with different concentrations of available phosphate or different host species. * We found significant genotype-by-environment interactions for AMF fitness traits in response to these treatments. Host identity had a strong effect on the fitness of different AMF, unearthing a specificity of response within Glomus intraradices. Arbuscular mycorrhizal fungi individuals grown in novel environments consistently showed a reduced presence of polymorphic genetic markers, providing some evidence for host or phosphate-induced genetic change in AMF. * Given that AMF individuals can form extensive hyphal networks colonizing different hosts simultaneously, contrasting habitats or soil properties may lead to evolution in the population. Local selection may alter the structure of AMF populations and maintain genetic diversity, potentially even within the hyphal network of one fungus.
New Phytologist 09/2009; 184(2):412-23. · 6.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Glyphosate-resistant (GR) cropping systems change the soil environment by introducing novel compounds and glyphosate into the soil environment. Over one growing season, we examined the effect of both the transgenic corn and the use of glyphosate on two groups of rhizosphere microbes, denitrifying bacteria and fungi. Using quantitative PCR to measure microbe abundance, and terminal restriction fragment length polymorphism (T-RFLP) to measure community structure, we found neither crop type (transgenic or conventional) nor herbicide (glyphosate or conventional) affected rhizosphere denitrifying or fungal communities. Instead, our results showed that seasonality was a significant determinant of denitrifier and fungal abundance as well as their diversity in this study, suggesting in the short term, some microbial communities are robust to changes in their environment by GR crops.
[Show abstract][Hide abstract] ABSTRACT: Arbuscular mycorrhizal fungi (AMF) form symbioses with the majority of plants and form extensive underground hyphal networks simultaneously connecting the roots of different plant species. No empirical evidence exists for either anastomosis between genetically different AMF or genetic exchange.Five isolates of one population of Glomus intraradices were used to study anastomosis between hyphae of germinating spores. We show that genetically distinct AMF, from the same field, anastomose, resulting in viable cytoplasmic connections through which genetic exchange could potentially occur.Pairs of genetically different isolates were then co-cultured in an in vitro system.Freshly produced spores were individually germinated to establish new cultures.Using several molecular tools, we show that genetic exchange occurred between genetically different AMF. Specific genetic markers from each parent were transmitted to the progeny. The progeny were viable, forming symbioses with plant roots. The phenotypes of some of the progeny were significantly different from either parent.Our results indicate that considerable promiscuity could occur in these fungi because nine out of 10 combinations of different isolates anastomosed. The ability to perform genetic crosses between AMF experimentally lays a foundation for understanding the genetics and evolutionary biology of these important plants symbionts.
New Phytologist 01/2009; 181(4):924-37. · 6.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of commercial arbuscular mycorrhizal (AM) inoculants is growing. However, we know little about how resident AM communities
respond to inoculations under different soil management conditions. The objective of this study was to simulate the application
of a commercial AM fungal inoculant of Glomus intraradices to soil to determine whether the structure and functioning of that soil’s resident AM community would be affected. The effects
of inoculation were investigated over time under disturbed or undisturbed soil conditions. We predicted that the introduction
of an infective AM fungus, such as G. intraradices, would have greater consequences in disturbed soil. Using a combination of molecular (terminal restriction length polymorphism
analysis based on the large subunit of the rRNA gene) and classical methods (AM fungal root colonization and P nutrition)
we found that, contrary to our prediction, adding inoculant to soil containing a resident AM fungal community does not necessarily
have an impact on the structure of that community either under disturbed or undisturbed conditions. However, we found evidence
of positive effects of inoculation on plant nutrition under disturbed conditions, suggesting that the inoculant interacted,
directly or indirectly, with the resident AM fungi. The inoculant significantly improved the P content of the host but only
in presence of the resident AM fungal community. In contrast to inoculation, soil disturbance had a significant negative impact
on species richness of AM fungi and influenced the AM fungal community composition as well as its functioning. Thus, we conclude
that soil disturbance may under certain conditions have greater consequences for the structure of resident AM fungal communities
in agricultural soils than commercial AM fungal inoculations with G. intraradices.
Plant and Soil 01/2009; 317(1):257-266. · 3.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Different species of arbuscular mycorrhizal fungi (AMF) alter plant growth and affect plant coexistence and diversity. Effects of within-AMF species or within-population variation on plant growth have received less attention. High genetic variation exists within AMF populations. However, it is unknown whether genetic variation contributes to differences in plant growth. In our study, a population of AMF was cultivated under identical conditions for several generations prior to the experiments thus avoiding environmental maternal effects. We show that genetically different Glomus intraradices isolates from one AMF population significantly alter plant growth in an axenic system and in greenhouse experiments. Isolates increased or reduced plant growth meaning that plants potentially receive benefits or are subject to costs by forming associations with different individuals in the AMF population. This shows that genetic variability in AMF populations could affect host-plant fitness and should be considered in future research to understand these important soil organisms.
[Show abstract][Hide abstract] ABSTRACT: Arbuscular mycorrhizal fungi (AMF) are ecologically important root symbionts of most terrestrial plants. Ecological studies of AMF have concentrated on differences between species; largely assuming little variability within AMF species. Although AMF are clonal, they have evolved to contain a surprisingly high within-species genetic variability, and genetically different nuclei can coexist within individual spores. These traits could potentially lead to within-population genetic variation, causing differences in physiology and symbiotic function in AMF populations, a consequence that has been largely neglected. We found highly significant genetic and phenotypic variation among isolates of a population of Glomus intraradices but relatively low total observed genetic diversity. Because we maintained the isolated population in a constant environment, phenotypic variation can be considered as variation in quantitative genetic traits. In view of the large genetic differences among isolates by randomly sampling two individual spores, <50% of the total observed population genetic diversity is represented. Adding an isolate from a distant population did not increase total observed genetic diversity. Genetic variation exceeded variation in quantitative genetic traits, indicating that selection acted on the population to retain similar traits, which might be because of the multigenomic nature of AMF, where considerable genetic redundancy could buffer the effects of changes in the genetic content of phenotypic traits. These results have direct implications for ecological research and for studying AMF genes, improving commercial AMF inoculum, and understanding evolutionary mechanisms in multigenomic organisms.
Proceedings of the National Academy of Sciences 03/2004; 101(8):2369-74. · 9.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Summary • Cuscuta spp. are holoparasitic plants that can simultaneously parasitise several host plants. It has been suggested that Cuscuta has evolved a foraging strategy based on a positive relationship between preuptake investment and subsequent reward on different host species. • Here, we establish reliable parasite size measures and show that parasitism on individuals of different host species alters the biomass of C. campestris , but that, within host species size and age, also contributes to the heterogeneous resource landscape. •W e then performed two additional experiments to test whether C. campestris achieves greater resource acquisition by parasitising two host species rather than one and, whether C. campestris forages in communities of hosts offering different rewards (a choice experiment). • There was no evidence in either experiment for direct benefits of a mixed host diet. Cuscuta campestris foraged by parasitising the most rewarding hosts the fastest and then investing the most on them. We conclude that our data present strong evi- dence for foraging in the parasitic plant C. campestris .
New Phytologist 01/2004; 162(1):147 - 155. · 6.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The importance of a spatial context in understanding the ecology and evolution of organisms has become increasingly clear.
Although there is a growing awareness of the importance of mycorrhizal fungi in many communities and ecosystems, much of this
understanding is based on a spatially homogenized view of these soil fungi. This homogenized approach may limit our understanding
of how these organisms interact with plants and other biota in the field. As an attempt to advance a spatial framework for
understanding mycorrhizal ecology, we review our current understanding of the spatial structure of communities and populations
of ectomycorrhizal and arbuscular mycorrhizal fungi at the scale of landscapes, communities, and individual host root systems.
A variety of potential mechanisms such as disturbance, abiotic and biotic dispersal of mycorrhizal propagules, and biotic
interactions may be responsible for generating and maintaining this spatial variation of populations and communities, but
the links between observed spatial patterns and mechanisms have yet to be formed. Future work assessing the potential functional
significance of spatial variation of mycorrhizal fungi for plant communities and ecosystem function, as well as measuring
spatial variation in mycorrhizal function, will continue to advance our understanding of the spatial template for mycorrhizal–plant
interactions in the field.