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Similarity in mycorrhizal communities associating with two widespread terrestrial orchids decays with distance

Gymnadenia conopsea (L) R Br is an important perennial terrestrial photosynthetic orchid species whose microbiomes are considered to play an important role in helping its germination and growth However, the assemblage of G conopsea root-associated microbial communities is poorly understood The compositions of fungal and bacterial communities from the roots and corresponding soil samples in G conopsea across distinct biogeographical regions from two significantly different altitudes were characterized at the vegetative and reproductive growth stages The geographical location, developmental stage and compartment were factors contributing to microbiome variation in G conopsea Predominant fungal taxa include Ascomycota, Basidiomycota, Mortierellomycota and Chytridiomycota, whereas Proteobacteria, Bacteroidetes, Acidobacteria, Actinobacteria, Verrucomicrobia, Chloroflexi, TM7 and Planctomycetes were predominant bacterial taxa Using G conopsea as a model, the structural and functional composition in G conopsea root-associated microbiomes were comprehensive analyzed Contrary to previous studies, biogeography was the main factor influencing the microbial community in this study Besides, compartment and developmental stage should also be considered to analyze the variation of microbiota composition Although the microbial composition varied greatly by location, the symbiotic microorganisms of G conopsea still have certain specificity This study gives an abundant information of G conopsea root-associated microbiomes and provides new clues to better understanding the factors affecting the composition and diversity of fungal/bacterial communities associated with orchids Our results also laying a foundation for harnessing the microbiome for sustainable G conopsea cultivation Moreover, these results might be generally applicable to other orchidaceae plants

/pdf/the-effect-of-plant-geographical-location-and-developmental-1lvzf47fm2.pdf

The Effect of Plant Geographical Location and Developmental Stage on Root-Associated Microbiomes of Gymnadenia conopsea.

A review for the breeding of orchids: Current achievements and prospects

Orchids form mycorrhizal symbioses with fungi in natural habitats that affect their seed germination, protocorm growth, and adult nutrition. An increasing number of studies indicates how orchids gain mineral nutrients and sometime even organic compounds from interactions with orchid mycorrhizal fungi (OMF). Thus, OMF exhibit a high diversity and play a key role in the life cycle of orchids. In recent years, the high-throughput molecular identification of fungi has broadly extended our understanding of OMF diversity, revealing it to be a dynamic outcome co-regulated by environmental filtering, dispersal restrictions, spatiotemporal scales, biogeographic history, as well as the distribution, selection, and phylogenetic spectrum width of host orchids. Most of the results show congruent emerging patterns. Although it is still difficult to extend them to all orchid species or geographical areas, to a certain extent they follow the "everything is everywhere, but the environment selects" rule. This review provides an extensive understanding of the diversity and ecological dynamics of orchid-fungal association. Moreover, it promotes the conservation of resources and the regeneration of rare or endangered orchids. We provide a comprehensive overview, systematically describing six fields of research on orchid-fungal diversity: the research methods of orchid-fungal interactions, the primer selection in high-throughput sequencing, the fungal diversity and specificity in orchids, the difference and adaptability of OMF in different habitats, the comparison of OMF in orchid roots and soil, and the spatiotemporal variation patterns of OMF. Further, we highlight certain shortcomings of current research methodologies and propose perspectives for future studies. This review emphasizes the need for more information on the four main ecological processes: dispersal, selection, ecological drift, and diversification, as well as their interactions, in the study of orchid-fungal interactions and OMF community structure.

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Progress and Prospects of Mycorrhizal Fungal Diversity in Orchids.

To ensure long-term survival of epiphytic orchids through active reintroduction, more research on critical life cycle stages such as seed germination and seedling establishment are needed. In this study, we used in vitro germination experiments to investigate the role of mycorrhizal fungi in determining seed germination and growth in the endangered epiphytic orchid species, Dendrobium chrysotoxum. Symbiotic seed germination experiments were conducted for 90 days under different light conditions with fungal strains isolated from protocorms of D. chrysotoxum and three sister species. Molecular analyses showed that five strains belonged to the typical orchid mycorrhizal family Tulasnellaceae, whereas the other two strains belonged to the Sebacinaceae and the genus Coprinellus. Fungal inoculation, light conditions, and their interaction had a significant effect on protocorm formation and seedling development. Three fungal isolates, including two from D. chrysotoxum and one from D. catenatum, significantly stimulated protocorm formation and seedling development under light conditions. However, fungi isolated from host protocorms (GC-14 and GC-15) produced the highest number of seedlings after 50 days (49.5 ± 8.5%, 51.3 ± 9.0%, respectively), while the fungus isolated from D. catenatum protocorms produced the maximum number of seedlings only after 90 days (48.7 ± 16.1%). To conclude, this study has shown that light conditions and the identity of fungi had a strong effect on in vitro seed germination and seedling formation in an epiphytic orchid, with fungi isolated from host protocorms leading to accelerated germination and seedling formation. Therefore, fungal source should be taken into account when using seeds and compatible fungi for seedling propagation and in situ reintroduction.

Fungi isolated from host protocorms accelerate symbiotic seed germination in an endangered orchid species (Dendrobium chrysotoxum) from southern China

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The impact of life form on the architecture of orchid mycorrhizal networks in tropical forest

Interactions with mycorrhizal fungi have been increasingly recognized as one of the most important ecological factors determining the distribution and local abundance of orchids. While some orchid species may interact with a variety of fungal associates, others are more specific in their choice of mycorrhizal partners. Moreover, orchids that co-occur at a given site, often associate with different partners, possibly to avoid competition and to allow stable coexistence. However, whether differences in mycorrhizal partners directly affect seed germination and subsequent protocorm formation remains largely unknown. In this research, we used in vitro germination experiments to investigate to what extent seed germination and protocorm formation of Gymnadenia conopsea was affected by the origin and identity of fungal associates. Fungi were isolated from G. conopsea and three other co-occurring orchid species (Dactylorhiza viridis (Coeloglossum viride), Herminium monorchis, and Platanthera chlorantha). In total, eight fungal associates, belonging to Tulasnellaceae, Ceratobasidiaceae, and Serendipitaceae, were successfully isolated and cultured. While all eight fungal strains were able to promote early germination of G. conopsea seeds, only fungal strain GS2, a member of the Ceratobasidiaceae isolated from G. conopsea itself, was able to promote protocorm formation and subsequent growth to a seedling. Two other fungal strains isolated from G. conopsea only supported seed germination until the protocorm formation stage. The other five fungal strains isolated from the co-occurring orchid species did not support seed germination beyond the protocorm stage. We conclude that, although G. conopsea is considered a mycorrhizal generalist that associates with a wide range of fungi during its adult life, it requires specific fungi to promote protocorm formation and growth to a seedling.

Do fungal associates of co-occurring orchids promote seed germination of the widespread orchid species Gymnadenia conopsea?

Orchid-fungus interaction networks often consist of many different fungi that interact with co-occurring orchids in complex ways, but so far it remains largely unclear which processes determine network structure and both ecological and evolutionary mechanisms have been invoked to explain network architecture. In this research, we tested the hypothesis that closely related orchids associate with similar mycorrhizal fungi and vice versa by investigating the architecture of the interaction network between orchid mycorrhizal fungi (OMF) and nine co-occurring epiphytic Dendrobium species. All species grew on the bark of a single tree species (Camelia sinensis) in a traditional tea garden in China, which allowed us to assess the role of evolutionary history in determining the assembly of orchid-fungus communities without the confounding effects of environmental variation. In total, 101 different fungal operational taxonomic units (OTUs) known to be mycorrhizal in orchids were found. Most of the identified mycorrhizal OTUs were members of the Serendipitaceae (80% of all identified mycorrhizal sequences). All orchid species associated with a large number of fungi (average number of links: 31.6 ± 3.8), and orchids from the same species tended to have significantly more similar fungal partners than orchids from different species. The network of interactions was significantly nested (NODF = 41.59, p < 0.01), but not significantly compartmentalized (M = 0.26, Mrandom = 0.27). Phylogenetic analyses showed that the interaction network was not significantly affected by the phylogenies of the orchids or the fungi. Overall, these results indicate that the studied orchid species associated with multiple fungi simultaneously, and that the network of associations was built on asymmetric and weak reciprocal dependences. Associating with multiple fungi may be a successful strategy of orchids to colonize vacant sites and to increase survival of established plants in epiphytic habitats.

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The Architecture of the Network of Orchid–Fungus Interactions in Nine Co-occurring Dendrobium Species

Mycorrhizal fungi play an important role in the germination and growth of orchids essentially influencing their survival, abundance, and spatial distribution. In this study, we investigated the composition of the mycorrhizal fungal community in seven terrestrial orchid species inhabiting Song Mountain, Beijing, China, using Illumina MiSeq high-throughput sequencing. The mycorrhizal communities in the seven orchids were mainly composed of members of the Ceratobasidiaceae, Sebacinales, and Tulasnellaceae, while a number of ectomycorrhizal fungi belonging to the Russulaceae, Tricholomataceae, Thelephoraceae, and Cortinariaceae were occasionally observed. However, the dominant fungal associates and mycorrhizal community differed significantly among the orchid species as well as subhabitats. These findings confirm the previous observation that sympatric orchid species show different preferences for mycorrhizal fungi, which may drive niche partitioning and contribute to their co-occurrence.

Zeyu Zhao

Papers

The impact of life form on the architecture of orchid mycorrhizal networks in tropical forest

Similarity in mycorrhizal communities associating with two widespread terrestrial orchids decays with distance

Do fungal associates of co-occurring orchids promote seed germination of the widespread orchid species Gymnadenia conopsea?

The Architecture of the Network of Orchid–Fungus Interactions in Nine Co-occurring Dendrobium Species

Mycorrhizal fungal community composition in seven orchid species inhabiting Song Mountain, Beijing, China