How Mycorrhizal Associations Influence Orchid Distribution and Population Dynamics

Abstract

Orchid distribution and population dynamics are influenced by a variety of ecological factors and the formation of holobionts, which play key roles in colonization and ecological community construction. Seed germination, seedling establishment, reproduction, and survival of orchid species are strongly dependent on orchid mycorrhizal fungi (OMF), with mycorrhizal cheating increasingly observed in photosynthetic orchids. Therefore, changes in the composition and abundance of OMF can have profound effects on orchid distribution and fitness. Network analysis is an important tool for the study of interactions between plants, microbes, and the environment, because of the insights that it can provide into the interactions and coexistence patterns among species. Here, we provide a comprehensive overview, systematically describing the current research status of the effects of OMF on orchid distribution and dynamics, phylogenetic signals in orchid–OMF interactions, and OMF networks. We argue that orchid–OMF associations exhibit complementary and specific effects that are highly adapted to their environment. Such specificity of associations may affect the niche breadth of orchid species and act as a stabilizing force in plant–microbe coevolution. We postulate that network analysis is required to elucidate the functions of fungal partners beyond their effects on germination and growth. Such studies may lend insight into the microbial ecology of orchids and provide a scientific basis for the protection of orchids under natural conditions in an efficient and cost-effective manner.

Diversity of Root-Associated Fungi of the Terrestrial Orchids Gavilea lutea and Chloraea collicensis in a Temperate Forest Soil of South-Central Chile

“…This specialization was also detected in OMF independent of the sampling site, showing contrasting communities ( Figure 2 ). Therefore, the dynamic of root-associated fungal communities in the analyzed population seems to depend on the surrounding environment and can have a critical role in the adaptation and fitness of terrestrial orchids in the ecosystem [ 65 , 66 ]. This issue must be considered when designing strategies for safeguarding endangered orchid populations.…”

Effects of a Dark Septate Fungal Endophyte on the Growth and Physiological Response of Seedlings to Drought in an Epiphytic Orchid

“…Because an individual orchid produces thousands of tiny dustlike seeds, they have become fully reliant on typical orchid mycorrhizal fungi (OMF) to induce germination and subsequent establishment of seedlings. Besides, most adult orchids retain mycorrhizal associations as well (Rasmussen and Rasmussen, 2010) and these fungi have been recognized as an important factor influencing the distribution and abundance of orchid populations (McCormick and Jacquemyn, 2014;Pecoraro et al, 2018) and ecological adaptation of orchids (Herrera et al, 2018;Li et al, 2021). However, there is mounting evidence that fungi other than typical OMF reside in the roots of orchids, including DSE (Selosse et al, 2022), but to what extent DSE contribute to the ecology of orchids remains largely unclear.…”

Isolation and identification of beneficial orchid mycorrhizal fungi in Paphiopedilum barbigerum (Orchidaceae)

“… 3 Depending on the presence of functional fungi in cortical cells, orchid fungi are classified as mycorrhizal and nonmycorrhizal fungi. 4 Mycorrhizal fungi (soil saprotrophs), 5 such as Ceratobasidiaceae, Tulasnellaceae , and Sebacinaceae , are collectively referred to as Rhizoctonia ; they increase seed germination as well as the development rate of protocorm and seedlings of orchids. 6–12 However, not all mycorrhizal fungi can promote seed germination, seedling growth, and development of orchids.…”