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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.

To develop next-generation electronic devices, novel semiconductive materials are urgently required. The transition metal dichalcogenides (TMDs) hold the promise of next generation of semiconductor materials for emerging electronic applications. As a member of the group-10 TMDs, PdS2 has a notable layer-number-dependent band structure and tremendously high carrier mobility at room temperature. Here, we demonstrate the experimental realization of centimeter-scale synthesis of the few-layer PdS2 by the combination of physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods. For the first time, the optical anisotropic properties of the few-layer PdS2 were investigated through angle-resolved polarized Raman spectroscopy. Also, the evolution of Raman spectra was studied depending on the temperature in the range of 12–300 K. To further understand the electronic properties of the few-layer PdS2, the field-effect transistor (FET) devices were fabricated and investigated. The electronic measurements of such FET devices reveal that the PdS2 materials exhibit a tunable ambipolar transport mechanism with field-effect mobility of up to ∼388 cm2 V–1 s–1 and the on/off ratio of ∼800, which were not reported before in the literature. To well understand the experimental results, the electronic structure of PdS2 was determined using density functional theory (DFT) calculations. These excellent physical properties are very helpful in developing high-performance opto-electronic applications.

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.

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