Physiological diversity of orchids

Abstract

The Orchidaceae is a diverse and wide spread family of flowering plants that are of great value in ornamental, medical, conservation, and evolutionary research. The broad diversity in morphology, growth form, life history, and habitat mean that the members of Orchidaceae exhibit various physiological properties. Epiphytic orchids are often characterized by succulent leaves with thick cell walls, cuticles, and sunken stomata, whereas terrestrial orchids possess rhizomes, corms, or tubers. Most orchids have a long juvenile period, slow growth rate, and low photosynthetic capacity. This reduced photosynthetic potential can be largely explained by CO2 diffusional conductance and leaf internal structure. The amount of light required for plant survival depends upon nutritional mode, growth form, and habitat. Most orchids can adapt to their light environments through morphological and physiological adjustments but are sensitive to sudden changes in irradiance. Orchids that originate from warm regions are susceptible to chilling temperatures, whereas alpine members are vulnerable to high temperatures. For epiphytic orchids, rapid water uptake by the velamen radicum, water storage in their pseudobulbs and leaves, slow water loss, and Crassulacean Acid Metabolism contribute to plant-water balance and tolerance to drought stress. The presence of the velamen radicum and mycorrhizal fungi may compensate for the lack of root hairs, helping with quick absorbance of nutrients from the atmosphere. Under cultivation conditions, the form and concentration of nitrogen affect orchid growth and flowering. However, the limitations of nitrogen and phosphorous on epiphytic orchids in the wild, which require these plants to depend on mycorrhizal fungi for nutrients throughout the entire life cycle, are not clearly understood. Because they lack endosperm, seed germination depends upon obtaining nutrients via mycorrhizal fungi. Adult plants of some autotrophic orchids also gain carbon, nitrogen, phosphorus, and other elements from their mycorrhizal partners. Future studies should examine the mechanisms that determine slow growth and flower induction, the physiological causes of variations in flowering behavior and floral lifespan, the effects of nutrients and atmospheric-nitrogen deposition, and practical applications of mycorrhizal fungi in orchid cultivation.

A comprehensive review on fungal endophytes and its dynamics on Orchidaceae plants: current research, challenges, and future possibilities

“…Orchidaceae are exceptional among all plants as their approach of nutrition involves straight and sometime obligate associations with fungi. Of more than 28,000 known species crossing 763 genera [1,2], over 200 OFEs genera have been investigated for their diversity, which are lower than 30% of the entire orchid genera. Orchidaceae with ornamental, horticultural, medicinal, and commercial applications have been considered for the occurrence of OFEs [20].…”

“…Orchidaceae is one of the largest and most important Chinese Orchidaceae medicinal families (COMFs) of plants, with over 28,000 identified species in about 763 genera species [1,2]. The chief genera from Orchidaceae families are Pleurothallis (over 1000 species), Dendrobium (over 1400 species), Epidendrum (over 1500 species), and Bulbophyllum (over 2000 species).…”

“…This speedy speciation with high COMFs species range is prospectively connected to the family's focused pollination patterns, symbiotic relations with endophytic fungi, epiphytic environments colonization, and metabolism of crassulacean acid. Because of vital evolutionary and ecological consequence of orchids, investigation has long been showed on their biology and associations with diverse fungal endophytes [2].…”

Diversidad y vulnerabilidad de la flora orquideológica de un bosque montano nuboso del Valle Central de Costa Rica

“…Este grupo es susceptible a la reducción y fragmentación del área boscosa porque se aumentan los bordes de bosques y la incidencia de la radiación solar modificando el microclima del sotobosque (Saunders et al 1991). Consecuentemente, en bosques montanos nubosos en México, las orquídeas terrestres solo se encontraron en el interior de fragmentos de bosque y estuvieron ausentes en hábitat alterados (Williams-Linera, Sosa & Platas 1995), lo cual se puede atribuir a su limitada capacidad para tolerar la desecación fuera del bosque (Zhang et al 2018).…”

Similar mycorrhizal fungal communities associated with epiphytic and lithophytic orchids of Coelogyne corymbosa

“…More than 70% of orchids are epiphytic or lithophytic, having evolved from their terrestrial ancestors to adapt to environments that differ in terms of solar radiation, as well as nutrient and water supply ( Gravendeel et al., 2004 ). Orchids with different life forms are characterized by different adaptive structures and functional traits ( Zhang et al., 2018 ), but all have mycorrhizal fungal associations that are very important for their growth, from germination to adulthood ( Yukawa et al., 2009 ; Dearnaley et al., 2012 ). Identifying the community composition of orchid mycorrhizal fungi (OMF) is essential to understanding their biotic mutualisms with orchid species, and the factors influencing OMF composition.…”