Does the spatial distribution of free-living orchid mycorrhizal fungi determine the local distribution of tropical epiphytic orchids?

Understanding the factors that limit species distributions is a longstanding question in ecology. In land plants, species distributions are simultaneously limited by multiple factors, including climate, dispersal ability, and species' physiological tolerance. The ecological requirements of obligate inter-specific interactions impose additional, often overlooked, limitations. How complex interactions influence plant species distribution has received little attention despite its relevance for species conservation in the face of global change. This project will address this gap by investigating how two obligate partners, interacting with abiotic factors, influence plant distribution in seasonally-dry tropical forests. Tropical epiphytic orchids provide an exceptional study model because they depend on two partners to germinate and grow: a host tree and mycorrhizal fungi. In particular, free-living mycorrhizal communities are an understudied aspect of orchid's needs that may influence seedling establishment success. We propose to study which factors, whether mycorrhiza availability on trees, micro-environmental gradients, or spatial effects, determine the distribution of tropical epiphytic orchids. We will examine how host trees and mycorrhizal fungal diversity affect the local distribution of orchid species. In particular, we will investigate whether trees colonized and non-colonized by orchids harbour contrasting communities of mycorrhizal fungi; whether abiotic factors such as temperature, humidity and light availability affect the distribution of orchids in a direct manner or indirectly through affecting the distribution of free-living mycorrhizal fungi; and whether spatial effects, such as dispersal limitations, might constrain the local distribution range of both orchids and their mycorrhizal partners. The methodology combines collection of field data in a seasonally-dry tropical forest, cutting-edge techniques in molecular biology (mycorrhizal DNA meta-barcoding), and advanced statistical analyses (quantitative community ecology and spatial point-pattern analysis). This study will provide a better understanding of the ecological factors influencing the constraints to the local distribution of tropical epiphytic orchids. Obtaining such information is a pressing issue for informing conservation actions in the endemism-rich dry forests of the Cauca Valley. The outcomes of this project will positively impact in-situ conservation of orchids, ecological theory, and the operative capacity of the research groups of PUJ-Cali and collaborators. Specifically, the results will be applicable to designing targeted conservation actions for local endemic species, such as Cattleya quadricolor, and will unveil for the first time a largely neglected component of tropical forest diversity that are bark-dwelling fungi. This project represents a pioneer effort towards understanding the availability of free-living mycorrhizal communities on the bark of phorophytes and non-phorophyte trees. This will be one of the first studies of the kind in the scientific literature and will push the state of the art forward by determining not only the drivers of orchid presence, but importantly of orchid absence from trees. Finally, the acquisition of a MinION sequencer will represent an important technological up-grade for the PUJ laboratory. This portable device for high-throughput DNA sequencing will greatly improve the efficiency of the molecular procedures used by the researchers involved, contribute to lower lab occupancy, and eliminate the costs, delays, and legal paperwork associated with sample exportation for sequencing by foreign sequencing services.