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Wettewa, Eranga [1], McCormick, Melissa [2], Whigham, Dennis [3].

A qPCR-based approach to disentangling the causes of decline in a population of Corallorhiza odontorhiza (Orchidaceae).

All orchids require associations with mycorrhizal fungi to grow from seeds and they continue that association throughout their lives to varying degrees. Some orchids never become photosynthetic and remain mycoheterotrophic throughout their lives. The relationship between orchid host plants and mycorrhizal fungi may be influenced by both the relative abundance of mycorrhizal fungi and by the presence of specific fungal types that are highly compatible for orchid growth. The fungal community composition and their abundance may directly affect successful recruitment as well as later growth. Simultaneously, abiotic factors such as soil moisture and rainfall can alter fungal community composition and abundance in soil. We aimed to determine whether changes in soil mycorrhizal fungus abundance might have played a role in the dramatic decline of a population of Corallorhiza odontorhiza, a mycoheterotrophic orchid, in recent years. We used a qPCR-based approach to measure the abundance of the Tomentella fungi, the exclusive mycorrhizal associates of C. odontorhiza, in 84 soil samples collected from the site of a population that declined from a high of 842 to only 15 emergent plants. The 50 X 80 m sampling grid is divided into 10 X 10 m subplots. Subplots were classified into three categories based on the presence and density of orchids over the 16-year period that the orchids have been sampled. Soil samples were collected from 11 - 16 plots in each category. Simultaneously, we assessed germination in seed packets at varying distances from emergent plants and quantified Tomentella fungi associated with seed packets with high, low or no seed germination. We hypothesized that the abundance of specific Tomentella fungi in soil samples would be correlated with the abundance of Corallorhiza individuals in subplots. We also hypothesized that fungal abundance would be negatively correlated with distance from emergent plants and positively correlated with germination and protocorm growth in seed packets. We found no relationship between distance from an emergent plant and seed germination or protocorm growth. However, we found that Tomentella spp. were absent in the soil around seed packets that had no germination.  Fungal abundance was consistently lower in the subplots that had not had plants since 1994. Fungal abundance was higher in subplots that historically had numerous plants before the decline. Further studies will be conducted on potential soil fungal pathogens and abiotic stress caused by extended drought conditions that could be the source of population decline.

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1 - Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037, United States
2 - Smithsonian Institution, SERC, 647 Contees Wharf Rd, Edgewater, MD, 21037, United States
3 - Smithsonian Environmental Research Center, 647 Contees Wharf Rd, Edgewater, MD, 21037, United States

Corallorhiza odontorhiza

Presentation Type: Oral Paper
Session: MY3, Mycology: Fungus-Plant Interactions - Ectomycorrhizae and Orchid Mycorrhizae
Location: /
Date: Tuesday, July 20th, 2021
Time: 4:45 PM(EDT)
Number: MY3008
Abstract ID:1031
Candidate for Awards:None

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