mycorrhizae

Melissa K. McCormick, Dennis F. Whigham, Rachel Rock-Blake, Hope E.A. Brooks

North American Orchid Conservation Center (NAOCC) and Smithsonian Environmental Research Center (SERC)

Orchids are widely threatened and endangered worldwide, but efforts to conserve and restore them has been limited by not knowing about the pollinators and fungi they need to grow and reproduce. The absence of appropriate mycorrhizal fungi can limit where orchids grow, but little is known about how the abundance and diversity of appropriate mycorrhizal fungi can affect orchid growth and population dynamics. Light availability is also expected to affect population dynamics, but with orchid life stages occurring predominantly above- or below-ground it seems reasonable to hypothesize that different life stages would be driven by above- or below-ground factors. In particular, emergent, green, above-ground stages would be most impacted by light, while seed, protocorm, and dormant stages would be most affected by mycorrhizal fungi. We hypothesized that the distribution, abundance, and emergence of the globally rare temperate, terrestrial orchid, Isotria medeoloides, would be driven at least partly by their mycorrhizal fungi. We combined the use of specific PCR primers, quantitative real-time PCR, and spatially nested soil samples to measure the distribution and abundance of mycorrhizal fungi that associate with I. medeoloides and measurement of light availability and orchid growth in three distinct studies. We found that I. medeoloides distribution and emergence were affected by the distribution and abundance of their mycorrhizal fungi in the soil. In contrast, plant growth during the growing season and the likelihood of flowering the subsequent year were more affected by light availability. We conclude that orchid conservation and studies of the drivers of orchid population dynamics need to consider both the mycorrhizal fungi and light resources they require.

Contributing Author(s): 
Date Recorded: 
Wednesday, March 4, 2020

Ashley Clayton and Peter Zale, Longwood Gardens

At the Valmont Bog in Hazelton, PA, there are populations of three, state-listed taxa of Platanthera: P. ciliaris, P. blephariglottis, and P. xbicolor, a natural hybrid of the other two species. They are threatened by forest succession, climate change, silt-laden runoff, and herbicide spraying. However, as is the case for most native orchids, conservation efforts are hindered by limited propagation information. To support in situ and ex situ conservation of these species, this experiment was designed to determine the most effective mycorrhizal fungi for in vitro germination of each taxon. In August 2018, pelotons were isolated from the roots of each species and maintained in culture. Multiple capsules from each orchid species were then collected the following month. Seeds were surface sterilized in a 10% bleach solution for 18 minutes and rinsed with distilled water. They were plated on an agar-based medium containing powdered Liriodendron tulipifera wood and inoculated with one of the three fungal isolates. Visual inspection showed that at least 71% of seeds on each plate contained healthy embryos except for seeds originating from one capsule of P. xbicolor, which only about a third had embryos. Visual observation also revealed an association between the hyphae and the rhizoids of protocorms. The peak germination occurred between four and five weeks after sowing. After seven weeks, seed germination ranged from 0 to 27%. Compared to a previous preliminary experiment, the addition of mycorrhizae decreased the time of peak germination from several months to about one month. The effect of each mycorrhiza on germination percentage and protocorm development is still being determined.

Contributing Author(s): 
Date Recorded: 
Friday, May 3, 2019