Fungal Diversity in Sarracenia Purpurea Pitchers at Harvard Forest 2009-2010

The carnivorous pitcher plant Sarracenia purpurea is widely distributed in the United States and Canada, and is host to a variety of symbiotic organisms, including symbiotic fungi. Culturing of S. purpurea pitcher contents in its native range uncovers diverse single-celled (yeast) communities; these yeast communities are dominated by the ascomycete yeast Candida pseudoglaebosa. We set out to understand how fungal diversity in S. purpurea pitchers changes over space and time, and how C. pseudoglaebosa might influence this diversity. In the summer of 2009, we assayed S. purpurea pitcher water fungal succession in Tom Swamp in Harvard Forest. We sequenced fungal DNA barcodes from 43 pitchers at different times throughout the growing season, and found that C. pseudoglaebosa has a strong impact on fungal diversity. It generally appears in pitchers early in succession, and once it arrives, it often becomes dominant quickly and decreases community evenness. We also identified two other culturable yeasts, Rhodotorula babjevae and Moesziomyces aphidis, which are common but not dominant in pitchers. In laboratory experiments, C. pseudoglaebosa outcompetes these two yeasts, but only if it is inoculated in large numbers, suggesting that C. pseudoglaebosa’s dominance is a consequence of early arrival during pitcher succession. The following summer (2010), we collected water from pitchers at five distant sites in the United States and Canada, and assayed fungal community diversity and C. pseudoglaebosa genetic diversity. We sampled pitcher plants from Tom Swamp in Harvard Forest, plus four other sites in British Columbia, Newfoundland, Georgia, and Florida (Floridian plants were Sarracenia rosea, a close relative of S. purpurea). Fungal communities tended to be structured geographically, with close communities resembling each other more than distant communities. In contrast, C. pseudoglaebosa exhibited three populations: one well-mixed population including isolates from Harvard Forest, Georgia, and Newfoundland (East Coast), one from Florida, and one from British Columbia. Taken together, these results suggest that C. pseudoglaebosa dispersal is not limited along the East Coast, but that there may be other ecological factors preventing mixing between Florida and the East Coast population.