Plants, fungi, and freeloaders: examining temporal changes in the “taxonomic richness” of endophytic fungi in the dwarf mistletoe Arceuthobium americanum over its growing season

Abstract

Arceuthobium americanum Nutt. ex Engelm. (lodgepole pine dwarf mistletoe) is a dioecious plant parasitizing conifers in North America. Here, we documented changes in the “taxonomic richness” of culturable endophytic fungi in male and female A. americanum over the growing season. Endophytic fungi were isolated from vegetative stems of surface-sterilized aerial shoots from male and female A. americanum collected weekly from April to September. Isolated fungi were characterized macroscopically, generating a database of 48 morphologically unique forms that likely represented individual taxa. A random sample of endophytic fungi was sequenced to determine identity based on ITS rDNA. Richness increased throughout the growing season similarly in the stems of both sexes, suggesting that increased developmental age or time in the environment facilitates an increase in endophyte richness: male and female endophyte communities were 91% similar based on Sorensen’s coefficient. Sequenced endophytes came from many diverse taxa, including Serpula, Alternaria, and Tremella, which may function as mutualistic symbionts within the mistletoe. An increase in fungal richness throughout the growing season has been observed in all flowering plants examined to date, although our observation is the first for the genus and for parasitic plants in general, and has also contributed to knowledge of fungal diversity in dioecious plants.