PS 12-165 - Seed germination of endemic Rhododendron carolinianum is facilitated by mycorrhizal fungi of its widespread confamilial Kalmia latifolia: Implications for migration and ex situ conservation

Monday, August 7, 2023

5:00 PM – 6:30 PM PDT

Location: ESA Exhibit Hall

Presenting Author(s)

DL

Daun Lee

Dept. of Biological Sciences, Smith College, Northampton, MA
Northampton, Massachusetts, United States

Coauthor(s)

VG

Virginia A. Griswold

Smith College, United States
JB

Jesse Bellemare, M.F.S., Ph.D.

Associate Professor
Dept. of Biological Sciences, Smith College, Northampton, MA
Northampton, Massachusetts, United States

Abstract: Climate change poses a major threat to biodiversity, especially for small-ranged endemic plants that might have limited migration ability. These challenges could be compounded for species with specialized mutualisms: if key partners are absent in new regions, range shifts could be slowed or halted. Many plant species in the Ericaceae benefit from mutualisms with ericoid mycorrhizal (ERM) fungi, which can enhance their ability to grow on acidic, nutrient-poor soils; however, the level of specialization in these partnerships and their potential to affect migration and colonization ability is not well known. This experimental study explored whether small-ranged Rhododendron carolinianum (Ericaceae), an endemic woody shrub restricted to the southern Appalachian Mountains, can successfully partner with ERM fungi associated with its widespread and abundant confamilial plant, Kalmia latifolia. Using a series of mesocosm experiments, we tested seed germination and seedling growth rates of both R. carolinianum and K. latifolia with and without ERM-containing inoculum from K. latifolia populations in Massachusetts, ~1000 km north of the native range of endemic R. carolinianum. Twenty mesocosms per treatment were used, each containing ~500 mL of a bulk 50:50 mixture of coarse sand and soil organic horizon material from a forest area lacking ericaceous plants; to half of these containers, ~30 mL of ERM-containing inoculum from the base of K. latifolia was added (~5% of total volume). On average, germination of R. carolinianum seed was higher (12-16%) in mesocosms treated with K. latifolia ERM inoculum vs. controls in both trials to-date, significantly so in the Spring 2022 trial (69% vs. 53%, p < 0.01). Seed germination of K. latifolia also increased in mesocosms with its own ERM inoculum, significantly so in the Fall 2022 trial (33% vs. 21%, p < 0.01). Results for seedling growth rates were less clear, although R. carolinianum seedlings tended to show larger leaf sizes in mesocosms inoculated with K. latifolia ERM fungi. These findings suggest that the early life stages of R. carolinianum can benefit from interactions with novel ERM fungal partners hosted by its widespread confamilial K. latifolia. The results raise the possibility of indirect facilitation of establishment for the endemic R. carolinianum in new regions where confamilials are already present and hosting ERM fungi. The findings could also be relevant for designing successful ex situ conservation collections of rare endemic Rhododendron species or guiding future assisted migration efforts.