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Publication Date

2023-5

First Advisor

Jesse Bellemare

Document Type

Honors Project

Keywords

Rhododendron carolinianum, Kalmia latifolia, endemism, ericoid mycorrhizal fungi, mutualism, climate change, assisted migration, conservation, species range limits, germination

Abstract

Climate change poses a major threat to biodiversity, especially for small-ranged endemic plants that might have limited ability to migrate. 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 family 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 and exclusivity in these partnerships is not well known. This experimental study explored whether small-ranged Rhododendron carolinianum (Ericaceae), an endemic restricted to the southern Appalachian Mountains, can successfully partner with ERM fungal inoculum associated with a 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 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 (~6% of total volume). Mean germination of R. carolinianum seed was greater 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). Effects on seedling growth rates were less clear, although R. carolinianum seedlings tended to show larger leaf sizes in mesocosms inoculated with soil containing ERM from K. latifolia. These findings suggest that 3 the early life stages of R. carolinianum can benefit from interactions with novel inoculum, likely containing ERM, hosted by its widespread confamilial K. latifolia. The results raise the possibility of indirect facilitation of establishment for endemic R. carolinianum in new regions where confamilials are already present and hosting ERM fungi. The findings are also relevant for planning ex-situ conservation collections or future assisted migration efforts.

Rights

©2023 Virginia Griswold. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

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