Honors Theses

Date of Award

5-2026

Document Type

Undergraduate Thesis

Degree Name

BS

Department

Biology

Faculty Mentor

Jeremiah Henning, Ph.D.

Advisor(s)

Juan Mata, Ph.D. and Jason Strickland, Ph.D.

Abstract

Salinity stress is increasing in coastal and estuarine ecosystems due to increasing temperatures and the reduction of freshwater inputs via precipitation pattern changes. Elevated salinity can negatively affect plant survival, threatening the stability of coastal wetlands and the ecosystem services they provide. Juncus roemerianus is a common and dominant marsh plant in the Northern Gulf Coast that lives in varying salinities. Growing evidence suggests that root-associated fungal endophytes may contribute to enhanced stress tolerance; however, the response of fungal communities to salinity remains poorly understood.

This study evaluated how salinity influences the abundance and diversity of culturable root-associated fungal communities within Juncus roemerianus. To quantify endophyte communities that emerged from Juncus roots, we placed in-tact roots of Juncus roemerianus plants directly onto malt extract agar media amended with 0, 20, or 40 ppt salinity to represent freshwater, moderate, and high salinity conditions. We monitored fungal growth emerging from the roots over a seven-day period and measured total fungal abundance and diversity of unique fungal morphotypes across the salinity gradient. Overall, we observed emergence of thirteen fungal growth across all salinity treatments; however, morphotype richness declined significantly between 0 and 20 ppt, and morphotype composition shifted across the salinity gradient. These patterns were likely driven by the loss of salt-sensitive morphotypes and increased growth of salt-tolerant taxa. Additionally, total fungal abundance exhibited a non-monotonic response, with lowest abundance at 20 ppt and highest abundance at 40 ppt, indicating dominance of salt-tolerant taxa at high salinity. High salinity treatments generally exhibited lower fungal diversity and altered morphotype distribution compared to lower salinity conditions, indicating that salinity acts as a selective pressure on root-associated fungal communities. Understanding how fungal endophytes respond to salinity provides insight into the factors that shape plant-microbe interactions and may inform future restoration strategies that consider microbial contributions to plant resilience into increasingly saline ecosystems.

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