Date of Award

5-2026

Document Type

Thesis

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Lopez, Lua

Abstract

Invasive species cause significant damage to ecosystem biodiversity and can cost billions of dollars to restore native species (Van der Wal et al, 2008; Diagne et al., 2021).  In certain instances, even if the invasive species are removed, they can leave legacy effects on the environment that make restoration more challenging (Conser and Connor, 2008; Elgersma et al., 2011). Carpobrotus edulis is an invasive species of plant that is known to cause changes to its environment such as affecting the soil nitrogen cycle and the pH, potentially leading to persistent changes in the soil microbiome and causing native species to be unable to reestablish even after removal of the invasive plant (Vieites-Blanco and González-Prieto, 2018). This study aimed to assess whether C. edulis invasion is associated with changes in soil microbiome composition, compared to non-invaded sites. We hypothesized that invaded soils would exhibit distinct and potentially less diverse microbial communities due to altered soil conditions, and that these changes may favor microbial groups that negatively impact native plant survival.

We analyzed soil samples from three different sites by sequencing the DNA of bacteria and fungi present in the soil. We used Alpha and Beta diversity indices to determine if there were differences in diversity between invaded and uninvaded sites and to compare diversity of site replicates.

Overall, we found there was a decrease in biodiversity of the microbiome in invaded sites compared to uninvaded sites. Bacterial communities had a more consistent trend between sites compared to fungal communities.  Because these patterns were not entirely consistent across all sites and replicates, this indicates that local environmental factors also play an important role in shaping microbial communities. While invasion introduces detectable shifts in community structure, these effects operate alongside strong site-specific influences, resulting in both consistent trends and localized variation across replicates.

When looking at the functionality of the microbial taxa that were affected by invasion, we found that C. edulis caused shifts in both bacterial and fungal communities that are likely to have an overall negative impact on native plant survival. The reduction of beneficial microbial groups involved in nutrient cycling and plant symbiosis, combined with an increase in disturbance-adapted and potentially less beneficial taxa, may create soil conditions that hinder native plant establishment and facilitate continued invasion.

This study demonstrates that Carpobrotus edulis invasion is associated with significant shifts in soil microbial communities, with clearer and more consistent effects observed in bacterial assemblages than in fungal communities. Our findings prompt the need for addressing both restoration of native plants to the invaded sites as well as restoring native microbial communities that support them.

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