My lab (http://beverlab.ku.edu) studies plant-microbe interactions. One important interaction we work on is the mycorrhizal symbiosis. This symbiosis is a typically beneficial relationship between plant roots and fungi (the mycorrhizal fungi) that occurs in 80-90% of plants around the world. These fungi are primarily known for enabling greater nutrient supply to their plant host, but also help with water uptake, soil aggregation, and even pathogen defense (https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecy.1892)!
My primary field work is in Ecuador, both in the mainland and the Galapagos. The focus of this work is to test whether native plants experience a mycorrhizal filter as they disperse from the mainland to the island and to understand the consequences of novel plants and microbes for the native flora. We hypothesized that the lack of microbes on this oceanic island will skew the initial colonization by plants, to be less mycorrhizal, since those species are able to establish without these mycorrhizal partners. We call this filtering out of non-mycorrhizal species the mycorrhizal filter. We further hypothesized that human-introduced secondary colonizers, the naturalized species, would result in a flora with a greater proportion of mycorrhizal plant species. This is because these naturalized species are commonly agricultural plants brought with soil, including their symbionts, and may overcome the mycorrhizal filter the native plant experience.
My initial trip to the Galapagos in 2017 for my dissertation work.
My advisor and I started wondering if this pattern could hold across islands and mainlands in general. We started collecting plant species checklists from a few islands around the world to answer this question. As I was doing this research, I found several studies by Patrick Weigelt and Holger Kreft using global datasets of plant species checklists. Not only did these authors have global checklists that included thousands of mainland and island ecosystems, but they had these lists for native and naturalized plant species! We decided to contact these authors to see if we could work together. Although we have never met in person, working with this group has been a great experience. Having thirteen coauthors means a lot of feedback, which can be overwhelming. Nonetheless, this large group brought many perspectives to the paper. The statistical analysis, the background knowledge about the dataset, and writing of paper heavily benefited from this large group effort.
Many rounds of reviews later, we knew these were exciting results. Islands are different. The proportion of mycorrhizal native plant species was higher on mainlands than on islands. For naturalized species, this relationship flipped, with islands showing a greater proportion of plant species that were mycorrhizal. We even found that distance had an important impact on native island colonizers; with greater distance of islands from a mainland source, the proportion of plant species that are mycorrhizal declines. The mycorrhizal filter is real. This means that from a management perspective, mycorrhizal fungi are not always beneficial to native plants. In mainland systems, mycorrhizal fungi are generally seen as beneficial to native plant species and inoculation with mycorrhizal fungi has been shown to help in restoration of native plant species. This may not be true in islands as the native plants tend to be less mycorrhizal. In addition, in terms of preventing invasion, the emphasis is different on mainlands than on islands. Although most non-native plants on both mainlands and islands are mycorrhizal, invasion risks in mainlands are predominately non-mycorrhizal plant species, while on island they are mycorrhizal species. Mycorrhizal fungi shape global plant biogeography.
Figure 1. of our paper, showing (a) the major patterns of proportion mycorrhizal plant species in both native and naturalized mainland and island floras. The maps (b) show the distribution of native and naturalized regions used in the study.
Now, I’m spending a year in Ecuador, using specific species and field data to build on this initial work. We hope to understand differential mycorrhizal response of plant species found on the mainland and island (native and naturalized). This work also aims to uncover the differential impact of mycorrhizal fungi on plant growth from the mainland and the island. Finally, we are investigating the possible evolution of mycorrhizal response of native island plants once they begin interacting with introduced species and their novel microbes. Ultimately, we hope this work will build on this global analysis to continue improving our knowledge of plant invasions and to inform management.