Microclimate is a strong predictor of the native and invasive plant-associated soil microbiota on San Cristóbal Island, Galápagos archipelago

Understanding the major drivers that influence soil bacterial and fungal communities is essential to mitigate the impacts of human activity on vulnerable ecosystems, like those found on the Galápagos Islands. Located ~1000 km off the coast of Ecuador, the volcanically formed islands are situated within distinct oceanic currents, which provide seasonal weather patterns and unique microclimates within small spatial scales across the islands. Although much is known about the impacts of human activity, such as climate change and invasive plant species, on above ground biodiversity of the Galápagos Islands, little is known about the resident soil microbial communities and the drivers that shape these communities. Here, our goal was to investigate the bacterial and fungal communities found in soil located in three distinct microclimates: Mirador (arid), Cerro Alto (transition zone), and El Junco (humid), and associated with native and invasive plant types. At each site, we collected soil at three depths (rhizosphere, 5 cm, and 15 cm) associated with the invasive plant, Psidium guajava (guava), and native plant types. We determined that the sampling location (microclimate) was the strongest driver of both bacterial and fungal communities (74 and 38%, respectively), with additional minor but significant impacts from plant type and soil depth. This study highlights the continued need to explore microbial communities across diverse environments and demonstrates the weight of different abiotic and biotic factors impacting soil microbial communities across San Cristóbal Island in the Galápagos archipelago.IMPORTANCE/SIGNIFICANCEHuman activity such as climate change, pollution, introduction of invasive species, and deforestation, poses a huge threat to biodiverse environments. Soil microbiota are an essential component to maintaining healthy ecosystems. However, a greater understanding of factors that alter these microbial communities is needed in order to find ways to mitigate and reverse the impacts imposed by human activity. The Galápagos Islands are a unique real-world laboratory, in that the islands’ biogeography and physical locations in the Pacific Ocean provide distinct microclimates within small geographic distances. Harnessing these distinct environments allowed us to investigate the influence of microclimates, soil depth, and vegetation cover on bacterial and fungal community composition.