UC Santa Cruz

Soil microbial communities play critical roles as decomposers, plant pathogens, and plant mutualists in terrestrial ecosystems. Understanding how these communities will respond to a changing environment requires well-replicated studies across diverse ecological contexts and a careful assessment of the methodological dependencies of large-scale microbiological research. In my dissertation, I develop methods for the study of soil microbial communities across three registers: informatic, ecological, and anthropological. First, I present a software package to facilitate access to an open-access, continental-scale dataset of soil microbial DNA metabarcoding sequences for ecological research (Chapter 1). Second, I use this dataset to predict the spatial distributions of fungal taxa across the U.S. and Canada and quantify the sensitivity of soil fungal community composition to ongoing climate change (Chapter 2). Finally, taking an ethnographic approach, I observe how soilborne plant disease comes to be known through a variety of scientific practices that stabilize distinct objects of study (Chapter 3). Together, this work illustrates that while soil microbial communities everywhere may be shifting, these shifts are not the same everywhere. The North American boreal forest occupies a particularly precarious climate in which even slight warming can create major shifts in the composition of its soil fungal communities. Additionally, the enrollment of soil microbial communities in the transition to post-fumigant agriculture contributes to a complex political terrain wherein the possibilities for knowing soil microbial communities are entangled with the possibilities for managing soilborne plant disease. By showcasing diverse methods for studying soil microbial communities, this dissertation puts forth an ontological approach to scientific inquiry that does not presuppose objects as a given but rather enacts them anew through methodological innovations.