Microbes are critical to plant health and drive biogeochemical cycles in all ecosystems. Therefore, understanding microbial community structure and functioning is of great importance for responding to environmental problems facing society today and in the future. I use microbial here in an expansive sense in this statement: meaning microscopic organisms, including archaea, bacteria, and even eukaryotes such as microalgae, fungi, and microinvertebrates. As a community ecologist who began my career studying invasive plants, I have expanded into considering microscopic ecosystems partly as model systems to understand processes in community ecology more generally, including invasion and trophic interactions.
I work at a range of scales, from viral genomes to landscapes, and using a variety of field-based, lab-based, and analytic methods, to investigate key questions in community ecology, such as:
1. What limits biological activity, particularly in cold and low-nutrient ecosystems, and how will that change as the climate warms?
2. How do processes of succession and invasion shape community composition, as opposed to the role of random chance?
Seasonal processes in the evolution of Arctic soils
I am currently a co-investigator on a collaborative effort to understand the unique role of extreme polar seasonality on the development of soil. As glaciers retreat due to a warming climate across the Arctic, they expose new soil that is typically very low in carbon, nutrients, and living things. Over time, bacteria, fungi, and microinvertebrates and algae grow and die in these sediments, developing the soil, and eventually plants move in. But the long polar night – which can be three months – followed by months of snowmelt – provide a uniquely challenging environment for microbial life, as well as unique opportunities for life. Our interdisciplinary team of geophysicists, engineers, modelers, remote-sensing snow scientists, geochemists, and biologists installed sensor arrays in the soil along a transect of soil age at the toe of a retreating glacier in Svalbard, Norway, last July to monitor the timing of temperature and liquid water at various depths. My role, as a biologist, is to sample the total DNA of potentially active organisms and the transcribed RNA of currently active organisms in the soil across four seasons within one year. Due to the global pandemic, fieldwork planned for this project in 2020 was been postponed to 2021, so the project has just gotten underway, and will provide vast amounts of bioinformatic data to continue digging deeper into the processes of microbial succession and activity for years to come. This project is supported by a joint award from the National Science Foundation and the UK Research Institute through the Signals in the Soil initiative, a grant from the Svalbard International Earth-Observing System, and a seed grant from CU Boulder’s Research and Innovation Office.
Microbial community assembly and function in Antarctic cryoconite holes
Cryoconite holes are small puddles that form in glacial surface ice when dust lands on it and the dark material absorbs sunlight, melting the ice beneath it. Entire ecosystems form and grow in these holes, with photosynthesizing algae and bacteria supporting microscopic animals such as rotifers and tardigrades (“water bears”). My postdoctoral work used these unique ecosystems as an system of “natural test tubes,” both to examine the patterns of biological diversity that form naturally in them, and to create them experimentally to learn the importance of random change relative to biological and physical processes. The fieldwork was carried out over the course of three austral summers from November to February of 2016-17, 2017-18, and 2018-19. I was fortunate enough to deploy to the ice for all three seasons. Laboratory processing has wrapped up, and although we have published several papers on our findings, the analysis and writing continues. Learn more about the project at the website I made for it (cryoholes.wordpress.com). This project was supported by the National Science Foundation’s Office of Polar Programs.
This explanatory mini documentary by Mark Fairbrother tells the story of the project and our initial findings. It is dedicated to Diana Nemergut (1974-2015), who originally led the funded award, and who is deeply missed.
Effects of an invasive grass on the Sonoran Desert
In my doctoral research, I studied how predation and resource competition interact to determine species diversity, especially in the case of species invasions. I specifically focused on how buffel grass (Pennisetum ciliare), which had been introduced from Africa to North America, suppresses the regeneration of long-lived native plants where it spread. I looked at whether the adult grass prevented native seeds from germinating and seedlings from establishing, and whether it did so through resource competition or through increasing the abundance of rodents that eat native seeds. The rodents eating native seeds in areas that buffel grass invades, however, act not only as consumers, but as seed-dispersers by burying them in shallow caches outside their burrow. To find out whether the rodents were burying seeds more often under buffel grass because its dense canopy provided better hiding places from owls, I used fluorescent powder to locate caches. Finally, I asked how the cover-seeking behavior to avoid predators might affect the diversity of the rodents themselves, especially if grass cover increased their effectiveness at hiding. Since there were no robust theoretical predictions for this, I used simple consumer-resource models to determine when predator avoidance behavior would increase or decrease the ability of the avoiders, who also compete for resources, to coexist. This project was supported by the Western National Parks Association, Garden Club of America’s Award in Desert Studies, and the Graduate and Professional Student Council’s Research Grants.