Thomas Bytnerowicz is our third Stengl-Wyer Scholar this year. He studies the feedbacks between global change and nitrogen and carbon cycling. As part of the Stengl-Wyer Endowment, the Stengl-Wyer Postdoctoral Scholars Program provides up to three years of independent support for talented postdoctoral researchers in the broad area of the diversity of life and/or organisms in their natural environments.
I interviewed Tom to learn more about his work and discovered some facinating things about forests.
Tell us where you came from before UT, and what you studied then.
My involvement in science started in high school assisting with research on plant-soil interactions in the face of changing fire regimes and nitrogen deposition in Southern California’s Joshua Tree National Park. I then worked in a handful of research groups before graduate school, ranging from atmospheric chemistry to aquatic plant ecology. I received a BS in Environmental Chemistry from UC San Diego and then went to Columbia University for my PhD in Ecology and Evolutionary Biology. At Columbia I studied the factors determining the variation in nitrogen fixing tree abundance and function across latitude, with Duncan Menge. This work included methods development for measuring nitrogen fixation, theoretical modeling and statistical analysis of forest inventory datasets to better understand the successional trajectories of nitrogen fixing trees, and experimental work determining the temperature response of nitrogen fixation and the timescales over which nitrogen fixers can turn on and turn off nitrogen fixation.
What got you interested in studying feedbacks between global change and nitrogen and carbon cycling?
I have always been fascinated by plants, and when I learned about how nitrogen fixing trees can bring massive quantities of new nitrogen into ecosystems, thus stimulating forest growth, I was hooked. I was first introduced to active research on this subject by attending presentations at the 2012 Ecological Society of America annual meeting in Portland. I thought that it was so cool that this process, a major determinant of nitrogen limitation and cycling in ecosystems, is biologically mediated. This means the quantity of nitrogen in ecosystems is dependent on individual plants that experience evolution, competition with neighbors, cooperation with their symbiotic bacterial partners, and other ecological processes. I really enjoy thinking about all those things as well as what role nitrogen fixation plays on the structure and functioning of the world’s ecosystems. Nitrogen fixation is directly tied to the future of the land carbon sink, and thus the trajectory of climate change, as the ability of forests to take up the additional carbon dioxide that we emit into the atmosphere relies on nitrogen not limiting plant growth. A big question that comes from this, and one that I am trying to address with my research is: Will nitrogen fixation increase or decrease with climate change and what effect that will have on the trajectory of climate change? This is how my research addresses the feedbacks between global change and nitrogen and carbon cycling. All three are linked in my research, as nitrogen fixation affects forest growth, which affects the uptake of carbon dioxide from the atmosphere, which affects climate and therefore temperature and precipitation patterns, which in turn affect nitrogen fixation.
A nitrogen fixing tree (a Robinia pseudoacacia sapling) on the left and R. pseudoacacia root nodules on the right.
Illustration of system Bytnerowicz developed for making coupled measurements of whole-plant nitrogen fixation and carbon exchange (Bytnerowicz et al. 2019 Methods in Ecology & Evolution)
How do field labs like the ones at UT figure into your work?
Field labs such as Brackenridge Field Laboratory provide the greenhouse space to conduct large experiments on potted plants as well as an opportunity to study naturally growing mesquite trees on the property. Texas is unique in that it has one of the highest relative abundances of nitrogen fixing trees in the world, which is very exciting for someone who studies nitrogen fixation. I also feel like I will not take the opportunity to do greenhouse experiments for granted, as I did my PhD in New York City, where such work was close to impossible to do as a result of the scarcity of greenhouse space in the city. I am grateful that that is no longer a limiting factor for my research, as experiments in such settings are critical to the empirical side of my work.
Where do you see your research agenda heading here at UT?
As a Stengl-Wyer Fellow, I plan to study the complex interactions that environmental conditions and competition with neighboring trees have on the success of nitrogen fixing trees and in turn what effect nitrogen fixing trees are having at scales ranging from their local community to the entire globe. I will do this through a combination of modeling and empirical approaches, with the assistance of my Stengl-Wyer hosts, Amy Wolf and Caroline Farrior. This work will improve our understanding of why nitrogen fixing tree abundance varies spatially across biomes, how it may shift with climate change, and what that means for nitrogen inputs and carbon uptake by forests.
