Faculty Profile: Alexander Barron

Biogeochemist

Departments of Biology and Chemistry, Carleton College

Jump down to Teaching * Research * Connections between teaching and research

Teaching

What are your teaching responsibilities?

I am a visiting lecturer for the year, teaching Ecosystem Ecology and a non-majors Global Change Biology course in the Biology department and Principles of Environmental Chemistry in the Chemistry department. I've also helped to advise Biology and Geology majors on their comprehensive exercises (senior theses).

How does your teaching relate to traditional geology?

I take an earth systems perspective in all of my courses. My tendency is to see the world as one big biogeochemical system where chemical and energy fluxes link the biological components to the oceans, soils and atmosphere. I try to teach students to think in terms of cycles, like the carbon cycle. One of my new favorite course readings is Primo Levi's short story "Carbon," which follows a carbon atom on a trip through space and time.

How does it take geoscience in new directions? How does it take your department in new directions?

Although my classes are outside of the geology department, I link to geoscience in both directions. My hope is that ecology and chemistry students learn how soils and the atmosphere can have big impacts on their fields while the geologists further appreciate how ecological, chemical and evolutionary forces help to shape everything about our planet.

One thing I noticed in teaching Environmental science courses this year is that students are deeply concerned about climate change but underinformed. The research out there is not in a digestible form, and both skeptics and environmentalists cloud the issue. I think that global change, and the cross-disciplinary perspectives it requires, will continue to grow as a subject of study, both in and beyond the classroom.

Research

What are your research interests and activities?

I am interested in fundamental ecosystem processes and how they are affected by anthropogenic disturbance. I use concepts from physical chemistry and the geosciences (stoichiometry, thermodynamics, systems approaches, etc.) to gain insight into forest ecosystem functioning and how it will change under the pressures of global change.

My thesis research focuses on the controls over nitrogen (N) fixation in tropical forest ecosystems. Nitrogen fixation (the conversion of atmospheric N2 gas to plant available ammonia), although a critical nitrogen input to many ecosystems, is poorly understood ecologically. This is troubling at a time when human beings have doubled the annual nitrogen inputs to the terrestrial environment and nitrogen fixation is needed to grow crops and restore ecosystems. I have used my thesis to examine the patterns of nitrogen fixation of both leguminous (bean family) trees and soil bacteria in lowland tropical forests as well as the soil nutrient dynamics that control them.

How does your research relate to traditional geology?

Soil formation is a function of climate, organisms (plants and microbes), topography, parent material (bedrock), and time. Geology typically focuses on climate, topography, bedrock, and time; I look at how nitrogen fixing plants can alter the soil chemistry and fertility by bringing in new nitrogen.

Here's why that's interesting: if you consider the carbon cycle, terrestrial plant uptake is one of the major fluxes. But why don't plants grow more than they do? There's plenty of carbon available. But, even with plenty of light and water, plants also need nitrogen to build plant tissue. It turns out that nitrogen is the limiting factor for plant growth in many ecosystems and that a shortage of nitrogen may prevent plant uptake of elevated CO2, making climate change more severe.

However, there are some plants (nitrogen fixers) that can make their own nitrogen. More accurately, bacteria in the plants' roots use an enzyme to split N2 to make ammonia. (The bacteria get carbon from photosynthesis in exchange for the nitrogen they produce.) Why should nitrogen limit plant growth when there are plants that can make their own nitrogen when they need to? It seems that the cost of fixation and other factors -- including the availability of phosphorus and molybdenum -- limit how much nitrogen the plants can make. And that all has an effect on the fertility of the soil, and on how quickly an ecosystem can respond to disturbances such as deforestation and global climate change.

How does it take geoscience in new directions? How does it take your department in new directions?

In exploring nutrients that limit rates of nitrogen fixation, my colleagues and I have been able to document the importance of molybdenum to biological nitrogen fixation in the tropics. This result suggests we need to take a much closer look at how weathering and soil conditions may impact the ability of plants and microbes to run enzymatic processes. When humans clear tropical forests, the soil loses a ton of nutrients, especially nitrogen. Because tropical forests are gigantic carbon pumps, the rate at which those nutrients are replenished will impact the carbon cycle, which will obviously affect how much CO2 is in the atmosphere. If soils are molybdenum poor, fixation may restore the lost nitrogen at a much slower rate. The result is a biologically mediated link between climate change and soil chemistry.

Connections Between Teaching & Research

How does your teaching influence your research? How does your research influence your teaching?

Teaching some aspect of global climate change to a mix of majors (both science and otherwise) each term has helped to emphasize for me the importance of ecosystem research and pushed me to think about research questions that more directly interact with policy. I also tend to approach my research from a teaching perspective: what would I want to know if I were watching myself give a lecture on this?

I use my experiences and photos from Panama, Kenya and Hawai'i frequently to set the stage for concepts in class. It's a nice bit of motivation to think that your chemistry class might one day lead to adventures in the rainforest.