Tundra, Microbes and World Climate

O. Roger Anderson is a microbiologist at Lamont-Doherty Earth Observatory who studies bacteria, amoebas, fungi and other microorganisms. Lately he has been thinking about how tiny organisms that inhabit the vast northern tundra regions could contribute to changing climate, since, like humans, they breathe in oxygen and breathe out carbon dioxide. Recently, Anderson found a way to estimate the volume of each amoeba along with that of other microbes, to model and predict the organic carbon content of the entire community, including its output of carbon dioxide. He is now applying this technique to estimate microbial CO₂ emissions as the tundra warms. He has published extensively on this topic, including a chapter in the new book, “Tundras: Vegetation, Wildlife and Climate Trends.” He spoke recently with journalist Kim Martineau.

How much carbon is stored in the tundra?
About a third of the carbon in Earth’s atmosphere —most of this organic matter is frozen within layer upon layer of dead mosses in the permafrost.

How small are these organisms, and what role do they play in the arctic?
Micron-sized bacteria are the smallest and most abundant microorganisms at the base of the food web — billions are in each pea-sized portion of tundra soil. Imagine spreading peas over millions of square kilometers, to a depth of a meter or more –that’s how much bacteria lies in the tundra. Other microbes include protozoa–amoeba, ciliates, flagellates–and fungi—yeasts and molds—in the hundreds of thousands per cubic centimeter.

Yeast is one microbe you study. What does this common ingredient in baked bread have to do with global warming?
Yeast in small quantities causes bread to rise by releasing relatively large amounts of CO₂. They are activated by warmth, nutrients (such as sugars) and water. As the tundra warms, permafrost melts to deeper layers each year. Fungi and other microorganisms become more active—in numbers and in intensity, releasing CO₂. Normally, the system is a net sink —plants take up the microorganisms’ released CO₂. But with tundra warming, more microorganisms may produce CO₂. The question is: will the plants keep up?

Has anyone documented a net flux of carbon dioxide from the tundra and how is it done?

A network of towers tracks carbon dioxide concentrations. In late summer, a net release of CO₂ occurs in some locations when plant growth is slowing but the microorganisms remain active; they even release CO₂ during winter, buried in snow. On a larger scale, it hasn’t tipped to a net efflux. That could change if substantially more permafrost melts.

You work with soil samples air-shipped from Toolik Lake, Alaska. What do you do with them in the lab?

I culture the microorganisms, measure them and apply my model to predict possible increases in microbial efflux of CO₂ with varying temperature and moisture conditions – a methodology I developed working first with mossy soils on the Lamont campus, similar to soils in the tundra. In the process, we also discovered dozens of new species using electron microscopy.

Methane is another greenhouse gas released when tundra thaws. Which is the greater threat for climate—methane or carbon dioxide?
Methane is a more potent greenhouse gas, released by methanogenic bacteria that consume carbon dioxide and release methane, especially if permafrost melting produces swampy, anoxic conditions. Other areas might become drier, and a larger carbon dioxide source. Currently, CO₂ seems to be the greater concern.

What sparked your interest in microbiology?
I received a small microscope for Christmas when I was six years old and developed a life-long fascination for the complexity of microbial communities and their ecology.

Do you have a favorite microorganism?
I have to confess that I still find radiolaria most remarkable. A snail’s shell hardly compares to the radial, lacy-like structures radiolaria produce. We now understand how the cytoplasm creates these structures, but not the genetic control. Understanding that would lead to a breakthrough in cell biology.