Monday, December 22, 2008

Measuring soil micro-organisms

Soil in the dry valleys of Antarctica is a hard place to live. It is very cold and very dry. There's not a lot of water available, and most of it is frozen. There's also not a lot of food to eat. But, believe it or not, there are organisms that can live in such a harsh environment. The organisms living in the soil here are all microscopic. That means they are too small to see with your naked eye. But, they are definitely there! We are interested in studying how these organisms change the nutrients in the soil. It's important to know how they change the nutrients because these nutrients are needed by all living things.

Because the soil organisms are so small, it's very hard to study what they do. You can't watch them individually unless you remove them from the soil and look at them under a VERY powerful microscope. So we have to use other ways to measure what the micro-organisms are doing.

One of the ways we measure what organisms do is by measuring their respiration. When living things (including people) breathe, we exhale carbon dioxide. If we're sitting still, we breathe very slowly and exhale small amounts of carbon dioxide. If we are very active and run around a lot, we breathe faster and exhale more carbon dioxide. A whole classroom of people running around can exhale more total carbon dioxide than just one person. So, more carbon dioxide is exhaled by larger numbers of more active organisms.

The soil micro-organisms in Antarctica work the same way. If we measure how much carbon dioxide is being produced in the soil, we can guess how many micro-organisms there are and how active they are. More carbon dioxide being produced would mean there are more active micro-organisms.

We have a fancy machine that helps us measure carbon dioxide in the soil. We nest it over the soil, and it measures how fast the amount of carbon dioxide changes over that patch of soil. It's called an IRGA. Here's me using it:
I am interested in knowing how the amount of carbon dioxide changes if you change the amount of water in the soil. So, I've been measuring carbon dioxide near the lake, where the soil is very wet. As I move the machine farther from the lake edge, the soil gets drier. So by moving the IRGA farther and farther from the lake each day, I am finding out how carbon dioxide respired by micro-organisms changes from wet to dry soil. In this picture, I'm making a measurement pretty close to the lake edge. Today, we moved it several meters farther back, where the soil is less wet. Tomorrow, we will move it even farther away where the soil is very dry. From the information we collect, we will know much is being breathed out by the soil micro-organisms as you go from wet to dry soils. That will let us estimate how many organisms they are and how active they are.

That is one of the ways we measure soil micro-organisms. There are many other things we do to measure what's living in the soil, but that will have to wait for another post!