Measuring Biotic Activity

Today, Julia and I went to the Lake Bonney basin to take some measurements on the stoichiometry plots. This is the experiment I posted about a couple days ago, where we add carbon, nitrogen, and phosphorus to the soil to see how it influences soil organisms and nutrient cycling. We do this experiment at two locations: Lake Fryxell basin (where I posted from before) and Lake Bonney basin (where we were today). We use these two sites because they naturally have very different nutrient conditions. Bonney has a lot more nitrogen, and Fryxell has a lot more phosphorus. That means that the two sites might respond differently to the nutrient additions, which would be very interesting!

One of the ways we measure the response of the biota is by measuring carbon dioxide flux. When most soil organisms respire, they produce carbon dioxide (abbreviated CO2). Humans do this when we breath, too. We breath in oxygen and breath out CO2. Soil organisms, from bacteria to nematodes, also respire to produce CO2. By measuring the amount of CO2 coming out of the soil, we are measuring how much the soil organisms are respiring. We hope to see an increase in respiration when we add nutrients (specifically, more respiration when we add C and P to Bonney and when we add C and N to Fryxell).

After adding the nutrient treatments to the plots like we did a few days ago, we go back and measure CO2 flux. We do this using a machine called an Infrared Gas Analyzer (abbreviated IRGA. It is made by a company called LI-COR, so we usually call the machine the LICOR). Here's Julia learning to use the LICOR: This is a fancy, expensive machine (about $25,000 for the whole set-up) that nests over the soil and sucks air from the space just above the soil. That air is sent through the tubing to the yellow box, which contains the IRGA. The IRGA measures how much CO2 is in the air space above the soil and how much the concentration of CO2 changes over one minute. If the soil organisms are respiring, we will see an increase in CO2 in that air space at a certain rate, called the "CO2 flux". We hope to see a bigger flux rate when we add nutrients.

We finally had a day of nice weather in the field, so we were not delayed for once! We are back in the lab now at McMurdo processing more of our soil samples from these stoichiometry plots. We head back to the field on Thursday, hopefully to visit a penguin rookery!