Stoichiometry

This morning, Katie and I flew to the Lake Bonney basin for another two days of field work.
While we are here, we will be working on a project that will tell us how the soil and soil organisms respond to nutrients added to the soil.

There are three main elements that are very important for life everywhere: carbon, nitrogen, and phosphorus. These nutrients are important for all organisms to grow and live. If one of these elements is in short supply, organisms cannot continue to grow. So, the amount of nutrients in the soil can be limiting to life. We want to know which of these elements are limiting to life in the dry valleys.

We have set up areas where we add carbon, nitrogen, and phosphorus to the soil. Each year, we add more of the nutrients and measure how the microbes and invertebrates living in the soil respond to the additions. We add the nutrients by dissolving sugar and salt in water, then pouring the water over the plots. Some plots get sugar water (for carbon), some get water with nitrogen or phosphorus salt added, and some get both sugar and salt. In this photo, Breana is adding some nutrient water to one of the plots.

We use the plastic cone to prevent the wind from blowing the water away before it reaches the ground. Or, you can be like Uffe and wear the cones as a hula skirt:
After we add the nutrients, we measure respiration to see how active the microbes are. We also measure the amount of nematodes in the soil and how the soil chemistry changes after the nutrients are added.

We've been working on this project for many years. So far, we have learned that carbon is most limiting to life in the dry valleys. Carbon in the soil mostly comes from photosynthesis by plants. Plants are able to take carbon from the air (as carbon dioxide) and turn it into forms usable by soil organisms. Because Antarctica is so cold and dry, there are not a lot of plants. We only have some mosses and algae that can photosynthesize, and they are only found near sources of water. Because there's not a lot of photosynthesis, there is not a lot of carbon added naturally to the soil. So, carbon is often the limiting nutrient in the dry valley soils, which is why we notice the biggest response in the activity of the organisms when we add carbon.

Nitrogen and phosphorus may also become limiting in the soil, if there is enough carbon for organisms to use. That is why we look at all three of the nutrients. We want to know how increases in all three nutrients might influence soil organisms. Which nutrient is most limiting might not be the same everywhere in the dry valleys, since the different areas have different geology. Hopefully this project will be able to tell us which nutrients are limiting in the different areas.

Katie and I are only at Bonney through tomorrow, then it's back to McMurdo to process our soil samples that we collect here. Hopefully, the final member of our team will arrive tomorrow. Ross's flight should be arriving tomorrow afternoon as we're returning from the field. Let's all hope that the good weather continues!