On Tuesday, Ross and I got to do something very exciting: we recovered year-old soil incubation experiments (sausages) that we had buried last season. As we approached the site, I had no idea what to expect: would I be able to find them? What would the sausages look like? Would they be intact? I soon spotted the tags, started digging, and there were the sausages! Yes! They looked exactly the same as when we buried them! But hopefully we’ll be able to detect changes inside…
So what are these soil sausages, and why was I burying them last season and unburying them on Tuesday? Well, to answer these questions, I have to tell you about phosphorus. As you may remember from an earlier blog, phosphorus is one of the limiting nutrients in Dry Valley ecosystems, which means that there isn’t much of it available to organisms. All phosphorus that is available originally comes from the mineral apatite, found in small quantities in igneous rocks. So if we understand something about how apatite breaks down and releases phosphorus, we’ll know something more about how an important nutrient enters the system.
To study the weathering (or breaking down) of this important mineral, we put store-bought crystals of apatite into the soil sausages. The tubing holding the sausage together is permeable, so water and bacteria can still interact with the mineral surfaces. We buried the sausages in a wet area just outside a stream channel, where we know there is a lot of flowing water. Water is crucial for chemical and biological weathering – we wouldn’t expect much to happen in the dry soils that carpet the majority of the valley.
So what are we looking for? After I get back to Dartmouth, I will separate out the apatite crystals, and I’ll look at them under very strong microscopes. I’ll look for any signs of weathering – small grooves in the surface of the rock. I’ll also look for any signs of life – with these microscopes I may even be able to see bacteria clinging to the surface of the mineral! These signs will tell me how actively apatite is being weathered, and how quickly phosphorus can be released into the system.
Back at Dartmouth, I’ll also be looking at apatite grains from the soils themselves (i.e. not ones we put there). So far, I’ve been able to see some interesting patterns in the shapes of the grains. I’m looking forward to understanding more about phosphorus cycling in the Dry Valleys – this will be a project that I’ll be working on for a number of years, and it’s exciting to see it progress!
I’ve chosen to study phosphorus cycling in the Dry Valleys. After reading about the Dry Valleys and hearing about our research, what would you choose to study here? What would you be curious to learn about?