It’s amazing to me that anything can live in the soils of the Dry Valleys. Even now, during the height of summer, conditions aren’t exactly cushy: soil temperatures on a warm day hover around 50 degrees F, the soils are very salty, and the availability of liquid water is patchy at best. Walking across the rough, rocky surface, it’s no wonder that early explorers and scientists declared the Dry Valleys devoid of life. And I haven’t even mentioned the winter – complete darkness, extreme cold, everything frozen solid.
So how do they do it? How do we find living creatures in so many of the samples we collect? The animals living in these soils must be able to cope with indefinitely long periods without water in the frigid cold, but must also be able to react quickly to the presence of running water. They do so by going into anhydrobiosis, a state in which they are freeze-dried. All bodily functions stop (no eating, breathing, or reproducing) and remain on hold until conditions improve. While organisms in anhydrobiosis certainly appear dead, just add liquid water, and they’ll be squiggling around in no time!
If these organisms have no trouble with extreme cold and extreme dry, what can stop them? For ecosystems everywhere – not just the harsh environment of the Dry Valleys – scientists like to know what limits life; we like to define the limiting nutrient. Imagine you’re baking a huge batch of chocolate chip cookies – as many cookies as possible. As you keep mixing batches of cookie dough, one ingredient is bound to run out first. Maybe it’s the chocolate chips. You have plenty of flour, sugar, and eggs, but what’s a chocolate chip cookie without the chocolate chips? The same thing happens in an ecosystem, only with nutrients instead of ingredients. There are many nutrients that are necessary for life, and if any of them are in short supply, then life is severely limited.
What’s the limiting nutrient in the Dry Valleys? Well, it depends. First of all, there aren’t a lot of any ingredients to start with. In Taylor Valley, the limiting nutrients changes as you head up the valley. Near the ocean, near Lake Fryxell, nitrogen is a limiting nutrient. Up at the top of the valley, near Lake Bonney, phosphorus limits life. In fact, Lake Bonney is one of the most phosphorus-limited ecosystems in the world! As I’ll explain in a future blog post, I’m interested in why the amount of phosphorus varies so much across the valley.
Knowing the limiting nutrient in an ecosystem allows us to predict what will happen with any changes. How will life respond if more nutrients enter the system (something that may happen due to a warming climate)? We can test our predictions by artificially adding nutrients (like phosphorus and nitrogen), and then seeing what happens. To judge the response, we record things like nematode abundance and soil respiration, a measurement of the activity of organisms in the soil.
Now you get to make some predictions. What will happen near Lake Fryxell if we add nitrogen? What about phosphorus? And what will happen near Lake Bonney if we add nitrogen? What about phosphorus? Do you think these responses would continue forever with more and more of the added nutrient?