We did this experiment at two different places in the Dry Valleys: near Lake Fryxell and near Lake Bonney. Since the environment in both basins is so harsh for plant life, there's not a lot of carbon naturally in the soil. So, we hypothesized that both sites would be "carbon limited", meaning that if we add carbon to the soil, the soil organisms would be very excited to have the new food source and become a lot more active! Lake Fryxell and Bonney we think are both carbon limited, but we hypothesized that they would differ in whether nitrogen or phosphorus would stimulate the soil organisms. Lake Fryxell has a lot more phosphorus in the soil than Bonney, so we hypothesized that adding nitrogen would stimulate the soil biology more, because they already would have the phosphorus they need. Since Lake Bonney has more nitrogen than phosphorus, we hypothesized that adding phosphorus would stimulate the biology more, because they had the nitrogen they needed.
this post. We extracted all of the nematodes, tardigrades, and rotifers living in the soil, and we measured nutrients in the soil, too.
|Measuring respiration at the Lake Bonney experimental plots.|
So what did we find? For 3 years, we didn't see any change in the soil at all. The biology didn't respond to the added water or nutrients. But, then, after 3 years, we started to see a difference! Soil respiration was greater in the plots where we added carbon+nitrogen. That means that the soil microbes were limited by both carbon and nitrogen, and having more of those allowed them to be more active. It just took a few years for them to be able to adjust to use the extra resources! It's also interesting, because Bonney Basin was also stimulated by carbon+nitrogen, even though it already had plenty of nitrogen (or so we thought!). We also noticed that the total number of invertebrates and total amount of microbes in the soil didn't change. Only their activity changes. It's similar to the way that having a lot of candy makes you more active and respire more, even though there's still only one of you.
The increased activity with the nutrient additions means that future warming in the Dry Valleys that melts ice will have an impact on the soil organisms living there. But we also found that the stimulated activity was fairly short-lived, only lasting a few weeks, so it would take sustained pulses of water and nutrients to make a big impact on the soil organisms. A sustained pulse from melting ice is a likely scenario for the future of the Dry Valleys, so our experiment might tell us about the consequences of climate change for these soil organisms.
The results of this study are published in: Ball, B.A., B.J. Adams, J.E. Barrett, D.H. Wall, R.A. Virginia. 2018. Soil biological responses to C, N and P fertilization in a polar desert of Antarctica. Soil Biology & Biochemistry 122: 7-18. doi: 10.1016/j.soilbio.2018.03.025