Arctic soils emit a greenhouse gas called nitrous oxide.  Nitrous oxide is 300 times more powerful than carbon dioxide in warming the planet.  In addition to its potential to warm the planet, nitrous oxide is one way that Arctic soils lose nitrogen.  This is important because nitrogen limits plant growth in the Arctic. Thus, the less nitrogen there is, fewer plants grow and then fewer caribou, muskox, rabbits, etc can live in the Arctic.

The release of nitrous oxide from soil typically increases as the soil temperature increases.  As the Arctic grows warmer, it will begin to contribute to greenhouse gas production.  This is one example of a positive feedback loop. Ecosystems that currently help control our temperature will begin to help increase our global temperature creating a runaway train that may destroy our civilization.  In addition, as these ecosystems grow warmer, they will begin to lose more and more nitrogen to the atmosphere and we do not know if they will then also increase their nitrogen fixation ability.  So, Arctic scientists are very interested in how Arctic soils will respond to temperature increases.

We’ve been investigating this issue at a place called Truelove Lowland which is a beautiful spot on Devon Island in Canada’s Arctic

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Stream on Truelove Lowland

.  We found that, yes, as soils warm, they do indeed emit more nitrous oxide.  However, surprisingly we found that this increase in emission dependended on the form of nitrogen available in the soil.  There are two major forms of inorganic nitrogen in soil, nitrate and ammonia.  Typically, nitrate is the form that is readily available to animals, plants and bacteria.  But in the Arctic, this is not always the case and normally when we do our analyses, we find that the amount of ammonia is the best predictor of how much nitrous oxide the soil is going produce.  In this experiment, when we fertilized with nitrate we saw large increases in nitrous oxide production with increasing temperature but when we fertilized with ammonia, we didn’t see this large increase.   This surprised us because in the field, we knew that the primary source of nitrous oxide was ammonia and not nitrate.  Using chemicals that inhibit certain groups of organisms, here is what we think is going on:

In the Arctic soil, fungi compete so strongly for nitrate that the only form of nitrogen available for release as nitrous oxide is ammonia.   So, this explains our field results, that is, ammonia dominates in the field settings because fungi suck up all the nitrate.

However, in some parts of the Arctic, in the bits that are soggy and wet, a group of organisms called denitrifiers will rapidly respond to climate change, if they have nitrate. They normally can’t get nitrate so this isn’t a problem, unless…

Many other Arctic scientists have found that nitrate levels can rapidly increase if snow depth increases.  It sounds counter-intuitive, but if the Arctic warms, then snow depth will likely increase.  So, people have been investigating what happens when snow depth increases as well as when the ecosystem warms.  Our results, suggest that Arctic soils that are currently unresponsive to increases in temperature, will suddenly become very responsive.

Is this a problem?  We don’t know yet.  How important is nitrous oxide contribution from Arctic soils to the world’s nitrous oxide budget?  Not really that important.  What will happen to nitrogen levels in these soils as they warm?  No one really knows.  We care about this because 50% of Canada’s carbon is safely stored in the Arctic soils.  If climate change was to suddenly release this carbon, very, very bad things would happen to our planet.