Nitrogen’s intense impact

1 January 2014 by Liz O'Connell, posted in Water Tracks

The Alaskan Tundra, August 2013. / Image Maisotti (Creative Commons Attribution 3.0 Unported license)

The Alaskan Tundra, August 2013. / Image Maisotti (Creative Commons Attribution 3.0 Unported license)

Laura Nielsen for Frontier Scientists

Nitrogen is one of the most abundant elements on Earth; nitrogen gas (N2) makes up 78% of Earth’s atmosphere. Nitrogen is also an essential element for all organisms. In order to live and grow, plants and animals need the hydrogen (H) and oxygen (O) which compose water, as well as carbon (C), nitrogen (N) and phosphorus (P). Organisms use nitrogen to make proteins, amino acids, and more. Plants use it to create chlorophyll, which they need to perform photosynthesis. However, organisms cannot use nitrogen gas (N2) directly. They need to obtain nitrogen in a different form.

Many nitrogen transformations occur because of bacteria, tiny microorganisms living in soil. The process through which nitrogen moves through the environment, changes forms, becomes utilized by organisms, and once more returns to the air or soil, is called the nitrogen cycle.

Transforming and using nitrogen

Nitrogen-fixing bacteria in soil convert nitrogen gas (N2) into nitrogen compounds during a process called nitrogen fixation. Lightning strikes can do the same, but are much more rare. Nitrogen-fixing bacteria use nitrogen gas (N2) and release Ammonium (NH4).

Meanwhile, dead plants and animals are decomposed by bacteria and fungi. The decomposers release the nitrogen present in the organisms' bodies into the soil as Ammonium (NH4) through a process called ammonification.

Ammonium (NH4) in the soil is turned into Nitrites (NO2) and Nitrates (N03) by nitrifying bacteria during a process called nitrification. These nitrogen compounds, known as fixed forms of nitrogen, are highly useful to plants. Plants assimilate or absorb Nitrites (NO2) and Nitrates (N03) through their roots (assimilation). With these nitrogen compounds, plants build chlorophyll, proteins, and amino acids and nucleic acids.

Most other organisms– including humans– get the nitrogen they need to live by eating plants.

The Nitrogen Cycle / Courtesy Environmental Protection Agency

The Nitrogen Cycle / Courtesy Environmental Protection Agency

Humans and the nitrogen cycle

Humans are affecting the nitrogen cycle by burning fossil fuels, raising livestock that create animal waste, adding nitrogen fertilizers to the environment, and dumping sewage into water. Our actions impact even remote places like the Arctic.

In the Alaskan tundra, soil can remain frozen year-round. This frozen ground, or permafrost, stores layers of ancient organisms: dead plants and even animals that have long avoided decomposition because the temperature is so cold. Things are changing, though. Earth's climate is warming, and the Arctic is warming faster than any other region.

As permafrost thaws, previously frozen organic matter decomposes. Microbes, tiny microorganisms like bacteria, become more active as thaw increases. Where once they had to rely on snow bringing trace amounts of nitrogen to the ecosystem through atmospheric deposition (snow carrying tiny particles from the air to the ground), they can now feed off newly-thawed organisms deeper underground. The increased decay of once-living organisms releases nitrogen into the Arctic ecosystem. More nutrients means more possibilities for growing plants, but has other implications as well.

Nitrogen escaping permafrost

When nitrogen that was previously frozen is released in the Arctic tundra it can be a boon to local organisms which– of course– require nitrogen to live. However, there may be more nitrogen suddenly available than local plants and bacteria can use. Some excess nitrogen is released back into the atmosphere by dentrifying bacteria which perform dentrification to turn nitrogen compounds back into nitrogen gas (N2). Other excess nitrogen moves through the snowmelt-fed ecosystem of the Arctic carried by water, which is one of the reasons why scientists are studying water tracks in the Alaskan Arctic.

A sudden influx of nitrogen in a system that normally has little nitrogen creates problems. Nitrate (NO3) is extremely mobile, moving easily with water through soil. The National Park Service sums it up: "Excess N [nitrogen] can leak out of soils into streams and lakes, where it can cause blooms of algae. In addition, more N [nitrogen] may be lost to the atmosphere as nitrous oxide, a greenhouse gas that influences global warming 300 times more than carbon dioxide, and contributes to ozone depletion in the atmosphere." When too much nitrous oxide is present in the atmosphere it causes acid rain. Thawing permafrost releases not only nitrous oxide (N2O), but also carbon dioxide (CO2) and methane (CH4), all greenhouse gasses which will increase future global warming.

Frontier Scientists: presenting scientific discovery in the Arctic and beyond

References:

  • 'Biological Nitrogen Fixation' Stephen C. Wagner, Nature Education Knowledge Project 3(10):15 (2012)
    http://www.nature.com/scitable/knowledge/library/biological-nitrogen-fixation-23570419
  • 'Nitrogen Cycle' Scott C. Killpack and Daryl Buchholz, University of Missouri Department of Agronomy (1993)
    http://extension.missouri.edu/p/WQ252
  • 'Nitrogen in the Nation's Rain' National Atmospheric Deposition Program (2000)
    nadp.isws.illinois.edu/lib/brochures/nitrogen.pdf
  • 'Permafrost Thaw and the Nitrogen Cycle Fact Sheet' Dave Schirokauer, Denali National Park and Preserve Center for Resources, Science, and Learning (2012) DENA-FS-061-2012 Denali Park, Alaska
    http://www.nps.gov/dena/naturescience/upload/Permafrost_N_2012.pdf

4 Responses to “Nitrogen’s intense impact”

  1. doug Reply | Permalink

    Most animals eat plants as a source of nitrogen huh?

    Apparently there's no nitrogen in protein. And predators don't exist.

    • Jeff Reply | Permalink

      And where did the animal that produced the protein you ate get the nitrogen? It all eventually leads back to plants. Besides, I would have to believe that the vast majority of animals do actually eat plants as a source of nitrogen. Logically there has to be more plant eaters than meat eaters.

      • Kevin Reply | Permalink

        That would be totally logical if predators only ate herbivores, but there are lots of predators that eat other predators. I am not saying that there are more than one than of another, but I am not so sure it has to be that way.

        Of course, animals cannot fix nitrogen, many, if not most, plants don't even fix nitrogen. A lot of it goes all the way back to bacteria, then to plants, then to animals.

        • Joshua Naterman Reply | Permalink

          There are also an enormous amount of animals that eat insects. Insects are in the animal kingdom, and are an enormous source of protein for many birds, mammals, and lizards, especially those lower on the food chain. At the lowest level, with the highest total population, the bottom tier animals and insects eat plants or plant products (nectar, etc). So, if you want to play a pure numbers game, then plant eaters far outnumber non-plant eaters.

          Of course when you get right down to it, since this article (or its illustration of the nitrogen cycle) makes no explicit mention of animals eating animals, or humans eating meats and consuming dairy as a major source of protein in most places... this entire discussion is ridiculous.

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