There are some interesting ideas around using nitrogen as a tool to combat climate change, which have attracted attention from scientists and policymakers. However, it seems as though we must be cautious about such potential solutions, due to the complexities of the global nitrogen cycle and its many interactions already touched upon in this blog.
One example of research in this area was summarised nicely in the Scientific American magazine in 2009. The article discusses the experiments of Pregitzer et al. (2008) in forested environments in northern Michigan USA. Pregitzer et al have applied increased concentrations of reactive nitrogen to soils in four different areas of forest (simulating the expected quantity of available nitrogen in 100 years time). They found, expectedly, that tree growth and carbon sequestration increased, but more interestingly rates of decomposition of organic material on the forest floor slowed. This was because the microbial community in the soil had been altered; meaning that lignin (a strong substance in plants that is effective at carbon storage) was less easily broken down by bacteria. The overall result is that nitrogen addition directly alters the ability of the soil to store carbon, and sequestration in forest trees and soils increased considerably. As the soil organic matter is able to store similar quantities of carbon to the forest trees, this is a very significant factor.
Despite these findings, Pregitzer warns that the many negative impacts of excess nitrogen (e.g. acidification, biodiversity loss, smog etc.) outweigh this positive….."One thing that would be a mistake would be to give the implication that nitrogen deposition is a good thing..". There are also major problems with forests becoming saturated with nitrogen, resulting in the leaching of nitrogen into drinking water sources and nitrous oxide emissions (a major greenhouse gas) counteracting the forests benefit in mitigating climate change.
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