The Link between Nitrogen Availability and Sequestration of Carbon

As mentioned in my last post, I’m going to look in more detail at the link between the increase in nitrogen deposition and the uptake of carbon from the atmosphere. This blog looks at a few recent papers on the topic.  The atmospheric deposition of nitrogen is thought to enhance the uptake of carbon dioxide from the atmosphere by terrestrial vegetation (Reay et al., 2008), and therefore may help reduce the warming effect produced by greenhouse gas emission.  This is an interesting and potentially beneficial impact of anthropogenic influences on the nitrogen cycle. 

In support of this idea, evidence has been highlighted by Thomas et al. (2010) who have used forest inventory data to examine the impact of nitrogen deposition on tree growth, survival and carbon storage across the north-eastern and north-central USA during the 1980s and 1990s. When their results are extrapolated to cover the entire globe, they estimate that nitrogen deposition could increase tree carbon storage by 0.31 Pg carbon/yr.  

Norby et al. (2010) have investigated the negative feedback on anthropogenic CO₂ present in the atmosphere due to increased CO₂ concentration stimulating plant production.  This feedback is included in models of CO₂ concentration, but not with great certainty as the impact of available nitrogen is anticipated to be a limiting factor for plant productivity.   The experiments of Norby et al. show that increases in net primary productivity under conditions where CO₂ concentrations were elevated drop off over an 11yr timescale.  Their nitrogen budget analysis supports the premise that nitrogen availability was limiting to tree growth and declining over time, and therefore global CO₂ and climate models that assume the CO₂ fertilization effect to be sustained are not supported by this evidence.  Norby et al. say that N limitation and N feedback effects should be incorporated into ecosystem and global models used in climate change assessments.