In a global first, US researchers have examined ecosystem-specific vulnerabilities to atmospheric nitrogen deposition on a continental scale. A coalition of universities and public bodies studied 15,136 forest, woodland, shrubland and grassland sites across the U.S., measuring the threshold that nitrogen inputs become harmful to plants while accounting for other environmental factors, including climate conditions.
The study found that 24% of the sites surveyed were at or above levels that lead to plant species losses. While that percentage may not appear particularly large it is important to remember that diversity in plant species is essential to ecosystem health. Grasslands, shrublands and woodlands were susceptible to species losses at lower levels of nitrogen deposition than forests and species growing in soils that were more acidic were also more at risk from higher nitrogen deposition.
In Australia, due to poor soil quality fertilisers are needed to support food and fibre production and while it is long known that excessive reactive nitrogen use at the local level has negative impacts; the findings in this paper show that excessive nitrogen deposition levels have a detrimental impact on plant species at the continental level. Considering Australia’s harsh climate and unique biodiversity, a similar study in Australia would be useful to see if the results are replicated.
The take away from the study is that when considering air quality standards, reactive nitrogen levels should be considered as opposed to the focus on nitrogen dioxide levels. Even more ambitiously, the regulation of the use of reactive nitrogen to limit its emissions could be considered.
Paper citation: Simkin et al (2016), Conditional vulnerability of plant diversity to atmospheric nitrogen deposition across the United States, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1515241113
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