Long term study shows grasslands can recover naturally from too much atmospheric nitrogen

December 3, 2015 by Bob Yirka report
Park Grass aerial view May 2005. Credit: The Park Grass experiment

(Phys.org)—A long term study conducted by managers of The Park Grass experiment at Rothamsted Research in Harpenden, UK, shows, according to a team of researchers from Germany and the U.K., that under certain conditions, grasslands are able to recover naturally from overexposure to atmospheric nitrogen. In their paper published in the journal Nature, the team describes the condition of grasses and soil at the research center over the course of the past century and a half and what has been learned from it. David Tilman and Forest Isbell with the University of Minnesota offer a News & Views piece on the work done by the team and compare it with findings in other parts of the world.

Scientists know that an overabundance of can lead to loss of plant diversity—Tilman and Isbell explain that the reason this happens is because of the trade-offs involved in the evolutionary process. When plants in a certain area are suddenly faced with a new nutrient, those with adaptations well suited to the new nutrient are able to take full advantage, while those that are not get pushed out. Over the past couple of hundred years, levels of atmospheric nitrogen increased as part of human caused air pollution, but as problems became evident, people in some parts of the world took action to cause less to be emitted which meant less was put into the air. One of those places was Great Britain, a country heavily involved in the industrial revolution and which also took action to reduce such emissions.

During part of this time period a group of progressive thinkers set up a plot of land at Rothamsted Research and planted sections of grasses, with the sections being treated differently—some were fertilized, others were not. This allowed for noting the natural loss of diversification in the grasses that grew on the plots as atmospheric nitrogen levels increased and then as diversification returned, (somewhat) naturally as levels of atmospheric nitrogen were reduced. It was this change that the researchers with this new effort noted and they claim that it shows that under certain circumstances can heal themselves.

There is one major caveat however, the grass blocks at the research center were mowed periodically and the cut removed, which presumably took with it some of the nitrogen.

Explore further: Team studies diversity among nitrogen-fixing plants

More information: J. Storkey et al. Grassland biodiversity bounces back from long-term nitrogen addition, Nature (2015). DOI: 10.1038/nature16444

Abstract
The negative effect of increasing atmospheric nitrogen (N) pollution on grassland biodiversity is now incontrovertible1, 2, 3. However, the recent introduction of cleaner technologies in the UK has led to reductions in the emissions of nitrogen oxides, with concomitant decreases in N deposition4. The degree to which grassland biodiversity can be expected to 'bounce back' in response to these improvements in air quality is uncertain, with a suggestion that long-term chronic N addition may lead to an alternative low biodiversity state5. Here we present evidence from the 160-year-old Park Grass Experiment at Rothamsted Research, UK6, that shows a positive response of biodiversity to reducing N addition from either atmospheric pollution or fertilizers. The proportion of legumes, species richness and diversity increased across the experiment between 1991 and 2012 as both wet and dry N deposition declined. Plots that stopped receiving inorganic N fertilizer in 1989 recovered much of the diversity that had been lost, especially if limed. There was no evidence that chronic N addition has resulted in an alternative low biodiversity state on the Park Grass plots, except where there has been extreme acidification, although it is likely that the recovery of plant communities has been facilitated by the twice-yearly mowing and removal of biomass. This may also explain why a comparable response of plant communities to reduced N inputs has yet to be observed in the wider landscape.

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barakn
not rated yet Dec 03, 2015
This article does not appear to recognize that a reference to atmospheric nitrogen is a reference to elemental nitrogen, a virtually inert substance which makes up an almost invariant 78% of our atmosphere. If they meant to refer to various oxides of nitrogen or ammonia, they should have said so.

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