Biodiversity bounces back
Air pollution is a human health issue that also impacts negatively on natural ecosystems. In excessive quantities, forms of nitrogen (N) released into the atmosphere from the burning of fossil fuels and from agriculture are a pollutant. Rothamsted Research scientists, who receive strategic funding from the BBSRC and Lawes Agricultural Trust, in collaboration with other researchers in the UK and Germany, examined whether decreased N emissions to the atmosphere in recent years have affected plant biodiversity on the Park Grass Experiment at Rothamsted in southern England. The researchers analysed a large number of samples and datasets collected from Park Grass, including ECN precipitation chemistry data. The Park Grass experment started in 1856 and is the longest running ecological experiment in the world.
The researchers found that plant biodiversity in grassland communities recovered following a decrease in N emissions to the atmosphere and when fertilizer N was withheld. The findings of the study are published in the journal Nature.
Nitrogen is required for plant growth in agricultural systems and acts as a fertilizer. Both reduced and oxidized forms of N are released into the atmosphere by the burning of fossil fuel. Deposition of atmospheric N in such forms and excessive use of N fertilizer can have negative effects on plant species biodiversity, as it encourages taller species that shade out smaller, less competitive plants. This effect has been observed in UK grasslands where plant species diversity has declined steadily since the 1960s. However, since the 1990s, the introduction of new technologies to reduce N emissions from a variety of sources, including the use of catalytic convertors, has helped decrease N deposition in some areas.
Dr Jonathan Storkey, who led the work at Rothamsted Research, said: “It is really important to address effects on biodiversity by monitoring long-term community dynamics on permanent plots of grassland. We analysed both the number of plant species and how much of each species was present in the sub-plots on Park Grass between 1903 and 2012”.
Plots that received no N fertilizer since the experiment began, were examined. The data revealed a dramatic decline in plant diversity on the experiment between the 1940s and 1990s in line with increasing air pollution. However, the amount of N deposited on the site has declined by approximately 70% since the peak in the late 1980s. In recent years, there has been a consistent increase in the number of species recorded on these plots and a decline in the proportion of competitive grasses. Of particular note was the increase in species belonging to the clover family that are especially sensitive to N. These findings indicate that plant diversity has already responded positively to the decline in N deposition.
The ability of grasslands to recover from N pollution was also confirmed using data from plots that received N fertilizer from 1856 until 1989, when it was stopped. Since then, diversity has increased on some of these plots to levels equivalent to those that had never received any fertilizer.
Rothamsted Research is home to the oldest continuous agricultural field experiments in the world, including the Broadbalk Wheat Experiment, Hoosfield Barley and Park Grass. it is partly because of these long-term studies that the site was chosen as an ECN site.
[Text adapted from Rothamsted Research news article]