Impacts of atmospheric nitrogen deposition on European calcifuge grasslands

Background/Question/Methods

Atmospheric deposition of reactive nitrogen (N) is a global problem resulting in negative consequences for biodiversity resulting from direct toxicity, increased susceptibility to environmental stresses and soil-mediated effects of acidification and eutrophication.  Experiments have suggested that reactive nitrogen deposition may reduce species richness in plant communities.  However, until recently there was no clear evidence that regional air pollution was actually reducing biodiversity on a regional scale.  An extensive field survey of acidic grasslands along a gradient of atmospheric nitrogen deposition in the UK showed a dramatic decline in plant-species richness with increasing atmospheric nitrogen deposition.  Changes in soil chemistry were also observed.  Combining the results of this gradient study with experimental manipulations allowed us to estimate the timescale of the observed change in species richness. 

This project builds on the results collected in the UK survey to investigate changes in species richness further.  In addition to the 68 calcifuge grasslands already surveyed in the UK, we have surveyed 70 calcifuge grassland sites throughout the Atlantic biogeographic region of Europe.  At each site, data were collected on species composition, soil chemistry and plant-tissue chemistry. 

Results/Conclusions Results/Conclusions

Initial results of the project will be presented, demonstrating declines in species richness and changes in species composition across the Atlantic biogeographic zone of Europe together with changes in soil chemistry.  We also report results from a large British survey showing that similar declines in species richness have been observed in other vegetation communities.

Using plant characteristics and functional traits we examined changes in vegetation species composition along the gradient of N deposition in the UK. Functional traits were used to identify change in response to soil pH together with an index of soil acidity preference developed using regional survey data.

The results suggest that soil acidification as opposed to eutrophication and consequent competition between species is predominantly responsible for shifts in species composition linked to N deposition.  Soil acidification may be leading to reduced nutrient availability preventing the effects of N addition being apparent.