Print PageThe global nitrogen (N) cycle has been transformed by human activities. With continued growth of the world population and increasing demand for food, pressures on the global nitrogen cycle are set to increase. N deposition has the potential to impact on semi-natural plant communities in a number of different ways resulting in changes in tissue nutrient stoichiometry and metabolism, changes in species composition and changes in species richness. This talk will draw on the results of several large-scale studies in Europe investigating the impact of N deposition on semi-natural vegetation: a European survey of 153 acid grasslands examining both spatial and temporal changes in biogeochemistry and species composition and diversity; a large scale survey of habitat change in the UK; and an investigation of individual species responses using national vegetation records for the UK from four large-scale tetrad and hectad datasets (Vascular Plant Database, Botanical Society of the British Isles Local Change Survey, British Bryological Society Database, and British Lichen Society Database). This project used generalised additive models (GAMs) to assess the impact of N deposition on individual species presence, and on summary variables, taking into consideration other potential drivers including climate, land use and sulphur deposition.
Results/Conclusions
The results of these projects clearly show a negative relationship between N deposition and species richness in semi-natural habitats in Europe. These results were apparent in both the European survey of grasslands and the large scale habitat survey which showed declines in heathlands, bogs and other grassland communities. Furthermore, the results highlight the importance of the cumulative effects of N deposition showing declines in species richness over time. Soil chemistry also changed along the deposition gradient showing a reduction in pH and a consequent change in the availability of metals and an increase in the carbon to nitrogen ratio. Although climate and soil variables were important drivers of species composition in acid grassland there were also changes in species composition attributable to N deposition. The results show a change towards species tolerant of acid soils.
All of the habitats examined using national vegetation records showed signs of nutrient enrichment related to nitrogen deposition. A number of vascular plant, bryophyte and lichen species were identified as showing clear relationships with nitrogen deposition. All habitats contained species that showed declines in their probability of presence with increasing N deposition.
