Atmospheric nitrogen deposition in world biodiversity hotspots: the need for a greater global perspective in assessing N deposition impacts

Abstract

Increased atmospheric nitrogen (N) deposition is known to reduce plant diversity in natural and semi-natural ecosystems, yet our understanding of these impacts comes almost entirely from studies in northern Europe and North America. Currently, we lack an understanding of the threat of N deposition to biodiversity at the global scale. In particular, rates of N deposition within the newly defined 34 world biodiversity hotspots, to which 50% of the world's floristic diversity is restricted, has not been quantified previously. Using output from global chemistry transport models, here we provide the first estimates of recent (mid-1990s) and future (2050) rates and distributions of N deposition within biodiversity hotspots. Our analysis shows that the average deposition rate across these areas was 50% greater than the global terrestrial average in the mid1990s and could more than double by 2050, with 33 of 34 hotspots receiving greater N deposition in 2050 compared with 1990. By this time, 17 hotspots could have between 10% and 100% of their area receiving greater than 15 kg N ha À1 yr À1 , a rate exceeding critical loads set for many sensitive European ecosystems. Average deposition in four hotspots is predicted to be greater than 20 kg N ha À1 yr À1 . This elevated N deposition within areas of high plant diversity and endemism may exacerbate significantly the global threat of N deposition to world floristic diversity. Overall, we highlight the need for a greater global approach to assessing the impacts of N deposition.

A global comparison of grassland biomass responses to CO 2 and nitrogen enrichment

“…Several of these regions are also biodiversity hotspots (e.g. Indo-Burma, Phoenix et al 2006), and so the threat to biodiversity as the result of grassland biomass gains may be greatest here. Biomass production is also vital for agricultural systems, and plant responses to N and CO 2 fertilization may have important impacts on local, regional and national economies.…”

Macrophysiology for a changing world

“…The broad-scale effects of these changes are likely to be profound and difficult to predict (see Karnosky et al (2003) and Cassar et al (2007) for examples). Nonetheless, it is clear that if the influences of pollution on biodiversity are to be comprehended, then dedicated investigations of stoichiometric variation at broad spatial scales will be required (Sterner & Elser 2002, p. 364;Phoenix et al 2006). Ehrlich (1997) made it clear that ecologists cannot afford to devote their time only to the questions that pique their intellectual curiosity.…”

Forest ecosystem responses to environmental changes: the key regulatory role of biogeochemical cycling

“…Atmospheric N deposition is known to be responsible for reduced plant diversity in natural and seminatural ecosystems (Phoenix et al 2006). Atmospheric N deposition may initially increase N availability, N mineralization, and nitrification and thus, forest growth in the N-limiting areas (Aber et al 1998;Horswill et al 2008).…”