Researchers have warned that rising nitrogen emissions from developing nations will soon threaten plant life in some of the most biodiverse parts of the planet.
A team led by Gareth Phoenix of the University of Sheffield has shown that, in the mid-1990s, the average amount of nitrogen deposited on the planet's 34 biodiversity 'hotspots' was more than 50 per cent higher than the global average.
They say this figure could more than double by 2050, at which time nitrogen levels in 17 of the 34 hotspots will exceed critical levels that European nations have set to protect their sensitive ecosystems.
As a result, many of the hotspots will soon be in danger of being damaged by high levels of nitrogen, say the researchers. They add that this may already be true for some areas.
Nitrogen gas is emitted into the atmosphere by cars and industrial processes. Some of it then returns the planet in rain, which can harm plants by changing the nutrient content of soil.
The researchers point out that rapid population growth and industrialisation means developing countries are becoming major emitters of nitrogen.
Emissions from industrialised nations, on the other hand, are stabilising and nitrogen deposition is even declining in some regions.
This suggests developing countries are responsible for the damage suffered by biodiversity hotspots.
Brazil's Atlantic forest, the temperate forests of south-west China, much of South-East Asia, Sri Lanka and the Western Ghats mountain range in southern India are some of the hotspots facing the greatest increase in nitrogren deposition.
Phoenix's team urges more research on nitrogen deposition in developing countries, pointing out that data from Africa and many parts of Asia is scarce.
The Earth's 34 biodiversity hotspots cover two hundredths of its land area, yet are home to half of its plant species. Most are in tropical and subtropical regions of the developing world.
Reference: Global Change Biology 12, 470 (2006)