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TEAR up the textbooks. Send the soil scientists back to school. Our
understanding of how the world鈥檚 plants absorb and release nitrogen turns out to
be completely wrong. Instead of measuring the workings of undisturbed
ecosystems, a hundred years鈥� worth of botany studies have been recording the
effects of man-made pollution.

For over a century, researchers thought they had the nitrogen cycle licked.
They measured how plants absorbed and released inorganic nitrogen into soils and
streams, and used this information to build models of how life on Earth works.
The dogma was that plants grow by naturally absorbing inorganic nitrogen. 鈥淣ow
this is brought into doubt,鈥� says Nico van Breemen, a soil scientist at
Wageningen Agricultural University in the Netherlands.

A rare study of more than 100 streams in pristine ecosystems in South America
has revealed that, away from pollution, more than 90 per cent of the nitrogen
loss from forests is organic. This suggests that plants in pristine environments
also take up much of their nitrogen in organic form鈥攁n idea that is backed
by some other tentative studies.

Steven Perakis and Lars Hedin of Cornell University in Ithaca, New York, say
their findings are remarkably consistent across all types of forests and
ecosystems. They believe that the picture in the northern hemisphere has been
corrupted by the huge amounts of man-made inorganic nitrogen poured into the
environment from vehicle pollution and artificial fertilisers.

The results are not just an embarrassment in the arcane worlds of ecology and
soil science. Perakis thinks they could fundamentally change our understanding
of the impact of acid rain on forests, and of the likely effects of the build-up
of carbon dioxide in the air and global warming.