Global warming and the associated rise in carbon dioxide levels could spell the end for many of Britain's indigenous plants, researchers have revealed.

Although the research relates to wild plants it could provide clues on how best to manage food crops as the climate changes because of the build-up of fossil fuel burning, the main cause of the carbon dioxide.

Preliminary evidence from researchers at the Universities of Essex, Lancaster and Wales reveals that certain types of plants, particularly those which already grow in "stressed" conditions, could suffer if, as projected, carbon dioxide levels double between now and the end of the 21st century.

Because they respond poorly to carbon dioxide-rich environments, shrubs and possibly rare flowers growing in difficult environments, such as salt marshes, could find themselves overrun by other species which thrive on higher carbon dioxide concentrations.

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Now, thanks to a grant from the Natural Environment Research Council, scientists hope to continue their research project to discover the precise mechanisms by which plant photosynthesis is affected by higher carbon dioxide concentrations, how plants divide up food and how they use water under the same conditions.

Steve Long, of the department of biological and chemical sciences at the University of Essex, said that the atmospheric concentration of carbon dioxide had increased from 0.0 per cent in 1800 to 0.035 per cent today. It is predicted that it could double to 0.07 per cent by the end of the next century.

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However, predictions are complex because of the many variables, not least the effect of temperature rises on plants because of increased atmospheric carbon dioxide, which creates a greenhouse effect.

Professor Long said that small-scale research on wild plants was important but he said that it was vital that governments also ploughed more money into large-scale research projects to assess how food crops will be affected by global warming.

The research is part of the Government's Terrestrial Initiative in Global Environment Research (TIGER) and in addition to the Universities of Essex, Lancaster and Wales's work with plants, the University of London is studying insects. The Institute of Fresh Water Ecology and the Institute of Terrestrial Ecology are also involved in research. All received a share of a Pounds 250,000 total grant.