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JXB Advance Access published online on November 28, 2003
Journal of Experimental Botany, doi:10.1093/jxb/erh011
© 2003 by Oxford University Press
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Received May 2, 2003; accepted August 11, 2003
© 2003 Society for Experimental Biology

FOCUS PAPER

Global aspects of C/N interactions determining plant-environment interactions

John A Raven 1*, Linda L Handley 2, and Mitchell Andrews 3

1 Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK; Columbia University Biosphere 2 Center, 32540 S. Biosphere Road, PO Box 689, Oracle, AZ 85623, USA
2 Columbia University Biosphere 2 Center, 32540 S. Biosphere Road, PO Box 689, Oracle, AZ 85623, USA; Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
3 School of Sciences, University of Sunderland, Sunderland SR1 3SD, UK

* To whom correspondence should be addressed. E-mail: j.a.raven{at}dundee.ac.uk.


  Abstract

The atomic C:N ratio in photolithotrophs is a function of their content of nucleic acids, proteins, lipids, polysaccharides, and other organic materials, and varies from about 5 in some protein-rich microalgae to much higher values in macroalgae and in higher plants with relatively more structural and energy storage materials. These differences in C:N ratios among organisms means that there is more N assimilation by photosynthetic organisms in the oceans than on land despite the near equality of global photosynthetic C assimilation rates in the two environments. Aquatic organisms obtain inorganic C and inorganic N from the surrounding water. Terrestrial photolithotrophs obtain inorganic C, dinitrogen (by diazotrophy) and some combined N from the atmosphere, with the remaining combined N coming from the soil. The nitrogen cost of growth (biomass production rate per unit plant N) varies with the C:N ratio and specific growth rate of the organism. The C:N ratio of plants can be increased with no, or minimal, decrease in growth rate by switching from N-containing to N-free solutes involved in, for example, UV-B screening or by reducing the content of particular proteins. The water cost of growth (water lost per unit biomass gain) in terrestrial plants is a function of N supply and of C supply; water cost is lower with higher N and C availability. Water supply is also important in determining denitrification rates on land and on N (and C) fluxes from terrestrial to aquatic systems.

Key words: Agriculture, algae, astrochemistry, carbon, chemical defence, compatible solutes, ecology, evolution, free radical scavenging, nitrogen, UV-B screening.


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