title: Global aspects of C/N interactions determining plant-environment interactions.
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.
authors.affiliation: Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK. j.a.raven@dundee.ac.uk
authors.forename: John A
authors.initials: JA
authors.lastname: Raven
authors.forename: Linda L
authors.initials: LL
authors.lastname: Handley
authors.forename: Mitchell
authors.initials: M
authors.lastname: Andrews
mesh_terms: D002244:Carbon / Q000378:metabolism*; D004777:Environment; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D063245:Plant Development; D010944:Plants / Q000378:metabolism*; D014867:Water / Q000502:physiology
chemical_list: D014867:Water; D002244:Carbon; D009584:Nitrogen