Environmental and physiological controls on the carbon isotope composition of CO2 respired by leaves and roots of a C3 woody legume (Prosopis velutina) and a C4 perennial grass (Sporobolus wrightii)

Authors

  • WEI SUN,

    Corresponding author
    1. Department of Renewable Resources
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    • Present address: Institute of Grassland Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Changchun, Jilin 130024, China.

  • VÍCTOR RESCO,

    1. Department of Renewable Resources
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    • Present address: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, NSW 2753, Australia.

  • DAVID G. WILLIAMS

    1. Department of Renewable Resources
    2. Department of Botany
    3. Program in Ecology, University of Wyoming, Laramie, WY 82071, USA
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W. Sun. Fax: +86 431 8569 5065; e-mail: sunwei8868@gmail.com; sunwei@nenu.edu.cn

ABSTRACT

Accurate estimates of the δ13C value of CO2 respired from roots (δ13CR_root) and leaves (δ13CR_leaf) are important for tracing and understanding changes in C fluxes at the ecosystem scale. Yet the mechanisms underlying temporal variation in these isotopic signals are not fully resolved. We measured δ13CR_leaf, δ13CR_root, and the δ13C values and concentrations of glucose and sucrose in leaves and roots in the C4 grass Sporobolus wrightii and the C3 tree Prosopis velutina in a savanna ecosystem in southeastern Arizona, USA. Night-time variation in δ13CR_leaf of up to 4.6 ± 0.6‰ in S. wrightii and 3.0 ± 0.6‰ in P. velutina were correlated with shifts in leaf sucrose concentration, but not with changes in δ13C values of these respiratory substrates. Strong positive correlations between δ13CR_root and root glucose δ13C values in P. velutina suggest large diel changes in δ13CR_root (were up to 3.9‰) influenced by short-term changes in δ13C of leaf-derived phloem C. No diel variation in δ13CR_root was observed in S. wrightii. Our findings show that short-term changes in δ13CR_leaf and δ13CR_root were both related to substrate isotope composition and concentration. Changes in substrate limitation or demand for biosynthesis may largely control short-term variation in the δ13C of respired CO2 in these species.

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