title: 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).
abstract: Accurate estimates of the δ(13) C value of CO(2)  respired from roots (δ(13) C(R_root) ) and leaves (δ(13) C(R_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 δ(13) C(R_leaf) , δ(13) C(R_root) , and the δ(13) C values and concentrations of glucose and sucrose in leaves and roots in the C(4)  grass Sporobolus wrightii and the C(3)  tree Prosopis velutina in a savanna ecosystem in southeastern Arizona, USA. Night-time variation in δ(13) C(R_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 δ(13) C values of these respiratory substrates. Strong positive correlations between δ(13) C(R_root)  and root glucose δ(13) C values in P. velutina suggest large diel changes in δ(13) C(R_root)  (were up to 3.9‰) influenced by short-term changes in δ(13) C of leaf-derived phloem C. No diel variation in δ(13) C(R_root)  was observed in S. wrightii. Our findings show that short-term changes in δ(13) C(R_leaf)  and δ(13) C(R_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 δ(13) C of respired CO(2)  in these species.
authors.affiliation: Department of Renewable Resources Department of Botany Program in Ecology, University of Wyoming, Laramie, WY 82071, USA. sunwei8868@gmail.com
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Víctor
authors.initials: V
authors.lastname: Resco
authors.forename: David G
authors.initials: DG
authors.lastname: Williams
mesh_terms: D001130:Arizona; D002245:Carbon Dioxide / Q000032:analysis* / Q000737:chemistry; D002247:Carbon Isotopes / Q000032:analysis / Q000737:chemistry; D019069:Cell Respiration; D017753:Ecosystem; D005947:Glucose / Q000032:analysis; D052585:Phloem / Q000737:chemistry; D017440:Photoperiod; D018515:Plant Leaves / Q000737:chemistry*; D018517:Plant Roots / Q000737:chemistry*; D006109:Poaceae / Q000502:physiology*; D029862:Prosopis / Q000502:physiology*; D012621:Seasons; D013395:Sucrose / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D013395:Sucrose; D005947:Glucose