title: Diurnal and seasonal variation in the carbon isotope composition of leaf dark-respired CO(2) in velvet mesquite (Prosopis velutina).
abstract: We evaluated diurnal and seasonal patterns of carbon isotope composition of leaf dark-respired CO(2) (delta(13)C(l)) in the C(3) perennial shrub velvet mesquite (Prosopis velutina) across flood plain and upland savanna ecosystems in the south-western USA. delta(13)C(l) of darkened leaves increased to maximum values late during daytime periods and declined gradually over night-time periods to minimum values at pre-dawn. The magnitude of the diurnal shift in delta(13)C(l) was strongly influenced by seasonal and habitat-related differences in soil water availability and leaf surface vapour pressure deficit. delta(13)C(l) and the cumulative flux-weighted delta(13)C value of photosynthates were positively correlated, suggesting that progressive (13)C enrichment of the CO(2) evolved by darkened leaves during the daytime mainly resulted from short-term changes in photosynthetic (13)C discrimination and associated shifts in the delta(13)C signature of primary respiratory substrates. The (13)C enrichment of dark-respired CO(2) relative to photosynthates across habitats and seasons was 4 to 6 per thousand at the end of the daytime period (1800 h), but progressively declined to 0 per thousand by pre-dawn (0300 h). The origin of night-time and daytime variations in delta(13)C(l) is discussed in terms of the carbon source(s) feeding respiration and the drought-induced changes in carbon metabolism.
authors: Department of Renewable Resources, University of Wyoming, Laramie, WY 82071, USA. wsun@uwyo.edu
authors: Wei
authors: W
authors: Sun
authors: Víctor
authors: V
authors: Resco
authors: David G
authors: DG
authors: Williams
mesh_terms: D002241:Carbohydrates / Q000032:analysis; D002244:Carbon / Q000737:chemistry*; D002245:Carbon Dioxide / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry; D003624:Darkness; D055864:Droughts; D010788:Photosynthesis; D018515:Plant Leaves / Q000737:chemistry*; D029862:Prosopis / Q000737:chemistry*; D012621:Seasons; D012987:Soil; D013213:Starch / Q000032:analysis; D014867:Water
chemical_list: D002241:Carbohydrates; D002247:Carbon Isotopes; D012987:Soil; D014867:Water; D002245:Carbon Dioxide; D002244:Carbon; D013213:Starch