title: Reconstructing the δ(18) O of atmospheric water vapour via the CAM epiphyte Tillandsia usneoides: seasonal controls on δ(18) O in the field and large-scale reconstruction of δ(18) Oa.
abstract: Using both oxygen isotope ratios of leaf water (δ(18) OL ) and cellulose (δ(18) OC ) of Tillandsia usneoides in situ, this paper examined how short- and long-term responses to environmental variation and model parameterization affected the reconstruction of the atmospheric water vapour (δ(18) Oa ). During sample-intensive field campaigns, predictions of δ(18) OL matched observations well using a non-steady-state model, but the model required data-rich parameterization. Predictions from the more easily parameterized maximum enrichment model (δ(18) OL-M ) matched observed δ(18) OL and observed δ(18) Oa when leaf water turnover was less than 3.5 d. Using the δ(18) OL-M model and weekly samples of δ(18) OL across two growing seasons in Florida, USA, reconstructed δ(18) Oa was -12.6 ± 0.3‰. This is compared with δ(18) Oa of -12.4 ± 0.2‰ resolved from the growing-season-weighted δ(18) OC . Both of these values were similar to δ(18) Oa in equilibrium with precipitation, -12.9‰. δ(18) Oa was also reconstructed through a large-scale transect with δ(18) OL and the growing-season-integrated δ(18) OC across the southeastern United States. There was considerable large-scale variation, but there was regional, weather-induced coherence in δ(18) Oa when using δ(18) OL . The reconstruction of δ(18) Oa with δ(18) OC generally supported the assumption of δ(18) Oa being in equilibrium with precipitation δ(18) O (δ(18) Oppt ), but the pool of δ(18) Oppt with which δ(18) Oa was in equilibrium - growing season versus annual δ(18) Oppt - changed with latitude.
authors.affiliation: Department of Biology, University of Pennsylvania, 433 S. University Ave, Philadelphia, PA, 19104, USA.
authors.forename: Brent R
authors.initials: BR
authors.lastname: Helliker
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D005431:Florida; D016014:Linear Models; D008685:Meteorological Concepts; D008954:Models, Biological; D010103:Oxygen Isotopes; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D012621:Seasons; D013227:Steam; D013696:Temperature; D031232:Tillandsia / Q000254:growth & development / Q000378:metabolism*; D014768:Virginia
chemical_list: D010103:Oxygen Isotopes; D013227:Steam; D002245:Carbon Dioxide; D002244:Carbon
keywords: Crassulacean acid metabolism; hydrological cycle; leaf water enrichment; oxygen isotope.