title: Responses of foliar delta13C, gas exchange and leaf morphology to reduced hydraulic conductivity in Pinus monticola branches.
abstract: We tested the hypothesis that branch hydraulic conductivity partly controls foliar stable carbon isotope ratio (delta13C) by its influence on stomatal conductance in Pinus monticola Dougl. Notching and phloem-girdling treatments were applied to reduce branch conductivity over the course of a growing season. Notching and phloem girdling reduced leaf-specific conductivity (LSC) by about 30 and 90%, respectively. The 90% reduction in LSC increased foliar delta13C by about 1 per thousand (P < 0.0001, n = 65), whereas the 30% reduction in LSC had no effect on foliar delta13C (P = 0.90, n = 65). Variation in the delta13C of dark respiration was similar to that of whole-tissues when compared among treatments. These isotopic measurements, in addition to instantaneous gas exchange measurements, suggested only minor adjustments in the ratio of intercellular to atmospheric CO2 partial pressures (ci/ca) in response to experimentally reduced hydraulic conductivity. A strong correlation was observed between stomatal conductance (gs) and photosynthetic demand over a tenfold range in gs. Although ci/ca and delta13C appeared to be relatively homeostatic, current-year leaf area varied linearly as a function of branch hydraulic conductivity (r2 = 0.69, P < 0.0001, n = 18). These results suggest that, for Pinus monticola, adjustment of leaf area is a more important response to reduced branch conductivity than adjustment of ci/ca.
authors.affiliation: Department of Forest Resources, University of Idaho, Moscow, ID 83844-1133, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Cernusak
authors.forename: J D
authors.initials: JD
authors.lastname: Marshall
mesh_terms: D002247:Carbon Isotopes / Q000378:metabolism; D010788:Photosynthesis / Q000502:physiology; D028223:Pinus / Q000033:anatomy & histology / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000502:physiology*; D018547:Plant Stems / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology; D014197:Trees / Q000033:anatomy & histology / Q000502:physiology*; D014867:Water / Q000502:physiology
chemical_list: D002247:Carbon Isotopes; D014867:Water