title: Gas exchange and SO2fumigation studies with irrigated and unirrigated field grown Diplacus aurantiacus and Heteromeles arbutifolia.
abstract: Experiments were performed on an evergreen (Heteromeles arbutifolia) and a drought deciduous shrub (Diplacus aurantiacus) to determine, 1) whether approaches for evaluating SO2absorption by leaves in laboratory studies could be extended to field studies, 2) the effects of irrigation on metabolism and SO2responses of the study species during a season when water was limiting, 3) to interpret SO2responses on the basis of SO2flux rates. Laboratory-developed approaches for evaluating SO2absorption by leaves were found to be suitable for use with field plants, despite field plants having lower gas exchange rates. Supplementing water during times of deficit did not override all the biological and environmental factors that limited photosynthesis (A). Irrigation increased leaf longevity of D. aurantiacus, and stomatal conductance to water vapour (g); g was also shown to increase with H. arbutifolia on irrigation. Irrigation profoundly influenced plant response to SO2. Unwatered D. aurantiacus had only a small g and therefore a reduced capacity to absorb SO2and respond to SO2; which resulted in apparent SO2avoidance. Water availability and SO2both affect g and therefore, SO2flux rates into the mesophyll. Different ambient SO2concentrations of 8.3 and 26.2 μmol m-3(0.2 and 0.6 ppm) were both found to result in similar SO2flux rates into the leaf, due to variations in g in response to water availability. Changes in g did not always result in changes in A, implying that carbon fixation may be little affected by some SO2exposures, although still potentially affecting such processes as maintenance of leaf water potential, transpirational cooling and nutrient uptake.
authors.affiliation: Department of Plant Pathology, Physiology and Weed Science, Laboratory for Air Pollution Impact to Agriculture and Forestry, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA.|Department of Biological Sciences, University of Lancaster, LA1 4YQ, Lancaster, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Atkinson
authors.affiliation: Department of Plant Pathology, Physiology and Weed Science, Laboratory for Air Pollution Impact to Agriculture and Forestry, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA.|Department of General Science, Oregon State University, 97331, Corvallis, OR, USA.
authors.forename: W E
authors.initials: WE
authors.lastname: Winner
authors.affiliation: Department of Biological Sciences, Stanford University, 94305, Stanford, CA, USA.
authors.forename: H A
authors.initials: HA
authors.lastname: Mooney
keywords: Diplacus aurantiacus (Curtis) Jeps.; Gas exchange; Heteromeles arbutifolia (Ait.) Roem.; Irrigation; Sulphur dioxide