title: Stem photosynthesis in Psorothamnus spinosus (smoke tree) in the Sonoran desert of California.
abstract: Stem photosynthetic responses to environmental parameters were investigated with Psorothamnus spinosus in the Sonoran Desert of California. Light saturation of stem photosynthesis was equal to maximum midday summer irradance (1600-2000 μmol·m-2·s-1). The optimum temperature for stem photosynthesis was 39°C, and lower stem temperatures (27-35°C) caused significant decreases (up to 50%) in stem photosynthesis. Positive stem photosynthesis was maintained up to 51°C. Stem photosynthesis was relatively insensitive to increasing vpd up to 5 kPa; However, stem conductance decreased by 25% at a vpd of 5 kPa. At vpd greater than 5 kPa stem photosynthesis decreased relatively more than that of stem conductance causing a decrease in water use efficiency and an increase an intercellular carbon dioxide concentration. Maximum stem photosynthetic rates were low (6.2-10.6 μmol·m-2·s-1) on a stem surface area, but, stem photosynthetic rates of young shoots were substantially higher (19.5-33.3 μmol· m-2·s-1) on a projected area basis.
authors.affiliation: Department of Biology, Virginia Polytechnic Institute and State University, 24061, Blacksburg, VA, USA.
authors.forename: Erik T
authors.initials: ET
authors.lastname: Nilsen
authors.affiliation: Hawaiian Sugar Planters' Association, P.O. Box 1057, 96701, Aiea, Hawaii, USA.
authors.forename: F C
authors.initials: FC
authors.lastname: Meinzer
authors.affiliation: Laboratory of Biochemical and Environmental Sciences, University of California at Los Angeles, 900 Veteran Avenue, 90024, Los Angeles, CA, USA.
authors.forename: P W
authors.initials: PW
authors.lastname: Rundel
keywords: Desert; Photosynthesis; Plant stress; Stem