title: Stem photosynthesis in a desert ephemeral, Eriogonum inflatum : Characterization of leaf and stem CO2fixation and H2O vapor exchange under controlled conditions.
abstract: The gas exchange characteristics of photosynthetic tissues of leaves and stems of Eriogonum inflatum are described. Inflated stems were found to contain extraordinarily high internal CO2concentrations (to 14000 μbar), but fixation of this internal CO2was 6-10 times slower than fixation of atmospheric CO2by these stems. Although the pool of CO2is a trivial source of CO2for stem photosynthesis, it may result in higher water-use efficiency of stem tissues. Leaf and stem photosynthetic activities were compared by means of CO2fixation in CO2response curves, light and temperature response curves in IRGA systems, and by means of O2exchange at CO2saturation in a leaf disc O2electrode system. On an area basis leaves contain about twice the chlorophyll and nitrogen as stems, and are capable of up to 4-times the absolute CO2and O2exchange rates. However, the stem shape is such that lighting of the shaded side leads to a substantial increase in overall stem photosynthesis on a projected area basis, to about half the leaf rate in air. Stem conductance is lower than leaf conductance under most conditions and is less sensitive to high temperature or high VPD. Under most conditions, the ratio Ci/Cais lower in stems than in leaves and stems show greater water-use efficiency (higher ratio assimilation/transpiration) as a function of VPD. This potential advantage of stem photosynthesis in a water limited environment may be offset by the higher VPD conditions in the hotter, drier part of the year when stems are active after leaves have senesced. Stem and leaf photosynthesis were similarly affected by decreasing plant water potential.
authors.affiliation: Biological Sciences Center, Desert Research Institute, P.O. Box 60220, 89506, Reno, NV, USA.
authors.forename: C B
authors.initials: CB
authors.lastname: Osmond
authors.affiliation: Biological Sciences Center, Desert Research Institute, P.O. Box 60220, 89506, Reno, NV, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Smith
authors.affiliation: Biological Sciences Center, Desert Research Institute, P.O. Box 60220, 89506, Reno, NV, USA.
authors.forename: B
authors.initials: B
authors.lastname: Gui-Ying
authors.affiliation: Biological Sciences Center, Desert Research Institute, P.O. Box 60220, 89506, Reno, NV, USA.
authors.forename: T D
authors.initials: TD
authors.lastname: Sharkey
keywords: Eriogonum inflatum; Internal CO2 concentration; Stem photosynthesis; Water stress; Water-use efficiency