title: Canopy photosynthesis and transpiration in microgravity: gas exchange measurements aboard Mir.
abstract: The SVET Greenhouse on-board the Orbital Station Mir was used to measure canopy photosynthesis and transpiration rates for the first time in space. During the Greenhouse IIB experiment on Mir (June-January 1997), carbon and water vapor fluxes from two wheat (cv. Superdwarf) canopies were measured using the US developed Gas Exchange Measurement System (GEMS). Gas analyzers capable of resolving CO2 concentration differences of 5 micromoles mol-1 against a background of 0.9% CO2, are necessary to measure photosynthetic and respiratory rates on Mir. The ability of the GEMS gas analyzers to measure these CO2 concentration differences was determined during extensive ground calibrations. Similarly, the sensitivity of the analyzers to water vapor was sufficient to accurately measure canopy evapotranspiration. Evapotranspiration, which accounted for over 90% of the water added to the root zone, was estimated using gas exchange and used to estimate substrate moisture content. This paper presents canopy photosynthesis and transpiration data during the peak vegetative phase of development in microgravity.
authors.affiliation: Plants, Soils & Biometeorology Dept., Utah State University, Logan 84322-4820, USA.
authors.forename: O
authors.initials: O
authors.lastname: Monje
authors.forename: G E
authors.initials: GE
authors.lastname: Bingham
authors.forename: J G
authors.initials: JG
authors.lastname: Carman
authors.forename: W F
authors.initials: WF
authors.lastname: Campbell
authors.forename: F B
authors.initials: FB
authors.lastname: Salisbury
authors.forename: B K
authors.initials: BK
authors.lastname: Eames
authors.forename: V
authors.initials: V
authors.lastname: Sytchev
authors.forename: M A
authors.initials: MA
authors.lastname: Levinskikh
authors.forename: I
authors.initials: I
authors.lastname: Podolsky
mesh_terms: D000389:Air Conditioning / Q000295:instrumentation; D002245:Carbon Dioxide / Q000378:metabolism; D004780:Environment, Controlled; D004784:Environmental Monitoring; D010788:Photosynthesis / Q000502:physiology*; D018517:Plant Roots / Q000378:metabolism; D018526:Plant Transpiration / Q000502:physiology*; D013026:Space Flight / Q000295:instrumentation*; D014908:Triticum / Q000254:growth & development / Q000378:metabolism*; D014867:Water / Q000378:metabolism; D014893:Weightlessness
chemical_list: D014867:Water; D002245:Carbon Dioxide