title: Elevated CO2 effects on canopy and soil water flux parameters measured using a large chamber in crops grown with free-air CO2 enrichment.
abstract: An arable crop rotation (winter barley-sugar beet-winter wheat) was exposed to elevated atmospheric CO(2) concentrations ([CO(2) ]) using a FACE facility (Free-Air CO(2) Enrichment) during two rotation periods. The atmospheric [CO(2) ] of the treatment plots was elevated to 550 ppm during daylight hours (T>5°C). Canopy transpiration (E(C) ) and conductance (G(C) ) were measured at selected intervals (>10% of total growing season) using a dynamic CO(2) /H(2) O chamber measuring system. Plant available soil water content (gravimetry and TDR probes) and canopy microclimate conditions were recorded in parallel. Averaged across both growing seasons, elevated [CO(2) ] reduced E(C) by 9%, 18% and 12%, and G(C) by 9%, 17% and 12% in barley, sugar beet and wheat, respectively. Both global radiation (Rg) and vapour pressure deficit (VPD) were the main driving forces of E(C) , whereas G(C) was mostly related to Rg. The responses of E(C) and especially G(C) to [CO(2) ] enrichment were insensitive to weather conditions and leaf area index. However, differences in LAI between plots counteracted the [CO(2) ] impact on E(C) and thus, at least in part, explained the variability of seasonal [CO(2) ] responses between crops and years. As a consequence of lower transpirational canopy water loss, [CO(2) ] enrichment increased plant available soil water content in the course of the season by ca. 15 mm. This was true for all crops and years. Lower transpirational cooling due to a [CO(2) ]-induced reduction of E(C) increased canopy surface and air temperature by up to 2 °C and 0.5 °C, respectively. This is the first study to address effects of FACE on both water fluxes at canopy scale and water status of a European crop rotation.
authors.affiliation: Institute of Agricultural Climate Research, Johann-Heinrich-von-Thünen Institute (vTI), Braunschweig, Germany. stefan.burkart@vti.bund.de
authors.forename: S
authors.initials: S
authors.lastname: Burkart
authors.forename: R
authors.initials: R
authors.lastname: Manderscheid
authors.forename: K-P
authors.initials: KP
authors.lastname: Wittich
authors.forename: F J
authors.initials: FJ
authors.lastname: Löpmeier
authors.forename: H-J
authors.initials: HJ
authors.lastname: Weigel
mesh_terms: D027461:Beta vulgaris / Q000187:drug effects / Q000502:physiology; D002245:Carbon Dioxide / Q000032:analysis / Q000494:pharmacology* / Q000502:physiology; D018556:Crops, Agricultural / Q000187:drug effects / Q000502:physiology*; D005858:Germany; D001467:Hordeum / Q000187:drug effects / Q000502:physiology; D008834:Microclimate; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects* / Q000502:physiology; D025341:Principal Component Analysis; D012987:Soil / Q000032:analysis*; D014908:Triticum / Q000187:drug effects / Q000502:physiology; D014867:Water / Q000378:metabolism*
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide