title: Future carbon dioxide concentration decreases canopy evapotranspiration and soil water depletion by field-grown maize.
abstract: Maize, in rotation with soybean, forms the largest continuous ecosystem in temperate North America, therefore changes to the biosphere-atmosphere exchange of water vapor and energy of these crops are likely to have an impact on the Midwestern US climate and hydrological cycle. As a C4 crop, maize photosynthesis is already CO2 -saturated at current CO2 concentrations ([CO2 ]) and the primary response of maize to elevated [CO2 ] is decreased stomatal conductance (gs ). If maize photosynthesis is not stimulated in elevated [CO2 ], then reduced gs is not offset by greater canopy leaf area, which could potentially result in a greater ET reduction relative to that previously reported in soybean, a C3 species. The objective of this study is to quantify the impact of elevated [CO2 ] on canopy energy and water fluxes of maize (Zea mays). Maize was grown under ambient and elevated [CO2 ] (550 μmol mol(-1) during 2004 and 2006 and 585 μmol mol(-1) during 2010) using Free Air Concentration Enrichment (FACE) technology at the SoyFACE facility in Urbana, Illinois. Maize ET was determined using a residual energy balance approach based on measurements of sensible (H) and soil heat fluxes, and net radiation. Relative to control, elevated [CO2 ] decreased maize ET (7-11%; P < 0.01) along with lesser soil moisture depletion, while H increased (25-30 W m(-2) ; P < 0.01) along with higher canopy temperature (0.5-0.6 °C). This reduction in maize ET in elevated [CO2 ] is approximately half that previously reported for soybean. A partitioning analysis showed that transpiration contributed less to total ET for maize compared to soybean, indicating a smaller role of stomata in dictating the ET response to elevated [CO2 ]. Nonetheless, both maize and soybean had significantly decreased ET and increased H, highlighting the critical role of elevated [CO2 ] in altering future hydrology and climate of the region that is extensively cropped with these species.
authors.affiliation: Institute for Genomic Biology, University of Illinois, Urbana, IL 61801, USA.
authors.forename: Mir Zaman
authors.initials: MZ
authors.lastname: Hussain
authors.forename: Andy
authors.initials: A
authors.lastname: Vanloocke
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Siebers
authors.forename: Ursula M
authors.initials: UM
authors.lastname: Ruiz-Vera
authors.forename: R J
authors.initials: RJ
authors.lastname: Cody Markelz
authors.forename: Andrew D B
authors.initials: AD
authors.lastname: Leakey
authors.forename: Donald R
authors.initials: DR
authors.lastname: Ort
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Bernacchi
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002940:Circadian Rhythm; D057231:Climate Change; D004734:Energy Metabolism; D007087:Illinois; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration; D012621:Seasons; D012987:Soil / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000378:metabolism*; D003313:Zea mays / Q000502:physiology*
chemical_list: D012987:Soil; D014867:Water; D002245:Carbon Dioxide