Submitted to: Global Change Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/6/2013
Publication Date: 4/4/2013
Citation: Hussain, M.Z., VanLoocke, A., Markelz, R., Leakey, A., Ort, D.R., Bernacchi, C.J. 2013. Future carbon dioxide concentration decreases canopy evapotranspiration and soil water depletion by field-grown maize. Global Change Biology. 19(5):1572-1584. Interpretive Summary: Corn and soybean form the largest continuous cropping system in the Midwestern region of United States. Any atmospheric influence on this cropping system will have significant impact on the rainfall pattern of this region. Corn alone comprises more than half of the land area and therefore a critical component of this ecosystem. As a crop with highly efficient photosynthesis, corn photosynthesis is already saturated at present [CO2] concentration. The closing of leaf pores for water exchange, and subsequent reduction in water movement from corn will be the most likely responses, when CO2 concentration in the atmosphere rises. The objective of the study was to quantify the corn responses at elevated [CO2] concentration. Corn was grown for three years at ambient and elevated [CO2] (targeted for 2050) using Free-Air Concentration Enrichment (FACE) technology at the SoyFACE facility in Urbana, Illinois. The water exchange of corn was determined using energy balance approach based on the measurements of energy fluxes that flow in and out of the ecosystem. When corn grown in elevated [CO2], water loss from corn was reduced by 8-11 % along with lesser soil moisture depletion, while heat transfer from plants to the atmosphere increased by 8-15 % along with higher canopy temperature (0.2-0.3 °C). Such corn responses to elevated [CO2] was similar, but smaller than that previously observed for soybean at the same site. However, as predicted by regional scale computer modeling, reduced water loss from corn would results in lower growing season rainfall amounts in the Midwestern US.
Technical Abstract: Together maize and soybean form the largest continuous ecosystem in temperate North America. Thus, any influence of atmospheric changes on maize is likely to have an impact on the region’s hydrological cycle. As a C4 crop, photosynthesis in maize is under most circumstances already CO2-saturated at current [CO2] concentrations and the primary response of maize to elevated [CO2] is decreased stomatal conductance (gs). In the absence of stimulated photosynthesis and productivity at elevated [CO2], reduced gs is not offset by greater canopy leaf area and so reduction in evapotranspiration (ET) have the potential to be greater for C4 than for C3 species. The objective of this study was to quantify the impact of elevated [CO2] on ecosystem energy fluxes and water use of maize (Zea mays). Maize was grown under ambient and elevated [CO2] (550 ìmol mol-1 during 2004 and 2006 and ambient + 200 ppm in 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 and soil heat flux and net radiation. When maize was grown in elevated [CO2], ET decreased (8-11 %; p<0.01) along with lesser soil moisture depletion, while sensible heat flux increased (8-15 Wm-2; p<0.01) along with higher canopy temperature (0.2-0.3 °C). The maize response to elevated [CO2] was smaller than that observed for soybean (C3) at the same site, contrary to our expectation. Coupled with similar, but larger, responses of soybean to elevated [CO2], the decrease in ET and subsequent increases in sensible heat flux highlight the critical role of elevated [CO2] in altering future hydrology and climate of the region that is extensively cropped with these species.