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.

Biomass sorghum and maize have similar water-use-efficiency under non-drought conditions in the rain-fed Midwest U.S.

“…are consistent with reports for rain-fed maize in the Midwest, US (450-612 mm; Hickman et al, 2010;Djaman et al, 2013;Hussain et al, 2013;Zeri et al, 2013;Hamilton et al, 2015). We found similar total ET for maize and biomass sorghum in non-drought conditions, which may reduce concerns over regional hydrologic effects associated with the introduction of biomass sorghum into Midwest crop rotations .…”

“…The residual energy balance (REB) method was selected due to its ability to detect relative differences in ET among plots of limited fetch (Kimball et al, 1994). Numerous previous studies have used the REB method for maize and sorghum agroecosystems (Kimball et al, 1994;Triggs et al, 2004;Hickman et al, 2010;Hussain et al, 2013). Previous studies (Kimball et al, 1994;Triggs et al, 2004;Bernacchi et al, 2007;VanLoocke et al, 2012a) have demonstrated that the REB method is appropriate for plots of relatively small fetch, since the implementation of radiometric temperature in aerodynamic resistance equations reduces fetch requirements compared to other micrometeorological methods (Kimball et al, 1994).…”

Global warming and 21st century drying

“…4; Table 1). Other experiments have found only modest changes (\15 %) in evapotranspiration fluxes and soil water content with enhanced [CO 2 ] (e.g., Hussain et al 2013;e.g., Inauen et al 2013;e.g., Stocker et al 1997). Large uncertainties in the effect of enhanced [CO2] on future hydroclimate projections, namely through the modification of stomatal resistance, make characterizing the impact of this mechanism on a global scale simply too difficult to quantify for our purposes herein.…”

Correlating hydrologic reinforcement of vegetated soil with plant traits during establishment of woody perennials

“…Changes in stomatal opening, and hence leaf conductance to water vapor, can strongly affect root-water uptake and hence the soil water balance (Hungate et al 2002;Gedney et al 2006;Betts et al 2007). Hussain et al (2013) showed that a decrease in leaf conductance of Maize caused a reduction of soil water depletion by 5% -10%. Simple measurements of leaf conductance using a portable porometer could provide a quick assessment of transpiration of a plant.…”