ARS | Publication request: Long-term growth of soybean and maize at elevated [CO2] under free-air concentration enrichment (FACE) reduces soil moisture depletion

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract
Publication Acceptance Date: October 10, 2006
Publication Date: October 10, 2006
Publisher's URL: http:////www.aspb.org/meetings/transpiration06/justabstracts.cfm
Citation: Leakey, A.B., Long, S.P., Ort, D.R. 2006. Long-term growth of soybean and maize at elevated [CO2] under free-air concentration enrichment (FACE) reduces soil moisture depletion [abstract]. American Society of Plant Biologists. Available at http://www.aspb.org/meetings/transpiration06/justabstracts.cfm.

Technical Abstract: Stomatal conductance (gs) is lower when plants are grown at elevated [CO2] compared to ambient [CO2]. This is often assumed to reduce plant water use and ameliorate water stress by conserving soil moisture. However, under field conditions canopy size, canopy structure, microclimate and fluxes of water in the soil column also regulate plant water use. Therefore, lower gs does not guarantee reduced crop water use. This study measured the soil moisture content over two growing seasons below soybean and maize canopies grown at ambient [CO2] (380 micromol mol-1) and elevated [CO2] (550 micromol mol-1) using Free-Air Concentration Enrichment (FACE). Soil moisture was estimated in 10-cm increments between depths of 5-105 cm using a capacitance probe, every 2-5 days. There was a significant decrease in soil moisture depletion below both crops when grown at elevated [CO2]. After large rain events there was little or no difference in soil moisture at ambient and elevated [CO2]. During dry periods soil moisture under elevated [CO2] declined less rapidly than under ambient [CO2]. Consequently, during dry periods, when the plants were most likely to experience stress, there was up to 20 % (v/v) greater soil moisture between depths of 5-55 cm under elevated [CO2]. During the drier year both (1) soil moisture depletion and (2) conservation of soil moisture under elevated [CO2] extended deeper into the soil. These results indicate the temporal and spatial complexity of changes in soil moisture when C3 and C4 plants are grown at elevated [CO2]. This is an important consideration when predicting how elevated [CO2] will impact the frequency and intensity of drought stress in natural and managed plant communities.