Retrofit of a Soil-Plant-Atmosphere-Research (SPAR) Experimental Database for Application in Agmips.

Rising levels of atmospheric [CO₂] affect transpiration and absorption processes of wheat (Triticum aestivum L.).  The internal water content of a wheat plant, as indicated by total leaf water potential (Ψ_w), is dependent on both water loss and uptake. Our objective was to determine if the ameliorating effect of elevated CO₂ on alleviating drought was dependent on growth stage (vegetative vs. reproductive). Spring wheat (cv. Yecora Rojo) was hand planted (140 plants m²) on 29 Jan. 1988 in 10 SPAR units at Mississippi State, Mississippi, controlled at a constant day/night temperatures of 23/15 ^oC and vapor pressure deficits of 1.0/0.4  kPa.  Atmospheric [CO₂] was maintained at 340, 450, and 600 ±15 μmol mol^-1.  Volumetric soil-water content (θ_s) was maintained at near saturation (NS), with a soil dehydration cycle initiated at 027 (VS: vegetative) and 044 (RS: reproductive) days after planting (DAP).  ANOVAs were performed using orthogonal contrast for a 3x3 response surface, with the middle treatment (450 μmol mol^-1 and VS) replicated,.  Predawn to sunset Ψ_w were measured with a pressure chamber from 044-084 DAP and ranged from -0.3 to -4.0 MPA.  The most negative Ψ_w occurred for 340 μmol mol^-1 VS treatment, whereas the least negative occurred for 600 μmol mol^-1 NS treatment. Overall, elevated CO₂ caused less negative Ψ_w, but the degree of drought stress alleviation was greater during VS compared with RS. Hence, the ameliorating effect of CO₂ in mitigating drought stress may be coupled with alterations that occur when leaves acclimate to drought during their growth and development. A regression-based analysis of simulations with the CSM-CROPSIM-CERES demonstrated good agreement between observed and predicted biomass (g m^-2).