335-2 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 (Ψw), 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 (θs) 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 Ψw were measured with a pressure chamber from 044-084 DAP and ranged from -0.3 to -4.0 MPA. The most negative Ψw 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 Ψw, 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).