Initial response of evapotranspiration from tallgrass prairie vegetation to CO₂ at subambient to elevated concentrations
2008
Polley, H.W. | Johnson, H.B. | Fay, P.A. | Sanabria, J.
1. Effects of CO₂ enrichment on leaf transpiration are well-documented, but our understanding of how CO₂ interacts with other variables to regulate evapotranspiration from plant communities is more limited. 2. A series of weighing lysimeters in which tallgrass prairie species had been planted were exposed to a subambient to elevated gradient in CO₂ in a field chamber. Lysimeters with intact monoliths of three soil types were represented along the CO₂ gradient. We used regression analysis to determine how CO₂ effects on evapotranspiration per unit of soil surface area (ETsoil) and per unit of leaf area (ETla) depended on variation in leaf area index (LAI) and diurnal changes in environmental variables during the initial 6 weeks of CO₂ treatment. 3. CO₂ enrichment reduced ETsoil and ETla, and together with air temperature and LAI accounted for most of the variance in daily values of evapotranspiration explained by multiple regression models. The CO₂ effect on ETsoil did not depend on values of other variables, but CO₂ enrichment reduced ETla most at relatively low air temperatures and low LAI for all soils combined. Higher temperatures countered the CO₂ effect by increasing ETla more at elevated than subambient CO₂. Higher LAI countered the CO₂ effect by decreasing ETla more at subambient than elevated concentrations. Plant (LAI) and environmental effects on ETla differed among soils, possibly because plant growth patterns and physiology differed among soils. 4. Our results imply that the CO₂ effect on evapotranspiration per unit of leaf area will vary with seasonal change in temperature and LAI, independent of seasonal shifts in leaf age and physiological activity.
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