Elevated CO2 and leaf longevity in the C-4 grassland-dominant Andropogon gerardii

In central U.S. grasslands, plant and ecosystem responses to elevated CO2 a re most pronounced when water availability is limited. In a northeast Kansa s grassland, responses to elevated CO2 in leaf area, number, development, a nd longevity were quantified for the tallgrass prairie dominant, Andropogon gerardii. Plants were grown in open-top chambers (OTCs) modified to limit water availability and to maximize responses to elevated CO2. In OTCs with elevated ( x 2 ambient) levels of CO2, aboveground biomass production and l eaf water potentials were increased significantly compared with those of pl ants in OTCs with ambient CO2. There were no differences in leaf area or le af number per tiller in A. gerardii in elevated compared with ambient OTCs. However, leaf area in adjacent unchambered plots with greater water availa bility was significantly higher than in the OTCs. The time required for dev eloping leaves to achieve maximum leaf area was reduced by 29%, and the per iod of time until leaves senesced was increased by 20% for plants exposed t o elevated compared with ambient CO2. Thus, leaves of this C-4 grass specie s expanded more rapidly (6 d) and remained green longer (9 d) when exposed to elevated CO2. Such CO2-mediated increases in leaf longevity in the domin ant species may allow this grassland to respond more opportunistically to t emporally variable rainfall patterns in high-CO2 environments. These respon ses should be included in leaf-based simulation models that attempt to mech anistically link physiological alterations to predicted canopy responses to increased CO2.