Leaf Photosynthesis Water Use of Big Bluestem under Elevated Carbon Dioxide
1991
Kirkham, M. B. | He, H. | Bolger, T. P. | Lawlor, D. J. | Kanemasu, E. T.
With the atmospheric concentration of CO₂ increasing, it is importanto know how this will affect crop growth. The objective of the study was to determine the effect of elevated CO₂ on big bluestem (Andropogon gerardii Vitman) growing in a tallgrass prairie on Tully silty clay loam (fine, mixed, mesic Pachic Argiustoll) kept a high water level (field capacity) or a low water level (half field capacity). Sixteen cylindrical plastic chambers were placed on the prairie to maintain the two levels of CO₂ (mean ± SD: 337 ± 32 and 658 ± 81 µmol mol⁻¹) over a full growing season. Soil-water content was measured weekly with a neutron probe. Photosynthesis, transpiration, stonmtal resistance, and intercellular CO₂ concentration were determined with a portable leaf photosynthetic system. Canopy temperature was monitored with an infrared thermometer. Elevated (doubled) CO₂ reduced transpiration rate of big binestem by 25 and 35% under the high- and low-water treatments, respectively. Under both watering regimes, stomatal resistance was greater by ≈1.6 s cm⁻¹ with doubled CO₂ than with ambient CO₂. Plants grown with doubled CO₂ at high- and low-water levels had warmer canopy temperatures (average 1.15 and 0.70 °C warmer, respectively) than plants grown ambient CO₂. Carbon-dioxide concentration did not affect the rate of photosynthesis, even though intercellular CO₂ concentration was increased under high CO₂. Elevated CO₂ did not increase the height of plants grown at the high water level, but it did increase the height at the low water level by an average of 9 cm. This research was supported by U.S. Dep. of Energy Grant No. DE-FG02-84ER60253.A000.
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