The quantum yield for CO2 uptake in C 3 and C 4 grasses

The quantum yield for CO2 uptake was measured in C3 and C4 monocot species from several different grassland habitats. When the quantum yield was measured in the presence of 21% O2 and 340 cm(3) m(-3) CO2, values were very similar in C3 monocots, C3 dicots, and C4 monocots (0.045-0.056 mole CO2 · mole(-1) quanta absorbed). In the presence of 2% O2 and 800 cm(3) m(-3) CO2, enhancements of the quantum yield values occurred for the C3 plants (both monocots and dicots), but not for C4 monocots. A dependence of the quantum yield on leaf temperature was observed in the C3 grass, Agropyron smithii, but not in the C4 grass, Bouteloua gracilis, in 21% O2 and 340 cm(3) m(-3) CO2. At leaf temperatures between 22-25°C the quantum yield values were approximately equal in the two species.