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.