The diurnal course of leaf gas exchange of the C4 species Amaranthus retroflexus under field conditions in a 'cool' climate: Comparison with the C3 species Glycine max and Chenopodium album.

The gas exchange of leaves of Amaranthus retroflexus (C4) measured under fluctuating environmental conditions in an experimental garden in Würzburg was compared with that of Glycine max and Chenopodium album (C3). Consistent with previous observations, Amaranthus had higher leaf diffusion resistance than the C3 species and low internal air space carbon dioxide concentration. Due to high photosynthetic capacity, Amaranthus fixed as much carbon during the light as the C3 species, even at low temperatures and low light intensities. Low rates of dark respiration of leaves potentially enhances the ability of Amaranthus to grow rapidly after establishment in a disturbed habitat. The data suggest that some populations of Amaranthus retroflexus are adapted to cool climate conditions but are also able to exploit high temperature situations.