Fig. 3 Leaf net CO₂ assimilation rate as affected by photosynthetically active radiation (PAR) for barley (open circles), wheat (solid circles), and kochia (solid triangles) when the growing conditions and leaf temperature when gas exchange was measured were (a) 23/19°C day/night, 31°C; (b) 21/17°C day/night, 26°C; and (c)15/11°C day/night, 16°C