Answers to Figure Legend Questions

FIGURE 5.7 The light saturation level would be lower than the maximum light level the plant experiences because the energy invested in achieving a higher light saturation level might not pay off.

FIGURE 5.10 At low carbon dioxide and high oxygen concentrations, the photorespiratory carbon dioxide loss can exceed photosynthetic carbon dioxide gain. This is because oxygen is taken up to a greater extent than carbon dioxide by rubisco when the ratios of oxygen to carbon dioxide increase.

FIGURE 5.14 Extrapolation of the line used to fit the data to the x axis indicates that the proportion of the grass flora that is C₄ drops to zero when the growing-season minimum temperature is around 4°C-5°C. This would correspond to an average growing-season temperature of 9°C-10°C, which is at or above the growing-season temperatures for boreal forests and tundra shown in the climate diagrams. This result agrees well with the observed lack of C₄ plants in these biomes.

ECOLOGICAL TOOLKIT 5.1 CAM plants exhibit a wider range of δ ¹³C values because some are facultative CAM plants. At some times they use C₃ photosynthesis, but during drier periods they use CAM photosynthesis. The δ ¹³C of their tissues would reflect a mixing of C taken up using both of these photosynthetic pathways.