The grass response

摘要

The grasses that provide forage for most of the worlds livestock use either the C_3 or the C_4 photosynthetic routes to fix carbon dioxide into carbohydrates. Both routes eventually employ the carbon-fixing enzyme ribulose bisphosphate carboxylase. However, C_4 grasses are more efficient photosynthesiz-ers as a result of their distinct morphology and their use of another enzyme, PeP-carboxylase, before this ultimate step of carbon fixation. On page 202 of this issue, Morgan et al.' describe experiments aimed at assessing the effects on mixed C_3/C_4 grasslands of raised levels of atmospheric CO_2 and higher temperatures, and, crucially, how these conditions might change the plants' water budgets.