Why does C4 photosynthesis rarely evolve in trees?

C4 photosynthesis is an ultra-efficient mode plant physiology that is used by our most productive food and bioenergy crops, including maize, sugarcane, and miscanthus. It has evolved independently in nearly 70 plant lineages. Despite these multiple evolutions, C4 photosynthesis is extremely rare in trees, having only been documented in a handful of tree species in the Euphorbiaceae, a family important for oil and rubber production. This PhD studentship will investigate why C4 photosynthesis rarely evolves in trees. To do this, the student will look at the water- and nitrogen- use economies of Euphorbiaceae trees of differing photosynthetic backgrounds in both greenhouse and field experiments. Field work will take place at the Chinese Academy of Sciences campus at the South China Botanical Garden in Guangzhou, which houses a collection of Euphorbiaceae trees. Through biogeographic analyses of Euphorbiaceae trees with different photosynthetic backgrounds, the student will illustrate how the ecological and geographic distributions of these species may have facilitated the evolution of complex photosynthetic states in this family.