Why is C4 photosynthesis so rare in trees

摘要: Since C4 photosynthesis was first discovered >50 years ago, researchers have sought to understand how this complex trait evolved from the ancestral C3 photosynthetic machinery on >60 occasions. Despite its repeated emergence across plant kingdom, is notably rare in trees, with true trees only existing Euphorbia. Here we consider aspects of that could limit but not preclude evolution a tree, including reduced quantum yield, increased energetic demand, adaptive plasticity, evolutionary constraints, and new theory passive symplastic phloem loading mechanism observed combined difficulties maintaining sugar water transport over long pathlength, make largely incompatible tree lifeform. We conclude transition habit within lineages as well pre-existing would both face series challenges together explain global rarity trees. The Euphorbia are therefore exceptional they circumvented every potential barrier