Final published version
Licence: CC BY: Creative Commons Attribution 4.0 International License
Research output: Contribution to Journal/Magazine › Review article › peer-review
Research output: Contribution to Journal/Magazine › Review article › peer-review
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TY - JOUR
T1 - Why is C4 photosynthesis so rare in trees?
AU - Young, Sophie
AU - Sack, Lawren
AU - Sporck-Koehler, Margaret
AU - Lundgren, Marjorie
PY - 2020/8/6
Y1 - 2020/8/6
N2 - 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 the plant kingdom, C4 photosynthesis is notably rare in trees, with true C4 trees only existing in Euphorbia. Here we consider aspects of the C4 trait that could limit but not preclude the evolution of a C4 tree, including reduced quantum yield, increased energetic demand, reduced adaptive plasticity, evolutionary constraints, and a new theory that the passive symplastic phloem loading mechanism observed in trees, combined with difficulties in maintaining sugar and water transport over a long pathlength, could make C4 photosynthesis largely incompatible with the tree lifeform. We conclude that the transition to a tree habit within C4 lineages as well as the emergence of C4 photosynthesis within pre-existing trees would both face a series of challenges that together explain the global rarity of C4 photosynthesis in trees. The C4 trees in Euphorbia are therefore exceptional in how they have circumvented every potential barrier to the rare C4 tree lifeform.
AB - 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 the plant kingdom, C4 photosynthesis is notably rare in trees, with true C4 trees only existing in Euphorbia. Here we consider aspects of the C4 trait that could limit but not preclude the evolution of a C4 tree, including reduced quantum yield, increased energetic demand, reduced adaptive plasticity, evolutionary constraints, and a new theory that the passive symplastic phloem loading mechanism observed in trees, combined with difficulties in maintaining sugar and water transport over a long pathlength, could make C4 photosynthesis largely incompatible with the tree lifeform. We conclude that the transition to a tree habit within C4 lineages as well as the emergence of C4 photosynthesis within pre-existing trees would both face a series of challenges that together explain the global rarity of C4 photosynthesis in trees. The C4 trees in Euphorbia are therefore exceptional in how they have circumvented every potential barrier to the rare C4 tree lifeform.
U2 - 10.1093/jxb/eraa234
DO - 10.1093/jxb/eraa234
M3 - Review article
VL - 71
SP - 4629
EP - 4638
JO - Journal of Experimental Botany
JF - Journal of Experimental Botany
SN - 0022-0957
IS - 16
ER -