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Retrospective analysis of biochemical limitations to photosynthesis in 49 species: C4 crops appear still adapted to pre-industrial atmospheric [CO2]

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<mark>Journal publication date</mark>30/11/2020
<mark>Journal</mark>Plant, Cell and Environment
Issue number11
Number of pages17
Pages (from-to)2606-2622
Publication StatusPublished
Early online date14/09/20
<mark>Original language</mark>English


Leaf CO2 uptake (A) in C4 photosynthesis is limited by the maximum apparent rate of PEPc carboxylation (Vpmax) at low intercellular [CO2] (ci) with a sharp transition to a ci-saturated rate (Vmax) due to co-limitation by ribulose-1:5-bisphosphate carboxylase/oxygenase (Rubisco) and regeneration of PEP. The response of A to ci has been widely used to determine these two parameters. Vmax and Vpmax depend on different enzymes but draw on a shared pool of leaf resources, such that resource distribution is optimized, and A maximized, when Vmax and Vpmax are co-limiting. We collected published A/ci curves in 49 C4 species and assessed variation in photosynthetic traits between phylogenetic groups, and as a function of atmospheric [CO2]. The balance of Vmax-Vpmax varied among evolutionary lineages and C4 subtypes. Operating A was strongly Vmax-limited, such that re-allocation of resources from Vpmax towards Vmax was predicted to improve A by 12% in C4 crops. This would not require additional inputs but rather altered partitioning of existing leaf nutrients, resulting in increased water and nutrient-use efficiency. Optimal partitioning was achieved only in plants grown at pre-industrial atmospheric [CO2], suggesting C4 crops have not adjusted to the rapid increase in atmospheric [CO2] of the past few decades.