Interspecific variation in Rubisco CO 2 /O 2 specificity along the leaf economic spectrum across 23 woody angiosperm plants in the Pacific islands.

The coordinated interspecific variation in leaf traits and leaf lifespan is known as the leaf economic spectrum (LES). The limitation of CO 2 diffusion to chloroplasts within the lamina is significant in C 3 photosynthesis, resulting in a shortage of CO 2 for Rubisco. Although Rubisco CO 2 /O 2 specificity (S C/O ) should be adaptively adjusted in response to the interspecific variation in CO 2 concentrations [CO 2 ] associated with Rubisco, S C/O variations across species along the LES remain unknown. We investigated the coordination among leaf traits, including S C/O , CO 2 conductance, leaf protein content, and leaf mass area, across 23 woody C 3 species coexisting on an oceanic island through phylogenetic correlation analyses. A high S C/O indicates a high CO 2 specificity of Rubisco. S C/O was negatively correlated with [CO 2 ] at Rubisco and total CO 2 conductance within lamina, while it was positively correlated with leaf protein across species, regardless of phylogenetic constraint. A simulation analysis shows that the optimal S C/O for maximizing photosynthesis depends on both [CO 2 ] at Rubisco sites and leaf protein per unit leaf area. S C/O is a key parameter along the LES axis and is crucial for maximizing photosynthesis across species and the adaptation of woody plants.