Interspecific variation in Rubisco CO2/O2 specificity along the leaf economic spectrum across 23 woody angiosperm plants in the Pacific islands

Abstract

The coordinated interspecific variation in leaf traits and leaf lifespan is known as the leaf economic spectrum (LES). The limitation of CO₂ diffusion to chloroplasts within the lamina is significant in C₃ photosynthesis, resulting in a shortage of CO₂ for Rubisco. Although Rubisco CO₂/O₂ specificity (S_C/O) should be adaptively adjusted in response to the interspecific variation in CO₂ concentrations [CO₂] 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, CO₂ conductance, leaf protein content, and leaf mass area, across 23 woody C₃ species coexisting on an oceanic island through phylogenetic correlation analyses. A high S_C/O indicates a high CO₂ specificity of Rubisco. S_C/O was negatively correlated with [CO₂] at Rubisco and total CO₂ 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 [CO₂] 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.

Keywords: CO2 conductance; CO2/O2 specificity; Rubisco; leaf economic spectrum; oceanic islands; photosynthesis; protein content.