Contrasting Anatomical and Biochemical Controls on Mesophyll Conductance Across Plant Functional Types

Mesophyll conductance (g ) limits photosynthesis by restricting CO diffusion between the substomatal cavities and chloroplasts. Although it is known that g is determined by both leaf anatomical and biochemical traits, their relative contribution across plant functional types (PFTs) is still unclear. We compiled a dataset of g measurements and concomitant leaf traits in unstressed plants comprising 563 studies and 617 species from all major PFTs. We investigated to what extent g limits photosynthesis across PFTs, how g relates to structural, anatomical, biochemical, and physiological leaf properties, and whether these relationships differ among PFTs. We found that g imposes a significant limitation to photosynthesis in all C PFTs, ranging from 10-30% in most herbaceous annuals to 25-50% in woody evergreens. Anatomical leaf traits explained a significant proportion of the variation in g (R  > 0.3) in all PFTs except annual herbs, in which g is more strongly related to biochemical factors associated with leaf nitrogen and potassium content. Our results underline the need to elucidate mechanisms underlying the global variability of g . We emphasise the underestimated potential of g for improving photosynthesis in crops and identify modifications in leaf biochemistry as the most promising pathway for increasing g in these species.