Photosynthesis, water‐use and nitrogen relate to both plant height and leaf structure in 60 species from the Mediterranean

Abstract Within individuals and/or species of trees, the structure and gas exchange of sun‐exposed leaves from the outer part of the canopy have been found to relate to sampling height. Across species, the gas exchange of such leaves has been shown to relate to their structure and biochemical composition, but not to canopy height. Why are leaf traits related to height within tree species but not across a broader range of species? And what are the components of leaf structure involved in leaf‐level carbon, water and nitrogen economies? Plant height, leaf mass per area (LMA) and its underlying components, gas exchange, leaf nitrogen and carbon isotopic discrimination were assessed for 60 species from different life and growth forms growing in the Mediterranean, spanning a wide range of height and LMA values. Contrary to previous comparisons across species, our study shows that leaves of tall plants had a high LMA, a high leaf dry matter content (LDMC) and were slightly thicker; their stomatal conductance and photosynthetic rate were low, while their intrinsic water‐use efficiency ( i WUE) was high. LMA was related to all gas exchange variables as well as to leaf nitrogen. These effects were mostly mediated through LDMC, with limited effects of leaf thickness. These conclusions were hardly modified when phylogeny was account for. Across species of varying life and growth forms, leaf functioning relates to both plant height and leaf structure. These results provide a generalization of previous conclusions found in trees at the intra‐individual and/or intraspecific levels. Inconsistencies among previous studies with respect to plant height are likely an issue of context‐dependency, which should be explicitly taken into account for a better understanding of plant form and function. Read the free Plain Language Summary for this article on the Journal blog.