Linking stomatal size and density to water use efficiency and leaf carbon isotope ratio in juvenile and mature trees

Abstract Water-use efficiency (WUE) is affected by multiple leaf traits, including stomatal morphology. However, the impact of stomatal morphology on WUE across different ontogenetic stages of tree species is not well-documented. Here, we investigated the relationship between stomatal morphology intrinsic water-use efficiency (iWUE=A/gs) and leaf carbon isotope ratio (δ13C). We sampled 190 individuals including juvenile and mature trees belonging to 18 temperate broadleaved tree species and 9 genera. We measured guard cell length (GCL), stomatal density (SD), specific leaf area (SLA), gas-exchange, iWUE and leaf δ13C as a proxy for long-term WUE. Leaf δ13C correlated positively with iWUE for both juvenile and mature trees. Across species, GCL showed a negative and SD a positive effect on iWUE and leaf δ13C of both juvenile and mature trees. Within species, however, only GCL was significantly associated with iWUE and leaf δ13C. Pioneer species (Populus, Prunus, Betula) showed a significantly lower leaf δ13C than climax forest species (Fagus, Quercus, Tilia), but the differentiation was not clear for iWUE. We conclude that GCL and SD can be considered as functional morphological traits impacting the iWUE and leaf δ13C of trees, highlighting their potential for rapid phenotyping approaches in ecological studies. Competing Interest Statement The authors have declared no competing interest.