Abstract
Mesophyll conductance (g (m)) has received over time much less attention than stomatal conductance (g (s)), although it affects leaf photosynthesis to about the same extent as stomatal conductance does. The objective of this study was to analyze the g (m) trend in five understory herbaceous species growing in a close-canopy forest in the north-west of Italy. In particular, three of analyzed species were monocots: Carex brizoides Lam., Carex pilosa Scop., and Oplismenus undulatifolius P. Beauv and the others dicots species: Circaea lutetiana L., and Pulmonaria officinalis Ced. The results showed, on one hand, the absence of correlation between g (m) and the considered environmental variables in the forest understory (i.e. air temperature, photosynthetic photon flux density and carbon dioxide concentration). Moreover, we carried out a principal component analysis considering all the analyzed morphological and physiological variables for the five species. The following correlation between the first component, related to the leaf mass per unit of leaf area and the leaf tissue density, and g (m) seem to suggest a key role of the leaf structural features in determining g (m) variations across the five species.