Stomatal distribution patterns change according to leaf development and leaf water status in Salix miyabeana

Salix is a pioneer woody plant genus characterized by a strong plasticity in leaf morphology. The aims of this paper were to determine stomatal distribution (1) in mature leaves in response to environmental conditions, and (2) during leaf development. Stomata of abaxial and adaxial faces of mature leaves of Salix miyabeana SX67 (cultivated in short rotation coppice) were analyzed at the end of summer 2012 and 2013 at six locations in Quebec, Canada. Within each site and across the two growing seasons, stomatal density of abaxial faces was diluted by an increase in area of mature leaves due to higher rainfall. For shrubs with more than one growing season, stomatal density of abaxial faces was affected by annual rainfall, independently of site, whereas leaf area was predominantly influenced by site but was also modulated in part by rainfall. The number of stomata per leaf was site-specific, independently of rainfall. These leaves were mainly hypostomatic, although those collected on shrubs during their first growing season after coppicing (i.e. with a high root:shoot ratio) were amphistomatic. Similarly, at early development stages (surface area