Stomata morphological traits in two different genotypes of Populus nigra L.

Populus nigra L. (black poplar) possesses amphistomatic leaves, with large (giant) and normal sized stomata. The role of giant stomata in leaf development, and the consequences on stomatal density in adult leaves remains elusive. This paper describes the characteristics of ordinary and giant stomata in leaves of two black poplar genotypes (58-861 with large leaves from northern Italy, and Poli with small leaves from southern Italy). Stomatal traits in both genotypes were studied using light microscopy on mature leaf adaxial and abaxial epidermal impressions. Moreover, scanning electron microscopy was applied to study giant and normal stomata in early, young, and mature leaves. Leaf abaxial surfaces in the two genotypes revealed variable sizes and patterns of stomata related to differences in intrinsic water use efficiency (Wi). These observations provided evidence of different stomatal types in mature black poplar leaves, and new information regarding the presence and potential role of giant stomata in black poplar leaves.