Variability in Populus leaf anatomy and morphology in relation to canopy position, biomass production, and varietal taxon

Twelve poplar (Populus) genotypes, belonging to different taxa and to the sections Aigeiros and Tacamahaca, were studied during the third growing season of the second rotation of a high density coppice culture. With the objective to highlight the relationships between leaf traits, biomass production and taxon as well as the influence of canopy position, anatomical and morphological leaf characteristics (i.e. thickness of epidermis, of palisade and spongy parenchyma layers, density and length of stomata, leaf area, specific leaf area (SLA) and nitrogen concentration) were examined for mature leaves from all genotypes and at two canopy positions (upper and lower canopy). Above ground biomass production, anatomical traits, stomatal and morphological leaf characteristics varied significantly among genotypes and between canopy positions. The spongy parenchyma layer was thicker than the palisade parenchyma layer for all genotypes and irrespective of canopy position, except for genotypes belonging to the P. deltoides × P. nigra taxon (section Aigeiros). Leaves at the upper canopy position had higher stomatal density and thicker anatomical layers than leaves at the lower canopy position. Leaf area and nitrogen concentration increased from the bottom to the top of the canopy, while SLA decreased. Positive correlations between biomass production and abaxial stomatal density, as well as between biomass production and nitrogen concentration were found. A principal component analysis (PCA) showed that genotypes belonging to the same taxon had similar anatomical characteristics, and genotypes of the same section also showed common leaf characteristics. However, Wolterson (P. nigra) differed in anatomical leaf characteristics from other genotypes belonging to the same section (section Aigeiros). Hybrids between the two sections (Aigeiros × Tacamahaca) expressed leaf characteristics intermediate between both sections, while their biomass production was low.