Nitrogen Effects on Leaf Anatomy within the Intercalary Meristems of Tall Fescue Leaf Blades

Longitudinal elongation contributes most to leaf area expansion of grasses and its rate is known to be strongly affected by N. Our objective was to determine the effect of two N regimes (N 0 and N+) on the gradient of leaf tissue formation in meristems of two contrasting tall fescue ( Festuca arundinacea Schreb.) genotypes. Proportions of epidermal, mesophyll and vascular tissue as well as intercellular air space were determined throughout the base of actively elongating leaves. The area of leaf transverse sections nearly doubled between the ligule and the distal end of the growth zone (about 30 mm), and was mainly associated with lateral epidermal and mesophyll cell division in the proximal 5.0–7.5 mm. Further increase in transverse area was due to the formation of intercellular airspace and transverse expansion of epidermal cells. Depending on genotype and N treatment the mesophyll, epidermis, vascular bundles and air space comprised 45–54%, 20–28%, 6–9%, and 17–21%, respectively, of transverse leaf area in the distal part of the growth zone. After a slight increase close to the leaf base, the area of vascular tissue remained constant throughout the growth zone. The proportion of air space to mesophyll space was higher at N 0 than at N+ because mesophyll area was enhanced by N+ to a greater degree than by N 0 . In the genotype with slow leaf elongation, the increase in cross-sectional leaf area was due to an increase in both leaf width and leaf thickness. In the genotype which had faster leaf elongation and wider leaves, only leaf thickness was enhanced by N+.