Responses of Tall Fescue Leaf Meristems to N Fertilization and Harvest Frequency1

Abstract

Leaf elongation rate (LER) of tall rescue (Festuca arundinacea Schreb.) and other forage grasses is known to be modified by management practices. Our objectives were to estimate the influence of harvest frequency and N fertilization on cell division, cell elongation, and other associated cellular changes that collectively result in the modified LER of tall rescue. In two experiments, LER was estimated, then length of epidermal cells was measured at 2 mm intervals from the base of the elongating leaf throughout the leaf intercalary meristem. Using mature epidermal cell lengths and number of epidermal cells in the intercalary meristem, several calculations were made to assess the relative cellular responses influencing LER. In Exp. I, field plots of two genotypes selected for low (LYT, slow LER) or high yield per tiller (HYT, rapid LER), were clipped at 2‐ or 6‐week intervals. The 30% higher LER of plots cut at 6‐week intervals relative to plots cut at 2‐week intervals could be attributed to a 17% greater increase in mature epidermal cell length and a 14% increase in the number of cells matured per day per cell column. In Exp. II the same genotypes were grown in controlled‐environment chambers with two rates of N. The 89% greater LER of plants receiving the equivalent of 336 kg ha−1 N could be accounted for by a 90% increase in the number of epidermal cells matured per day per cell column when compared to plants receiving 22 kg ha−1 N. Cells within the intercalary meristem of plants receiving high‐N also elongated 22% faster than those receiving low N. Lengths of leaf intercalary meristems removed from plants harvested at 2‐week intervals or receiving 22 kg ha−1 N tended to be shorter than those removed from plants harvested at 6‐week intervals or receiving 336 kg ha−1 N. Averaged over treatments within each study, LER of the HYT genotype exceeded that of the LYT genotype by about 50%. This genotypic difference in LER could be attributed to a 28% greater increase in epidermal cell length and a 22% increase in number of epidermal cells matured per day per cell column of the HYT genotype when compared to the LYT genotype. Increased LER due to genetic selection or infrequent cutting was associated with increased rate of cell production and increased cell length, whereas increase due to N‐fertilization was due only to increased cell production.