Growth of tall fescue leaf blades in various irradiances

Abstract

Information on the effect of irradiance intensity on grass leaf development and spatial distribution of growth is essential to understand the ecology of grazed grasslands. Our objective was to determine how decreasing or increasing irradiance altered elongation and spatial distribution of growth in leaf blades of tall fescue (Festuca arundinacea Schreb.). Three experiments were conducted in growth chambers. In Experiment 1, plants of a low yield per tiller genotype were grown sequentially under decreasing photosynthetic photon flux densities (PPFD ; 400–700 nm) of 550, 190, 50, or 0 μmol m−2 s−1. In Experiment 2, the same plants were grown under increasing PPFD of 50, 130, and 400 μmol m−2 s−1. In Experiment 3, the low yield per tiller genotype and a high yield per tiller genotype were grown under decreasing PPFD of 600, 300, 50, and 0 μmol m−2 s−1. The elongating leaf was measured daily from its tip to the collar of the most recently expanded leaf. Leaf elongation rate was calculated as the linear regression coefficient of leaf length versus time. The spatial distribution of growth in the elongating leaf was determined by measuring short-term displacement of holes pierced through the basal 30 mm. Leaves of the high yield per tiller genotype elongated 40 per cent faster than leaves of the low yield per tiller genotype. The growth zone of elongating leaves was longer at low irradiance, 24 mm versus 18 to 21 mm at high irradiance. The spatial distribution of growth was displaced along a greater length of the elongating zone at low irradiance, whereas at high irradiance elongation was concentrated nearer the ligule. Both genotypes responded in a similar pattern to altered radiation density although there were differences in level of response.