Field Studies of Cereal Leaf Growth

Abstract

Throughout winter and early spring, rule and auxanometer measurements showed that leaf extension rate (R_E) was directly related to temperature and stopped at about 0°C. During this period, both night and day time R_E responded similarly to temperature. Bright sunshine in late April and May caused fast transpiration which was associated with low leaf water potential (Ψ) and slow R_E. When bright sun was obscured by cloud, R_E increased but this did not compensate for previous slow R_E. Leaf turgor potential, calculated as the difference between Ψ and leaf osmotic potential, was large (0.6–1.8 MPa) and bore little relation to R_E. Low Ψ was associated with slower R_E than would have been expected without water stress, but the relation was not unique. On a bright day in May, adaptation to low Ψ occurred and during the afternoon R_E was faster than at similar values of Ψ and meristem temperatures before noon. The response of R_E and duration of leaf extension to temperature suggested that for any particular leaf grown under field conditions, variation in mean growing temperature would affect final leaf length only slightly. Because severe water stress slows R_E without affecting the duration of leaf extension markedly, it decreases final leaf size.