Field Studies of Cereal Leaf Growth: IV. WINTER WHEAT LEAF EXTENSION IN RELATION TO TEMPERATURE AND LEAF WATER STATUS

Throughout winter and early spring, rule and auxanometer measurementsshowed that leaf extension rate (R_E) was directly related totemperature 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 transpirationwhich was associated with low leaf water potential () and slowR_E. When bright sun was obscured by cloud, R_E increased butthis did not compensate for previous slow R_E. Leaf turgor potential,calculated as the difference between and leaf osmotic potential,was large (0.6–1.8 MPa) and bore little relation to R_E.Low was associated with slower R_E than would have been expectedwithout water stress, but the relation was not unique. On abright day in May, adaptation to low occurred and during theafternoon R_E was faster than at similar values of and meristemtemperatures before noon. The response of R_E and duration ofleaf extension to temperature suggested that for any particularleaf grown under field conditions, variation in mean growingtemperature would affect final leaf length only slightly. Becausesevere water stress slows R_E without affecting the durationof leaf extension markedly, it decreases final leaf size.