Abstract

SummaryThe effects of changes in humidity on leaf diffusive conductance of Festuca arundinacea cv. SI 70 during a sequence of changes in leaf orientation were studied in a controlled environment cabinet. Reducing the vapour pressure deficit from 0.95 to 0.32 kPa at 25 °C (increasing relative humidity from 70 to 90 %) increased total leaf conductance by 73 %. Leaf orientation markedly influenced the conductance of individual leaf surfaces, the uppermost nearly always having the greater conductance.Total leaf conductance was greater when the ridged adaxial surface was uppermost and, overall, the adaxial surface was more sensitive than the abaxial to humidity and orientation changes. Mean leaf conductance was significantly greater 8 h after the lights were switched on than after 1 and 4 h. Leaves which naturally displayed the adaxial surface upwards had a higher leaf conductance than those in which the abaxial surface was normally uppermost for most of their length.

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