LEAF MOVEMENT OF BUSH BEAN - A BIOMETEOROLOGICAL PERSPECTIVE

Leaf movements of bush bean plants were studied at the relatively low photon flux density of 0.2 mmol/m(2) per s, and air temperatures of 25 degrees and 35 degrees C in a growth chamber. A beta-ray gauge system was used to monitor continuously pulvinus water status and bending. L eaf angles were below the horizontal and were linearly related to the soil water content (R greater than or equal to-0.91 at 25 degrees C an d R greater than or equal to-0.93 at 35 degrees C). The beta-ray trans mission maxima coincided with the stem temperature minima in darkness and vice versa when brightness prevailed as the growth chamber tempera ture varied with the photoperiod. Leaf angle increased linearly with i ncreased beta-ray transmission. The Q(10) temperature coefficient, a m easure of the metabolic energy requirement for leaf movement between 2 5 degrees and 35 degrees C was estimated at 1.8, and the corresponding mean Arrhenius constant at 423 kJ/mol for bush bean.