Relationship between Leaf Movement of Trifoliolate Compound Leaf and Environmental Factors in the Soybean Canopy. II. Effects of growth and environmental conditions on diurnal changes of leaf movement.

Abstract

We previously reported a method for measuring trifoliolate compound leaf movement in the soybean plant. Leaflet movement was investigated by measuring the area of triangle described by the three leaflet tips (ΔT), the distance between left and right leaflet tips, and the terminal leaflet inclination angle. Diurnal changes in trifoliolate compound leaf movement were examined with reference to leaf position on the stem, growth stages, weather conditions and soil water deficit. Trifoliolate leaf in the upper layer of the canopy, inclined to the upward in the morning, and ΔT decreased remarkably. Leaflets in the lower layer of the canopy, however, inclined to the downward all day, so ΔT did not change greatly. In clear weather, leaflets moved actively, a great decrease in ΔT was observed in midday compared with cloudy weather, due to higher solar radiation. Hysteresis was found in the relation between solar radiation and ΔT, i.e. leaflet movement was more active in the morning than in the afternoon. Leaflet movement wad most active from the late flowering to pod growth stage, and became less active with increasing plant age. Terminal leaflets were observed to become erect or inverse in response to soil water deficit, when leaf xylem water potential decreased to nearly -1.5 MPa. These results suggest that leaflet movement is mainly affected by the intensity of solar radiation, but its diurnal changes are different with leaf position, growth stage, weather and soil water condition.