Relationship between Leaf Movement of Trifoliolate Compound Leaf and Environmental Factors in the Soybean Canopy : III. Comparisons of micro-environments between the rice and soybean canopy

Abstract

To clarify the effect of leaf movements on the micro-environments inside the soybean canopy, the vertical distribution of several meteorological factors were compared between the rice and soybean canopy. The upper layer of the soybean canopy had higher leaf area density. In the soybean canopy, wind speed, wet filter paper evaporation rate and CO₂ concentration of the air were lower, and dew point temperature of the air was higher, just below the plant cover than the rice canopy. By measuring the wet filter paper evaporation rate and the vapor density difference between the air and the filter paper at each height inside the canopy, boundary layer vapor diffusion resistance (r_a) was calculated. r_a increased with lowering the height above the ground inside the canopy, and decreased at each height with increase in the open field wind speed. r_a was larger in the soybean canopy than the rice canopy due to lower wind speed. The relative wind speed in the upper layer of the soybean canopy became higher late in the morning. It is speculated that wind penetrate into the soybean canopy by the active leaf movement. Diurnal variation of relative light intensity was observed in each height inside the canopy. The light extinction coefficients of the whole canopy decreased as the sun altitude increased, and these changing levels of the soybean canopy were larger all day than the rice canopy. The extinction coefficients in the upper layer of the soybean canopy were smaller during the daytime due to trifoliolate compound Leaf movements. Cleary, sunlight penetrates into the soybean canopy with a decrease in the area of triangle described by the three tips of the trifoliolate compound leaf.