Studies on the Effect of Leaf Boundary Layer Resistance on the Matter Production of Crop. (1) Effects of Wind Direction to Leaf and Angle of Attack of Air to Leaf on the Boundary Layer Resistance of Sweet Potato Leaf Yoshinobu HARAZONO and Kazutoshi YABUKI College of Agriculture, University of Osaka Prefecture, Mozu-umemachi, Sakai, Osaka 591
Table 1. Experimental conditions. Fig. 1. Schematic illustration of the experimental setup for measurements of transpiration and stomatal resistance of sweet potato leaf.
Fig. 2. Relations between boundary layer resistance to water vapor diffusion for the sweet potato leaf and wind speed. The adaxial surface of leaf is coated with OED.
Table 3. Same as Table 2, but for the sweet potato leaves of noncoated with OED. A is the case when the wind blows from leaf front margin to petiole, and B is the opposite.
原 薗 矢 吹:葉 面境 層 と作 物 の物 質 生 産 に 関す る研 究(1) 製 作 した 表 面 はつ や 消 し塗 料 に よ って 粗 く仕 上 げた これ を 回流 水 槽 内 に 固定 し,水 素気 泡 法 を 用 いて 水 流 の 可視 化 を行 い,境 界 層 の構 造 を 解析 した 解 析 は既 報 (矢吹 原 薗,1978;原 薗 矢 吹,1979)と 同様 に写 真 を 用 いて 行 った 模型 実 験 で は風 速30cm/s,80cm/sに 相 当す る水 流 速度 を 設定 し,迎 え 角 α=0,10,20,30 の層流 条件 に つ いて 測定 した 測 定 に際 して は,模 型葉 の 中 央 部 か ら側 端部 ま で流 れ に平 行 な5ケ 所 の 断 面 の境 界層 を 写 真撮 影 し,境 界層 の構 造 を 立 体 的 に解 析 した Fig. 3. Changes in diffusion resistances, when the adaxial surface of sweet potato leaf is coated with OED (1) and non-coated (II). 3 2結 果 一 例 と して,迎 え 角 α=30,風 速U=80em/sの 合 の境 界 層 の構 造 をFig.5に 示 す Fig.5Aは か ら風 が吹 く気 流 方 向(A)に 相 当 し,Fig..5Bは 流 方 向(B)の 場 葉 の 先端 逆 の気 場 合 で ある 双 方 と も模 型 葉 の 中 肋 に沿 っ た 断 面 の 流 れ を 可 視 化 した も ので あ る Fig.5Aで 徴 的 な こ と は,α=30 特 とい う大 きい 迎え 角 にもかか わ らず,模 型葉 の 上 面 側 の 境 界 層 は 下 面 側 と 同 じ 層 流 構 造 で あ り,そ の厚 さ も 下面 側 と同 程 度 に薄 い こ とで あ る (A)の 気 流 方 向の よ うに風 上 側 先 端 が 尖 って い る場 合 に は,模 型実 験 を 行 った 全 て の迎 え 角 流 速 で 中 肋 付 Fig. 4. Relations between diffusion wind speed, for boundary stomata rs. 3.カ resistances and layer rb, and ン シ ョ葉 形 模 型 に よ る境 界 層 の 解 析 カ ン シ ョ葉 の先 端 か ら葉 柄部 へ 向 って 風 が 吹 く場 合 と その 逆 の 場合 とで は境 界 層抵 抗 値 が異 な る こ とが わ か っ た この よ うな境 界 層 抵 抗 値 の差 異 は,気 流 方 向 の変 化 に よ り境 界 層 構造 が 変 化 した た め に生 じた と推 測 され る そ こで,こ れ を確 か め るた め に模 型実 験 を行 った 3.1実 験方法 カ ン シ ョ葉 形 模 型(模 型葉 と略す)は 前 節で 供 試 した カ ン シ ョ葉 と相 似 形 の もの を縮 尺1/2と して ア ク リル板 で -107- Fig. 5. Structures of boundary layer on the sweet potato leaf model under the flow condition of equivalent wind speed U=80 cm/s and angle of attack of air to leaf a=30, which are visualized by the hydrogen bubble technique. A is the case when the flow direction is from leaf front margin to petiole, B is the opposite.
Table 4. Changes in boundary layer resistance to water vapor diffusion with wind direction A, B, wind speed U, and angle of attack of air to leaf. This result for leaf model is equivalent to the case when the adaxial surface of sweet potato leaf is coated with OED. Flow directions A and B are the same that indicated in Table 3.
1) Boyer, J. S., 1970: Differing sensitivity of photosynthesis to low leaf water potentials in corn and soybean. Plant Physiol., 46, 236-239. 2) El-Sharkawy, M, and Hesketh, J., 1965: Photosynthesis among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances. Crop Sc., 5, 517-521. 3) Gaastra, P., 1959: Photosynthesis of crop plants as influenced by light, carbon dioxide, temperature, and stomatal diffusion resistance. Mededelingen Landbouwhogeschool Wageningen, 50, 1-68. 4) Grace, J., 1977: Plant Response to Wind. Academic Press, London, 54-73. 93-101. 8) Jarvis, P. G., Rose, C. W., and Begg, J. E., 1967: An experimental and theoretical comparison of viscous and diffusion resistances to gas flow through amphistomatous leaves. Agric. Meteorol., 4, 103-117. 9) Monteith, J. L., 1973: Principles of Environmental Physics. Edward Arnold, London, 139-149. 10) Parlange, J. Y,, Waggoner, P. E., and Heichel, G. H., 1971: Boundary layer resistance and temperature distribution on still and flapping leaves, 1) Theory and laboratory experiments. Plant Physiol., 48, 437-442. 2) Troughton, J. H., 1969: Plant water status and carbon dioxide exchange of cotton leaves. Aust. J. Sci., 22, 289-302. Summary The values of boundary layer resistances were determined by the measurements of transpiration rate and stomatal resistance for sweet potato leaves under the conditions of different flow directions, wind speeds, and angles of attack of air to leaf. Further the structures of boundary layer were visually analyzed by means of the hydrogen bubble technique of the leaf model whose shape was similar to the sweet potato leaf. The value of boundary layer resistance of the actual sweet potato leaf decreases exponentially according to an increase in wind speed. The value obtained in the case where the wind blew from the leaf front margin to petiole is 2 to 0.6 in wind speed range 30-150 cm/s, which is smaller than that measured in the case where the flow direction was opposite. From the model experiment, it was confirmed that the differences in the structure of boundary layer. The smallest boundary layer
resistance was observed when the sweet potato leaf was fixed in a laminar flow at an angle of attack of 30. Almost the same value was obtained when the sweet potato leaf fluttered in a turbulent flow. Above mentioned relationships between the flow condition and the boundary layer resistance hold for the model leaves. Comparison between boundary layer resistance and stomatal or mesophyll resistances seems to reveal that the boundary layer resistance becomes a main limiting factor in photosynthesis when the wind speed is lower than approximately 50 cm/s. Therefore, it is suggested that in the environmental control of protected cultivation it is desirable to provide moderate wind for the purpose of obtaining higher matter production.