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

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1 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

2 Table 1. Experimental conditions. Fig. 1. Schematic illustration of the experimental setup for measurements of transpiration and stomatal resistance of sweet potato leaf.

3 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.

4 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.

5 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 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.

6 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.

7 1) Boyer, J. S., 1970: Differing sensitivity of photosynthesis to low leaf water potentials in corn and soybean. Plant Physiol., 46, ) El-Sharkawy, M, and Hesketh, J., 1965: Photosynthesis among species in relation to characteristics of leaf anatomy and CO2 diffusion resistances. Crop Sc., 5, ) Gaastra, P., 1959: Photosynthesis of crop plants as influenced by light, carbon dioxide, temperature, and stomatal diffusion resistance. Mededelingen Landbouwhogeschool Wageningen, 50, ) Grace, J., 1977: Plant Response to Wind. Academic Press, London, ) 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, ) Monteith, J. L., 1973: Principles of Environmental Physics. Edward Arnold, London, ) 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, ) Troughton, J. H., 1969: Plant water status and carbon dioxide exchange of cotton leaves. Aust. J. Sci., 22, 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 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

8 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.

九州大学学術情報リポジトリ Kyushu University Institutional Repository 作物の群落構造と物質生産 : 受光および CO_2 拡散 : Ⅴ. グレインソルガムの草高が群落光合成に及ぼす影響広田, 修九州大学農学部栽培学教室武田, 友四郎九州大学農学部栽培学

九州大学学術情報リポジトリ Kyushu University Institutional Repository 作物の群落構造と物質生産 : 受光および CO_2 拡散 : Ⅴ. グレインソルガムの草高が群落光合成に及ぼす影響広田, 修九州大学農学部栽培学教室武田, 友四郎九州大学農学部栽培学教室 Hirota, Osamu Laboratory of Crop Husbandry, Faculty