| トウモロコシの根表面積が水吸収および蒸散に及ぼす影響. The effect of root surface area on the water uptake and transpiration rate of maize plants | |||||||||||||
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| 本研究では植物の水吸収および蒸散に及ぼす根表面積の影響を理論的に誘導し, 実験で検討した.その結果は以下のように要約できる.1.報告された根の吸水機構と流体力学的方法に基づき, 根の表面積と水吸収関係の理論モデルを構築し得た.2.根表面積が少なくなると, 根の吸水抵抗が大きくなり, Esは小さくなるが, 単位根長当たりの吸水速度は大きくなることが分かった.根表面積が少ない個体は根表面積が多い個体より水ストレスを受けやすいことも明らかとなった.3.気象要素はEsに大きな影響を及ぼすことが分かった.日射量が多くなり, 気温が高くなる時, 植物の蒸散は促進され, 日射量は気象要素の中で, 最も重要な要因であることが明らかとなった.4.葉面積/根表面積および気象要素がトウモロコシのEsに及ぼす総合的な影響を考察して, Esを算定できる重回帰式が導かれた.5.本研究では, 土耕の個体は水耕の個体より最大Esが大きかった.また, 土耕の個体は水耕のものより正常な生長を満たすのに必要な根表面積が多い.土耕および水耕とも, 葉面積/根表面積の増加に伴って, 個体の吸水能力が低下することが明らかになった.. According to the reported mechanism of water uptake and hydromechanical methodology, a theoretical model showing the relationship between the water uptake, transpiration rate and root surface area was developed. The effect of root surface area on water uptake and transpiration rate of maize (Zea mays L. cv Honey Bantam) plants cultivated hydroponically and in soil was examined using this model. Transpiration rate of the plants was measured by load cell using gravity method. Root length was measured according to Newman [10]. Root volume was measured by putting the roots into a measuring cylinder containing water. Water movement coefficient of root system was estimated using pressure chamber method. Regardless of cultivation methods, transpiration rate was low for plants with small root surface area. It was obvious that root surface area had a close relationship with the resistance of water uptake and transpiration rate of the plants. From the measurements of water saturation deficit of leaf, it was clear that plants with smaller root surface area are more sensitive to water stress than those with larger root surface area. Strong correlation between the meteorological conditions and transpiration rate per unit leaf area was observed. High solar radiation led to high temperature, and hence to a high transpiration rate of the plants. Solar radiation is the most important factor among the meteorological conditions influencing the transpiration rate of the plants. A multiple regression equation was obtained for estimating the transpiration rate per unit leaf area of the plants as affected by the ratio of leaf area to root surface area and the meteorological conditions. The maximum transpiration rate per unit leaf area was higher for plants cultivated in soil than those cultivated hydroponically. Compared to plants cultivated hydroponically, plants cultivated in soil needed larger root surface area for their normal growth. Regardless of cultivation methods, water uptake ability decreased with decrease in the ratio of le | |||||||||||||
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