樹木水耕に於ける通氣量の影響

Abstract

水耕に際し同一の水耕液を使用せる場合も通氣の程度によつて植物の生育に著しい相違を見る場合があるが, 之等の事實に就て, ヒノキ, フサアカシア及びアイグロマツを用いて實驗した結果次の樣な事が認められた｡ 尙水耕液はOLSON氏液及び芝本氏液 (共に假稱) を用いたが, 前者はアイグロマツに對しては不適であり, フサアカシアに對しては後者よりも稍々劣り, ヒノキに對しては兩者による差異を認めなかつた｡ (1) ヒノキに對しては通氣一日二回, 各回0.25立乃至2.00立の間では通氣量の差は地上部の生育には殆んど相違を現さないが主根の發育には相當の影響を與え, 通氣量0.5立 (通氣後15.5時間の酸素含有量16.06 ~ 22.41, 平均18.76p.p.m/cc.) の附近より減少すると主根の伸長は急に減退する｡ 而してその際, 主根基部附近より分岐する根を增加する｡ 之は液中酸素の含量低下に伴い, 液の表面に接する空氣より溶解する酸素の利用に對する適應と見る事が出來よう｡ 通氣量を0.5立以上に增加した場合は通氣量による影響は著しくない｡ 換言すれば此の附近に根の酸素要求濃度の最小限度があると思われる｡ (2) フサアカシアに對しては通氣量は地上部及び根の双方に對して顯著な影響を及ぼし通氣量0.25立乃至2.00立の範圍内に於ては通氣が多くなる程發育が良好であり, 特に根の分岐が旺盛となる｡ フサアカシアの良好なる生育の爲には, 2立 (通氣後15.5時間に於ける酸素含有量16.81 ~ 22.02, 平均18.87p.p.m/cc.) 以上の通氣を必要とすると考えられる｡ (3) 土壤に生育せるアイグロマツを水耕に移した際は, 從來の根は衰退し新根を形成する｡ その發生數及び發生部位に對する通氣量の影響は本實驗では明でないが, 之は試驗期間が短かく, 且秋の休止期に向える爲とも考えられ再試驗を要する｡ (4) 通氣後15.5時間に於ける水耕液中の酸素含有量は實驗期間8月中旬より11月中旬の間に於てヒノキの場合9月末に, フサアカシアの場合10月12日前後に最小量が見られたが, 之は發芽後次第に伸長した之等の稚苗の根の酸素消費量の增加が最大に達し, 後, 秋季に向つて漸減した時期に一致するかと推察される｡ 尤も之には液中に生ぜる少許の藻類の光合成による酸素放出等の因子も多少は關係するであろう｡ (5) 發芽後同一期間を經過したフサアカシアをヒノキと比較すると, 液中酸素の單木當り消費量も, 要求濃度の限界も, 前者が遙に高い點にあると認められる｡

For the sake of deciding the amount of oxigen which is required by seedlings of trees in hydroponic, and, if possible, investigating the rôle of soil-porosity to the growth of trees, these studies were carried out. Results are as follows: -- (1) There is no difference between Shibamoto's and Olson's Solution for the growth of Japanese cypress (Chamacyparis obtusa S. et Z.) but for the growth of Acasia (Acasia dealbata Link.) the former somewhat superior to the latter, and for the growth of pine (Pinus densi-Thunbergii Uyeki) the latter is not suitable. (2) The quantity of oxigen in solution showed minimum value about the end of September and 12th of October respectively in the case of Japanese cypress and Acasia, when the influences of density of air and solubility of oxigen at the time of aeration are eliminated. (3) The various grades of aeration--two times a day, each time from 250 c.c. to 2000 c.c.--give not so much influence upon the growth of tops of Japanese cypress, but upon the roots they give considerable influence, that is, as the volume of aeration decrease, the growth of main root diminish and, at the same time, the roots which diverge from upper part of main root increase their number and length. These influences are conspicuous when the aeration is less than 500 c.c.--at the time of analysis 15.5 hours after aeration, quantity of oxigen in solution is from 16.06 to 22.41, on average 18.76 p.p.m./c.c.--and when the aeration is over 500 c.c., these influences decrease. (table 1) [Table omitted] (4) Corresponding to the grade of aeration, both tops and roots of Acasia show conspicuous distinction in growth. The more the volume of aeration (from 250 c.c. to 2000 c.c.) the better the growth of the plants--length, diameter of stalks, number of leaves, number and length of primary and secondary roots. For the favourable growth of Acasia more than 2000 c.c. of aeration--at the time of analysis the quantity of oxigen in solution is from 16.81 to 22.02, on average 18.87 p.p.m./c.c.--is required. (table 2) (5) When pines are transplanted to hydroponic from nursery, their old roots seem to stop their growth and form new roots. The relations between number, length and diverging portion of new roots and the grade of aeration could not evidently obtained. (6) About the amount of consumpted oxigen per one seedling, Acasia surpass Japanese cypress, and the more prosperous the growth of plant the more oxigen they consume.