ササの生理, 生態に関する考察

Abstract

京都大学上賀茂育種試験地に自生しているメダケ属に属するケネザサ (Pleioblastus pubescens Nakai) を用いて, その生理, 生態を調べ, 併せて刈払の時期別試験を行い, ササ地取扱上の参考資料とした｡ その実験結果について要約すれば, 1. ケネザサの成長経過は4月上旬に筍が地上に現れ, 伸長の速度を高めて5月中旬に最盛期に達し, 以後漸次成長が衰え, 7月上旬に成長を終える｡ この成長期間はおよそ60~80日間であり, それと前後して新しく地下茎が伸びはじめ8月上旬に伸長最盛期を生じ, 11月上旬に成長を終る｡ 2. 幹に含まれる貯蔵澱粉の動きについては, まず減少する時期をみると, 春季の幹 (筍) 伸長最盛期ならびに夏季の地下茎伸長期において最も顕著である｡ しかしその年発生した新ザサは新葉を着生する迄澱粉粒を認めず, 成長のエネルギーは地下茎の貯蔵養分あるいは前年生 (母竹) の同化物質に依存するものと思われ, 新葉をだせば自己の同化作用により, さらに伸長を促進させ, しかる後貯蔵澱粉の蓄積がみられる｡ 3. 地下茎に含まれる貯蔵澱粉の動きについてはおよそ地上茎 (幹) と同じ経過をたどるが, 年齢によつて多少趣を異にする｡ 例えば1年生地下茎についてはその先端近くの芽が伸びて新地下茎となるので, 伸びはじめの頃は2年生地下茎よりも多くの澱粉が貯蔵されていることが認められる｡ 4. 11月以後の成長完了後においては同一年令の幹および地下茎では幹の大なるもの程貯蔵澱粉が多いが, 春季の活動前に差を生ずる｡ 5, 成長完了後における1年生地下茎の貯蔵澱粉は当年生の幹に含まれている貯蔵澱粉よりも常に多い｡ 6. 成長期における貯蔵澱粉の増減は成長のみられぬ時期に比較して活発である｡ 7. 全面刈払による影響は4月刈払を行うと間もなく発生する新ザサに現れ, 7月, 8月, 10月, 12月刈払においては翌春発生する新ザサに現れる｡ そして刈払の時期別試験によると, 新ザサの発生に最も悪い影響を与えるのは地下茎の伸び盛りの7~8月における刈払であり, これらの区においては枯死せる地下茎も多い｡

Sasa (bamboo grass) is generally used to sasapulps, furnitures, and preies of domestic animals etc., but it grows in forest ground as land plants and frequently obstructs growth of planted tree. Therefore, treating sasa, we should have their physicological and œcological learning, but today, literature which are known to us about it, are the seasonal changes of reserve starch in bamboo rhizome, so authers test it by chief use of kenezasa (Pleioblastus pubescens Nakai), that is to say, this test consists of three parts, the first is relation of growth and atsmospheric phenomena, the second is not only growing process, but year distinction of bamboo stem and rhizome on the seasonal change of reserve starch by the microchemical method, and the last, as their apprication, is prsperity of weeding season in forest ground. The results by this studies are as follows: 1. About growing process of Kenezasa, bamboo shoot sprout out of the ground early in April, and attain to maximum growth period with promoting elongation about the middle of May, from that time gradually waste away the growth, at last the growth of bamboo stem comes to an end early in July. This growth period is from 60 to 80 days, closely one upon the other, new bamboo rhizome begin to grow and atain to maximum growth period early in August, at last the growth of bamboo rhizome comes to an end early in November. Regarding to the growth of Kenezasa and atomospheric phenomena, bamboo rhizome relats to temperature what bamboo stem relats to quality of precipitation. 2. The decrease of reserve starch in bamboo stem is most visible to growth period in bamboo rhizome and to its maximum growth period on bambo shoot, but this year stem (growth in 1955) could not recognize reserve starch before new leaves, and its energy seems to request the reserve nutrition of bamboo rhizome and the assimilated material of last year stem (growth in 1954 or till then). Towards growth period of bamboo stem, new leaves make of assimilation starch with themselves and by the assimilation starch their elongation is promoted, and then begins accumulation of reserve starch. 3. Reserve starch of 2nd year rhizome (growth in 1953) decreased in growth period of bamboo stem and rhizome as well as reserve starch of bamboo stem. However, especially when bamboo rhizome begins elongation, the quantity of reserve starch which is observed in rhizome of 1st year is more than rhizome of 2nd year. 4. After growth period--autumn--in bamboo stem and rhizome of the same year, the larger bamboo stem is, the more reserve starch, and the difference of reserve starch is recognized visible before growth period in spring. 5. After growth period reserve starch of 1st year rhizome has usually more than reserve starch of this year stem. 6. At growth period increase and decrease in reserve starch as compared with resting period is inactivity. 7. According to the seasonal test of weeding, it is the plot which put to the test in elongational period that recovery conditions of Kenezasa is the most influenced, and besides there are many withered bamboo rhizome.