生育開始前の摘葉がアカマツの生長, とくにその年の上長生長におよぼす影響

Abstract

京都大学農学部附属演習林本部苗畑で, 1960年に植付けたアカマツを用いて, 1963年および1964年に, 生育開始前に針葉を100%摘み, 主としてその年の上長生長に対し, 摘葉がどのような影響をあたえるかを調べた｡ 摘葉処理は, 1963年3月15日 (試験I) および4月18日 (試験II) に行ない, その方法は, 試験Iでは, 葉鞘もろとも手でむしる場合と, 葉鞘の部分を残してハサミで切断する2方法を用い, 試験IIでは"むしり"だけ行なった｡ 試験III (1964年1月28日摘葉) では"むしり"の処理を実施した｡ 調査の結果をまとめると次のようになる｡ 1. 摘葉が最も大きく影響した場合の処理木の枯死は, 試験Iでは2摘葉方法ともに各19本のうち1本づつで, 試験IIIでは25本のうち2本であった｡ 試験IIでは, 摘葉した15本のうち1本も枯れなかった｡ すなわち, アカマツでは, 生育開始前で1月下旬より後に, その針葉を全部失なっても枯れることはまれのようである｡ 2. アカマツの上長生長は, 一般に, 京都地方では3月より徐々に開始し, 4月から5月にかけて, その伸長量が最大となり, 5月下旬には大部分の伸長を終る｡ その後, 徐々に伸長し, 6月下旬または7月上旬には上長生長は休止する｡ 3. 新梢の伸長生長に対する摘葉の影響は相当に大きくあらわれ, 伸長量は, 試験Iで無摘葉木と比べて約30%, 試験IIで約66%, 試験IIIで約22%となった｡ すなわち, 早い時期に摘葉したものほど, その年の新梢の伸長量はすくなかった｡ 4. 摘葉木に展開した新しい針葉が, 正常なものに比べて, その長さ, 重量に著しく差があった｡ すなわち, 針葉の伸長が終った8月31日および9月11日に調査した結果, 1本の平均針葉長は, 摘葉木に展開したものは正常なものの約60%しかなかった｡ また, 単位重量当りの針葉長を求めると, 摘葉木の針葉が無摘葉木のそれに比べて, 生重では1.80倍, 乾重では1.88倍となり, 正常な針葉より細いことがわかった｡ しかし, 両者の含水率には, ほとんど差がなかった｡ 5. 針葉長の出現頻度では, 摘葉木は無摘葉木に比べて, 非常に不規則であった｡

It is well-koown that the leaves of trees have a great influence upon the growth of trees. In this report, the author investigated the effects of artificial defoliation before the growing period upon the height growth of Japanese red pine (Pinus densiflora S. et Z.). These investigations were carried out on the nursery of Kyoto University Forest in 1963 and 1964. The treatments of artificial defoliation were practiced on Mar. 15 (Experiment I) and on Apr. 18 (Experiment II) in 1963, and on Jan. 28 in 1964 (Experiment III). These treatments were 100%-defoliation by picking of needles in either case, and in Experiment I leafcutting with scissors leaving the part of leaf-sheath (6 ~ 7 mm) was added. The results obtained from these investigations were as follows : 1. The number of the withering of these defoliated trees was only one among nineteen in each case of two techniques of defoliation in Experiment I, and two among twenty-five in Experiment III. In Experiment II, any of the fifteen defoliated trees did not wither (Table 1). Namely, it seems that Japanese red pine will continue to grow without withering, in the case of 100%-defoliation performed on and after late in January. 2. In general, under the normal conditions in Kyoto, the height growth of Japanese red pine began gradually early in March, and continued till the first week of July. It was remarkable in April-May, and the greater part of the height growth was over late in May (Fig. 1.). 3. These artificial defoliations had the greatest influences upon the height growth of Japanese red pine. That is, the height growth in Experiment I was about 30% as compared with the normal, and similarly about 66% in Experiment II, about 22% in Experiment III (Table 2, Fig. 2). The both techniques of "leaf-cutting" and "picking" seemed to make little difference upon the height growth in the year. Namely, the earlier the defoliated period is, the less the height growth in the year becomes. 4. The new needles elongated on new shoot of defoliated tree were different from the normal on its length and weight. That is, the length of the former was about 60% of the latter. And in point of the needle-length per weight, the needles of defoliated trees were 1.80 times on fresh weight base, and 1.88 times on dry weight base as compared with normal needles (Table 3). Namely, the former was slenderer than the latter. 5. The water contents of the above two groups of needles was almost alike. 6. On the distribution of the needle-length, that of defoliated trees was irregular in comparison with the needles of non-defoliated trees (Fig. 3).