林木落葉の分解について (II)

Abstract

1. 京都大学芦生演習林でスギ, ブナ, ミズナラの3樹種について, スギ林, ブナ林, トチ･ミズナラ混交林, 裸地の4つの異なる場所での分解速度を比較した｡ 2. 分解速度は, はやかつたものから順にミズナラ, ブナ, スギの順で, 分解のおこなわれた場所の差よりも樹種による違いのほうがはるかに大きかつたから, この順位は環境の違いによつて変らなかつた｡ 3. ミズナラ落葉は2カ年, 積算温度で約6, 500~7, 300℃, ブナ落葉は約3年, 積算温度で約9, 700~11, 000℃, またはそれ以上, スギ落葉では約4年, 積算温度で約13, 000~15, 000℃, またはそれ以上を必要とすると思われる｡ なお, 18カ月を経過するとスギ落葉はほぼF層の組成に近似し, ブナ落葉はH層のそれに近似した組成をもつようになる｡ 4. 3樹種落葉の各有機組成分の分解を比較すると, スギ落葉では分解の進むにつれてリグニン, 粗蛋白質の絶対量の増加がおこり, ヘミセルローズ量はほとんど減少しなかつた｡ このことはブナ, ミズナラ落葉の場合と著しく異なり, スギ落葉の分解のおそいことは窒素量の乏しかつたことのほかに, これら3組成分の分解に対する著しい抵抗性によるものと考えられる｡ なお, スギ落葉でアルコール･ベンゼン抽出物の量はブナ, ミズナラ落葉に比べて多いが, この組成分はさかんに分解をうけており, スギ落葉の分解を積極的に抑制していたものとは思えない｡ 落葉の分解速度には有機組成の量的な差異のほかに, 有機組成の質的な違いが関係するであろう｡ 5. 分解速度に関係する環境の影響は本実験条件下では主として水分条件の違いによるものと思われ, 沢沿いのトチ･ミズナラ林で最もはやく, スギ林, ブナ林ではおそかつた｡ 環境の違いによる分解速度の差異は, 樹種の違いによるそれより大きくはなかつた｡ なお, 同一樹種内で環境の違いによつて分解速度に違いを生ずるが全有機物の分解に応ずる各有機組成の分解の割合には変化がないようであつた｡

1) This report deals with the rate of decomposition of forest litter in Ashiu Forest of Kyoto University (mean annual temperature, 11.4℃, annual precipitation, 2781mm). The materials used were Sugi (Cryptomeria japonica) litter, Buna (Fagus crenata) litter and Mizunara (Quercus crispula) litter. These litter were placed on the ground in the following four different site: Sugi site (south aspect, altitude about 650m, BD-d Soil), Buna site (west aspect, altitude 900m PD III soil), Mizunara site (lower slope of valley, altitude 650m, BE soil), Open site (south-east aspect, altitude 650m, BD-d soil). 2) When the rate of decomposition of forest litter were arrenged in order of decreasing rate, the order became Mizunara, Buna and Sugi, in all site tested (Fig. 1, Table 1). 3) The time necessary for the disappearances of litter materials by decomposition were estimated. These were as follows: Mizunara litter, about 2 years (integrated temperature is about 6500~7300℃), Buna litter, about 3years (integrated temperature is abovt 9700~11000℃) or more, and Sugi litter, about 4 years (integrated temperature is about 13000~15000℃) or more. 4) According with the progress of decomposition, the lignin and crude protein fraction steadily decreased, and hemicellulose fraction also decomposed very rapidly in Mizunara and Buna litter. As regards Sugi litter, lignin and crude protein fraction were not decreased quantitativly, but increased with the progress of decomposition, and hemicellulose fraction was only slightly decreased (Fig. 2). It seemed that the slower rate of decomposition of Sugi litter were due to the very slow rate of decomposition of lignin, crude protein and hemicellulose fraction. The amount of alcohol-benzen soluble fraction of Sugi litter was about twice as much as Mizunara and Buna litter. But this fraction was rapidly decomposed in Sugi litter, and so it seemed that this fraction did not inhibit the decomposition of Sugi litter. The rate of decomposition of forest litter may be influenced by the quali tative differences of each organic composition between tree species, as same as by the quantitative differences. 5) The rate of decomposition of forest litter varied by the environmental factors. In all species tested, the litter decomposed most rapidly in Mizunara site, and usualy slow in Sugi or open site, since the Mizunara site was located on BE soil type and its moistare condition was most favarable. In Sugi or Open site, the decreased rate of decomposition were as follows: Sugi litter, about 50%, Mizunara and Buna litter, about 65%. (% based on the total amount of decomposition in Mizunara site)