落葉落枝の分解にともなう養分量の変化

Abstract

1. 落葉落枝の分解の速さは同一林分では材料の種類によって異なるであろうとして, 滋賀県桐生町のアカマツ林で本実験を行なった。その結果8ヵ月間の重量減少でみた分解速度はヒメヤシャブシ55. 8％, アカマツ葉35. 8％, 幹16. 5％, 枝14. 2％, 皮11. 7％の順であった。そしてこの分解量を残存率で示すと, それと積算温度とは指数関数を満足する関係が成立した。分解速度は材料によって異っていたが, 同時に同一材料の分解の速さも常に一定ではなく分解にともなって徐々に小さくなるようであった。2. リター中の養分量は分解にともなって一般に減少するが増加するものもあった。その減少の度合を重量減少との関係でみると, 材料による違いはあまり見られなかった。そして養分による違いが認められた。リター中の養分は分解に伴って減少し, その養分減少の速さは非常に速いNa, Kと, やや速いMg, Caと遅いP, Nの三つに分けることが出来る。この中でNはリターの分解の速さよりも遅く, Pは同じくらいの速さで減少した。またNa, K, Mg, Caはかなり速く2 - 3倍の速さで減少した。3. 雨水による溶脱されやすさはNa>Mg≧Ca≧N≧Pの順であり, Kはアカマツ葉でNaに次いで溶脱されやすかった。他の材料ではKは溶脱されやすさが割に小さかったが, これは落葉材料の初期条件の違いが関係しているのであろう。

1. This experiment was performed in a pine (Pinus densiflora) stand at Kiryu in Ōtsu City in Shiga Prefecture on the supposition that the rate of decomposition of litter would be due to differences in the make-up in the same stand. In an eight-month study from April 23 to December 14 in 1968, the results showed that the rate of decomposition of dry matter was 55.8% in Alnus pendula leaves, 35.8% in Pinus densiflora needles, 16.5% in pine stems, 14.2% in pine branches, and 11.7% in pine bark. When the amount of this decomposition was calculated by the rate of remaining litter, the exponential relation between accumulated temperature and the rate was apparent. The rate of decomposition was influenced by the difference of litter make-up. Although the litter make-up may have been similar, the decomposition rate varied. As the decomposition progressed, the rate seemed to decrease. 2. As decomposition progressed, the amounts of nutrients in the litter generally decreased, but sometimes increased. In the relation between the rate of loss of the nutrient elements and the loss of dry matter, the make-up did not seem to be significant. The rates differed according to the nutrient elements. As the litter decomposed, the nutrients contained therein decreased and these elements may be separated into three groups on the basis of rates of loss during decomposition; (1) decomposing very fast, sodium and potassium; (2) decomposing fast, magnesium and calcium; and (3) decomposing slowly, phosphorus and nitrogen. The loss of nitrogen occurred more slowly than the loss of dry matter, and the loss of phosphorus was at the same rate as the dry matter. Sodium, potassium, magnesium and calcium decreased at rates twice or three times as fast as the dry matter. 3. The nutrient elements were leached in the following order of speed Na>Mg≧Ca>N≧P. In pinus densiflora needles potassium was leached at a rate after sodium. In other litter mak-up, potassium was not leached at this rate, but this may be due to differences in conditions, make-up, decomposition and other factors inherent at the beginning of the investigation.