森林の土壌呼吸に関する研究 (1) : 土壌呼吸と気温との関係について

Abstract

京大芦生演習林 (京都府北部) および京大上賀茂試験地 (京都市北区) の8つの異なる林地で, アルカリ吸収法によって, 土壌呼吸量を月1回, 通年測定を行なった。土壌呼吸量は温度の上昇にともなって指数曲線的に増大し, 両者の関係は次式であらわすことができる。log Y=aT+b (Y : CO_2g/m_2・day, T : 気温℃, a, b : 常数) 8つの林地について, 常数a, bを比較すると, 一部の林地を除いてaの値の違いはすくなく, ほぼ0. 03の附近にあった。bの値は林分によってことなり, 土壌呼吸量の年間を通じての違いに重要な関係をもっている。年間を通じてのCO_2発生量を計算すると, 8つの林地を通じて2. 6 - 3. 8ton carbon/ha・yearであった。上賀茂試験地のアカマツ林で, 毎月の落葉落枝量と毎月の土壌呼吸によって放出される量との対比を試みた。夏季は林地への有機物の供給量が低下するのに呼吸量は大きく, 損失の方が大きいのに対し, 冬季は逆に供給量の方が多くなる傾向をもっている。土壌呼吸量は同一林分内においてさえ, 局地的に, また比較的短時間にもかなり変化の大きいものである。それには局地的な土壌, 水分条件の違い, 降雨などが関与していると考えられる。年間を通じての土壌呼吸量の精度をあげるためには, 今後さらにこれらの条件の影響についての検討が必要である。

Since the studies on the soil respiration of forests in Japan are very few, it is very hard to get the sufficient knowledges in order to estimate the annual amount of carbon returned from soil to atmosphere. In present experiment, soil respiration was estimated by alkali absorption method at eight different kinds forests; five of them are located in Kyoto University Forest at Ashiu (northern part of Kyoto prefecture) and three of them are located in Kyoto University Forest at Kamigamo (near Kyoto University). The soil respiration increased exponentialy with the increase of temperature (Fig. 2), and the trend could be expressed by the following formula; log Y=aT+b (Y;CO2 g/m2 ･ day, T;air temperature, ℃, a and b ; constant). The value of the constant "a" of almost of all investigated stands centered around 0.03 in spite of the diversity of site conditions (Table 1). There would be a tendency that the change of the rate of soil respiration depending upon temperature was similar in almost all of stands. The values of the constant "b" were quite different for each stand. As there were no remarkable differences in the value of the constant "a" between stands, it could be concuded that the value of the constant "b" and the temperature were effective to the annual amount of carbon dioxide evolved from forest soils. The range of the amount of carbon evolved from soils was 2.6--3.8 ton carbon/ha ･ year in eight investigated stands (Table 3). When compared the soil respiration with litter fall in Pinus densiflora forests in Kamigamo, the amount of litter fall were smaller than that of the soil respiration in summer, and the loss of soil organic matter would be recovered in autum and winter by the larger amount of litter fall. (Table 4).