Relation between the Rate of CO2 Evolution from Soil and the Amount of Dissolved Organic Carbon in Soil Solution

Soils from several forests were sampled, and incubated at 25°C until the direct effects of disturbance by soil sampling were extinguished. The rates of CO2evolution of these soils varied considerably among the soils from different forests. The rates were not correlated with pH of soil, water content, number of heterotrophic bacteria or the amount of total organic carbon, but highly correlated with the amount of dissolved organic carbon in soil solution obtained by a centrifugation at 13, 000×g for 40 min at 4°C.Even in the soil from the same forest, the rate of CO2evolution Y (mg C/kg dry soil/hr) increased rapidly then decreased gradually, when the soil was air-dried and wetted. Whereas, the amount of dissolved organic carbonX (mg C/ kg dry soil) also changed in the same manner, and the relation betweenXandYwas expressed by a simple equation ofY=aXexcept of soils immediately after wetting. The gradient (a) at 25°C differed considerably among the soils from different forests as in 0.355 of Kanto loam soil at Fuchu, 0.077 of volcanic soil at Shikaoi, 0.072 of alluvial soil at Obihiro, 0.131 of volcanic soil at Kagoshima and 0.125 of lime soil at Nago. The reason for the differences of the gradient (a) among the soils from different forests left to be studied.Furthermore, some mutual relations of the rate of CO2evolution were also discussed, the amount of dissolved organic carbon and the amount of hetero-trophic microbes in soil.