Abstract
The seasonal changes of evolution of CO2 from the floor were studied using a mixed forest of coniferous and broadleaf species. The rate of CO2 evolution (Y) in situ changed considerably with soil temperature (T) throughout the year. On the contrary, soil-watercontent (W) was fairy constant and the mean value was 77% to dry soil. The regression equation between Y (g CO2-C /m2/day) and T (°C) was log Y =0.029T -0.28. Q10 obtained from field data was 2.0 together with that obtained from soils measured in laboratory. The amount of respiration of plant roots to that of forest floor was 13% in March and 24% in Autumn. It was considered that most of CO2 evolved from forest floor was due to respiration of soil micro-organisms and animals.
The number of bacteria increased almost proportionally to the amount of glucose added into soil. This indicates that the nutritional minerals such as nitrogen and phosphorus were sufficient in the soil used here. Further, the growth rate at exponential phase was high of 0.71/hr (generation time, 1.4 hr) at 25°C. This shows that the concentration of nutritional minerals in the soil was high enough to support the active growth of the bacteria.
The results of the present experiment suggest that the environmental factors, which control the evolution of CO2 from forest floor, are soil temperature and water soluble organic carbon, but not soil water and nutritional minerals.
