Soil respiration was measured throughout the year (June 1992 to May 1993) in a mature, deciduous, broad-leaved forest and an adjacent, clear-felled stand which was made in November 1991, in Hiroshima Prefecture, west Japan. The same soil temperature and soil moisture content as those in the forest stand were maintained in two frame boxes covered with sheers of white netting in the dear-felled stand to observe soil respiration. A herbicide was applied to the cut end of all stumps in one of the two frame boxes in order to kill the root system. There was no significant difference in the aboveground biomass and soil environmental conditions between the forest and the frame boxes in the clear-felled stands. The difference in soil respiration rate between the forest and the frame box, in which the root system was killed by the herbicide, was considered to be due largely to the contribution of root respiration. Taking into consideration CO 2 evolution due to the decomposition of roots killed and the change in A o layer respiration rate after clear-felling, the proportion of root respiration to the total soil respiration before dear-felling was estimated to be 5 i% annually, which coincides closely with those values estimated previously in mature forests by other methods. The difference in the soil respiration rate between the two frame boxes (one with killed roots and the other with undisturbed roots) suggested that the annual root respiration rate just after clear-felling dropped to about two-thirds (70%) of that before clear-felling.

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Microbial characteristics of soil are being evaluated increasingly as sensitive indicators of soil health because of the clear relationship between microbial diversity, soil and plant quality and ecosystem sustainability. This study aimed to determine microbial carbon biomass and microbial abundance after fire to estimate the degree of damage, including the rate of recovery of micro‐organisms, in each area. The study also aimed to establish relationships between microbial biomass and microbial abundance and the physico‐chemical properties of the soil. The study was conducted in three different study areas in Hiroshima prefecture, one unburned area and two burnt areas (one immediately after and one 2 years after fire). anova showed a significant difference in microbial carbon biomass and microbial abundance among the study areas. Microbial carbon biomass and microbial abundance were highest in the unburned area, followed by the area burnt 2 years ago and lastly by the area studied immediately after fire. Carbon biomass was highly correlated with microbial abundance (r2 = 0.950). Carbon biomass and microbial abundance were shown to be significantly correlated to the soil's physico‐chemical properties, such as pH, moisture content, water‐holding capacity and carbon : nitrogen (C : N) ratio. However, the C : N ratio was closely correlated to both carbon biomass and microbial abundance with r2 = 0.705 (P < 0.01) and r2 = 0.560 (P < 0.01), respectively.

In order to clarify the role of micro‐organisms in the carbon cycle of the boreal forest ecosystem, the vertical distribution of soil carbon, soil microbial biomass and respiratory activity was studied in a black spruce forest near Candle Lake in Saskatchewan, Canada. The total amount of carbon contained in moss and soil layers (to the depth of 50 cm beneath the mineral soil surface) was 7.2 kg m−2, about 47% of which was in the L and FH horizons of the soil. Soil microbial biomass per dry weight of soil was largest in the L horizon, while the biomass per ground area was largest in the FH horizon. Soil respiration rate, measured using a portable infrared gas analyzer, was highest in the FH horizon, exceeding 50% of the total soil respiration. Low but significant CO2 emission was detected even in deeper soil horizon (E horizon). We also examined the respiration rate of cut roots and the effect of root excision on respiration. The contribution of root respiration to total soil respiration, calculated from root biomass and respiration rate of cut roots, was about 54%. The amount of carbon evolved through microbial respiration during the snow‐free season ( June–October) was estimated as 221 g C m−2. Micro‐organisms in the L horizon showed high respiratory activity as compared with those in deeper soil horizons.