The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 331

Table 4.15.1. Total C concentrations in the L layers and O horizons of soils from the 1957
and 1976 fires sites and rates of C accumulation. The mean values are shown with the standard
deviations followed by nin parentheses. Adapted from Haslam et al. (1998).

Site Horizon/layer Total C content (kg C m − 2 ) C accumulation rate (kg C m − 2 year − 1 )

1957 fire L 1.67 (1.26, 21) 0.044

O 8.42 (5.53, 21) 0.22

1976 fire L 0.66 (0.50, 21) 0.035

O Not present Not present

1957 fire site was complete by 1984 (27 years after the fire). In the later
period from 19 to 38 years, the rate of organic matter accumulation was
much greater and exceeded the rate of C accumulation for other upland
sites that had not been subject to severe fires (between 0.0046 and
0.089 kg C m −2 year −1 ; Korhola et al ., 1995) and lowland mineral soils
(between 0.025 and 0.056 kg C m −2 year −1 ; Jenkinson, 1970).

Recolonization by Organisms

The slower initial rate of soil organic matter accumulation was consistent
with slower recolonization by plants over the first few years after the fires
but, by the time we started work at the fire sites in 1996, it was too late to
investigate the development of the pioneer communities. However, at the
fire sites, we undertook a preliminary investigation of the plants and soil
microorganisms as these are, respectively, the major contributors of organic
matter to the soils and important decomposer organisms.
The grasses Deschampsia flexuosa , Festuca ovina , Agrostis capillaris and
Nardus stricta , the rush Juncus squarrosus and the moss Polytrichum commune
established at an early stage (before 20 years) and were replaced over the
subsequent 19 years by Molinia caerulea. These observations are presented
in more detail elsewhere (Haslam et al ., 1999).
The sizes of the microbial communities in soils from the burned sites
were estimated from biomass C measurements made using the glucose-
induced respiration technique (Anderson and Domsch, 1978). In addition
to providing information to complement the total C data above, the
biomass measurements allowed hypotheses about ecological succession
involving soil microorganisms to be tested. Microbial successions in
soil have been investigated by Insam and Domsch (1988), Insam and
Haselwandter (1989) and Anderson and Domsch (1986), who proposed
that the ratio of microbial carbon to total carbon (C mic :C total ) increases
and that the rate of microbial respiration per unit of biomass (respiratory
quotient, qCO 2 ) decreases as succession proceeds. However, some of these