132 A.Sh. Mamilov et al. Applied Soil Ecology 16 2001 131–139
Dilly and Munch, 1998; e.g. Kandeler et al. 1999 showed that microarthropods did not significantly af-
fect substrate-induced respiration or microbial C, N and P content in the LF layer containing fresh organic
substances but promoted microbial biomass, protease activity and phosphate content in the deeper H layer.
Hence, it is still unclear how microbial growth and predation interact under various environmental con-
ditions.
Therefore, we studied the effect of natural sub- strates with different quality on the outcome of faunal–
microbial interaction, namely microbial suppression and stimulation. The dynamics of bacterial, fungal and
total microbial biomass and respiration rates in the presence of available litter components were deter-
mined with regard to the abundance of the micro- and meso-fauna. Substrates having high nitrogen content
were compared to those containing low or no nitrogen reserves.
2. Materials and methods
2.1. Soil Ten soil samples of 500 g each were randomly
collected around a fir-tree from the A horizon 0–15 cm in a region with predominantly eutric Podzoluvi-
sols FAO, 1988. The subsequently named ‘soddy- podzolic soil’ was located under coniferous forest, in
the Chashnikovo area, close to Moscow, and taken in 1997. After removing large roots and litter fragments,
Table 1 Characteristics of the native and defaunated soils as determined on day zero
Parameters Native soil
Defaunated soil Microbial biomass
a
mg C g
− 1
soil 1125 ± 51
b
1164 ± 47 Water-extractable organic matter mg C g
− 1
soil Non-fumigated soil
171 ± 34 183 ± 42
Fumigated soil 597 ± 43
624 ± 48 Respiration rate mg CO
2
-C g
− 1
per day 42 ± 4
52 ± 4 Numbers of nematodes 10 g
− 1
soil 25 ± 7
Numbers of microarthropods 90 g
− 1
soil Collembola
6 ± 2 Mites
5 ± 1
a
Microbial biomass C was measured by fumigation-extraction, k
EC
= 2.64.
b
Value of the standard deviation n = 3.
the samples were thoroughly mixed and sieved at 5 mm mesh size. Soil samples were afterwards pre-
incubated at natural moisture content 17 of dry mass corresponding 65 WHC in plastic bags for 14
days at 12
◦
C. The soil contained 12.1 mg organic C g
− 1
dry soil, 0.9 mg total N g
− 1
dry soil, had a pH H
2
O value of 4.6 and contents of exchange- able NH
4 +
-N and NO
3 −
-N of 7.2 and 5.8 mg kg
− 1
, respectively.
2.2. Experimental design Glass flasks volume 150 ml were filled with 100 g
of either native or defaunated soil. Available defauna- tion procedures are physical exclusion of the animals
small mesh bags, application of biocides, microwave treatment, deep-freezing in combination with drying
and moist heat treatment. Although these procedures provide sufficient defaunation, they may cause un-
desired and unpredictable changes in soil physical, chemical and microbiological characteristics such
as CO
2
evolution Huhta et al., 1989; Wright et al., 1989.
We used the method of Wright et al. 1989, which was modified as follows. The samples were placed in
a plastic bag in 2–3 cm layers and then heated at 55
◦
C for 5 h. Heating at 55
◦
C for 5 h completely eliminated active forms of nematodes and microarthropods but
did not cause any significant changes in the concen- tration of water-extractable organic matter, microbial
biomass or soil respiration Table 1. In addition, the respiration rate of stored soil, estimated five times
A.Sh. Mamilov et al. Applied Soil Ecology 16 2001 131–139 133
during 11 days, did not change significantly in either the defaunated or the native soil. It varied from 17.3
to 19.4 and 17.7 to 21.4 mg CO
2
-C g
− 1
soil per day in the native and defaunated soils, respectively. Our
defaunation procedure did not completely kill animal eggs but recovery of the animal populations took about
14–25 days, dependent on taxa, and, thus could only have interfered with the results during the final part of
our experiment.
One percent of alfalfa meal with a CN ratio of approximately 32 ww, wheat straw with a CN ratio
of approximately 82 ww, or starch containing no N were added to each microcosm. As a control, native
soil without any amendment was also applied. The experimental flasks were kept in the dark at 23
◦
C for 1 month.
Three replicate samples from each treatment were analysed after 3, 7, 10, 14, 18, 21 and 23 days for
bacterial and fungal and total biomass and respiration rate. The nematodes were counted on days 0, 15 and
23 and microarthropods on days 0 and 23. Only one flask of each treatment was destructively analysed per
sampling date. This was considered to be acceptable since the variation of respiration rate in defaunated and
native soil samples in preliminary experiment did not exceed 3.5 in three independent microcosms over 11
days.
2.3. Bacterial, fungal and total biomass Bacterial, fungal and total biomass C were esti-
mated by the substrate-induced respiration technique following Anderson and Domsch 1973, 1978 and
modified by West 1986. Fresh soil corresponding to 1 g of oven-dry material received A no inhibitor, B
8 mg streptomycin Fluka, C 65 mg cycloheximide Sigma, D streptomycin and cycloheximide, each
dissolved in 1.5 ml of de-ionised water. After 3 h of incubation at 25
◦
C, 8 mg glucose dissolved in 0.5 ml was added to the soil suspension to stimulate respira-
tory response. Soil respiration was determined hourly. Treatment D was applied so as to completely inhibit
the soil microbial communities Mamilov et al., 2000.
The applied concentrations of antibiotics were tested for the selectivity of the inhibition effect. The
ratio A − B + A − CA
− 1
was initially adjusted to 1 ± 0.05.
Total microbial biomass C in the treatments with starch and alfalfa meal was calculated according to
West and Sparling 1986 using the equation, micro- bial C mg C g
− 1
soil = 433 log
10
A ml CO
2
g
− 1
soil per hour + 59.2. The ratio of fungal to bacterial biomass was calculated from the equation A−BA−
C
− 1
. Fungal and bacterial C was calculated on the base of its contribution to total non-inhibited micro-
bial respiratory response. Microbial biomass C in the treatments with wheat
straw was estimated using fumigation-extraction ac- cording to Vance et al. 1987 with a soil-extractant
ratio of 1:4 dry soil equivalent: 0.5 M potassium sulphate solution and a k
EC
factor of 0.33 Sparling and West, 1988. Organic C in 1.6 ml extract was
digested with 2.4 ml 66.7 mM K
2
Cr
2
O
7
dissolved in 15.6 M H
2
SO
4
. Absorbance was determined photo- metrically at 590 nm. Corresponding biomass val-
ues were estimated either by fumigation-extraction with a conversion factor of 0.33 after Sparling and
West 1988, or by substrate-induced respiration with the conversation formula after West and Sparling
1986 as used in our experiments Mamilov et al., 2000.
All respiration measurements CO
2
, including basal respiration, were quantified by gas chromatog-
raphy. The carrier gas was He with a flow rate of approximately 30 ml per minute, and the injector,
column and detector temperatures were 50, 35 and 140
◦
C, respectively. 2.4. Animal extraction
Nematodes were extracted using Baermann funnels from samples containing 10 g of fresh soil. Micro-
arthropods were extracted over four days in Tull- gren funnels containing 90 g of the soil. In the
extracts total numbers of nematodes, Collembola and mites were counted under a light microscope Cairns,
1960.
2.5. Statistics All analyses were performed in triplicate and the
standard deviations of the mean are given in the Tables and Figures.
134 A.Sh. Mamilov et al. Applied Soil Ecology 16 2001 131–139
3. Results and discussion
