Evaluation of the soil fauna impact on d
Biol Fertil Soils (1990) 10:163-169
Biology and Fertility
°fSoil
s
© Springer-Verlag 1990
Evaluation of the soil fauna impact on decomposition
in a simulated coniferous forest soil
H. Setfilfi and V. Huhta
Department of Biology, University of Jyv~tskyl~, SF-40100 Jyv~iskyl~i, Finland
Received December 5, 1989
Summary. Long-term experiments (ca. 2 years) were carried out in laboratory systems that simulated the complexity of a coniferous forest floor. The test materials
were partially sterilized by freezing and thawing, and reinoculated with (1) microbes alone or (2) microbes with
fauna. Removable microcosms containing birch litter,
spruce litter, or humus were inserted into a humus substrate. Two experiments used organic matter only, and another included a layer of mineral soil below the humus.
Both were incubated in climate chambers that simulated
both summer and winter conditions. The evolution of
CO2 was measured at regular intervals. In order to determine the C content of the leachates, the macrocosms and
the microcosms were watered periodically.
Soil fauna significantly increased respiration in the
litter, but not in the microcosms containing humus. In the
later phases of decomposition the presence of fauna had
a negative effect. In the total systems the fauna consistently increased the respiration rate. The loss of mass was
greater in the presence of fauna, especially during the
middle phases (5-11 months), but it was higher in the
controls later.
Throughout the whole incubation period the decomposition rate was strongly influenced by the composition
of the animal community. The interpretation of the resuits is affected by the fact that the controls, to which no
fauna had been added, contained dense populations of
microbial feeders (nematodes, rotifers, and protozoans).
Key words: Soil fauna - Decomposition - Raw humus
- Forest soil - Microcosm
-
CO
2
evolution
The soil fauna contributes significantly to the decomposition of dead organic matter, even though in most eco-
Offprint requests to: V. Huhta
systems the fauna is directly responsible for only a few
per cent of the decomposer respiratory metabolism
(Persson et al. 1980). This has been demonstrated in the
field by the traditional litter-bag method (Edwards and
Heath 1963; Seastedt et al. 1983), in combination with selective biocides (Vossbrinck et al. 1979; Seastedt and
Crossley 1980), and in the laboratory (Hanlon and Anderson 1979; Bengtsson et al. 1988; Set~il/i et al. 1988).
In most cases experiments with litter-bags have failed
to show whether the material lost from the bags had actually been decomposed, or had merely been transported
out of the bags by the fauna. Witkamp and Olson (1963)
suggested that the litter-bag method can only give approximate values for actual weight loss and losses of elements. In contrast, laboratory experiments (in which the
element fluxes can be monitored accurately), can be criticized for oversimplification of both biotic and abiotic
factors (Anderson 1978).
Decomposition of organic matter is regulated by interactions between the substrate quality, the biota, and
the microclimate (Swift et al. 1979). Mutual relationships
among the biota, especially between the microflora and
their invertebrate grazers, has also been reported to be extremely important in affecting the degradation processes
(reviewed by Anderson and Ineson 1984; Coleman et al.
1984). In addition, rates of decomposition may be influenced by interspecific relationships within the faunal
component (Kajak and Jakubczyk 1977; Santos and
Whitford 1981; Set~tl~i et al. 1990a).
Thus, to simulate natural decomposition processes in
controlled laboratory conditions, interactions between
biotic and abiotic environments, as well as connections
among the decomposer organisms, should be taken into
account. Our aim was to conduct a long-term laboratory
experiment with a structurally complex substrate in order
to study the role of the fauna in the decomposition processes of coniferous forest soil. Special emphasis was put
on the rate of decomposition in systems with different
faunal communities. Results of the present paper are obtained from the experiments described in detail by Huhta
and Set/il~i (1990).
164
Materials and methods
The experiments were carried out in plastic boxes ( 4 0 × 6 0 c m ; depth
12 cm) in which a simulated coniferous forest floor was created. Leaf
litter of silver birch (Betulapendula), needle litter of Norway spruce
(Picea abies), and raw h u m u s were used as test materials. These were
placed in nylon-mesh baskets in a systematic m a n n e r and inserted into
the substrate h u m u s . The boxes with their contents are termed "macrocosms", and the m e s h baskets containing the actual test materials are
"microcosms". A constant flow of air (30 liters h -1) was maintained
through the boxes. The boxes were incubated in darkness at + 16 ° + 1 °C
except during artificial winters, when the temperature was lowered stepwise (5 °C weekly) to + 1 ° _+1 °C. Three separate experiments were conducted; those with organic matter only are defined as experiments IA
a n d IB, and that with organic + mineral matter as experiment II.
A detailed description of the experimental design a n d procedures is
presented by H u h t a and Set/ila (1990).
The evolution of CO 2 from the macrocosms was measured from the
outgoing air using an infrared C analyzer (URAS 7N). The analyzer was
connected to a microcomputer, programmed to take repeated measurements for 15 m i n and then to change the unit to be measured by giving
a signal to a magnetic valve system.
To measure the respiration of the test materials separately, microcosms were moved into 0.5-liter glass jars equipped with air-tight lids.
During incubation in a climate chamber, a hole in the lid was closed
with a rubber septum. One 5-ml subsample was taken from the air space
with an injection needle at the m o m e n t the lid was closed, and another
after 60 min of incubation. The sample was injected into the analyzer,
and CO 2 production was calculated from the difference between the recordings. After the m e a s u r e m e n t h a d been taken, each microcosm was
returned to its original position in the macrocosm.
In experiment IA, six replicate microcosms of each test material
were measured (three each taken from two macrocosms). In experiments
IB and II, five replicates of each material were analyzed at a time; in
successive measurements they were taken alternatively from two macrocosms until the first destructive sampling, after which only one macrocosm per treatment remained. The units used were the same for all measurements taken during one season.
The cumulative evolution of CO 2 from both the microcosms and
the macrocosms was estimated from successive m e a n values, assuming
a linear change between measurements. F r o m the data on the macrocosm winter respiration (not shown), it was a s s u m e d that the evolution
of CO 2 during the winter periods was ca. 1/6 of that measured in the
s u m m e r periods.
The estimates of faunal respiration were based on the relationships
between body weight and 0 2 c o n s u m p t i o n as given in the literature and
converted to CO 2 production. Data for 02 c o n s u m p t i o n were obtained
from Persson et al. (1980); calculation of the faunal biomass is described in H u h t a and Set/ala (1990).
At intervals of 4 - 6 weeks (excluding the winters) the microcosms
were removed from the macrocosms, a n d irrigated with distilled and deionized water for the analyses o f total C. At the same time the macrocosms without microcosms were watered. The total C in the leachates
was determined with the C analyzer after 50-~tl subsamples were burned
at + 9 5 0 ° C .
A detailed description of the irrigation procedure is presented by
Set~il~ et al. (1990b).
At the end of each s u m m e r season a destructive sampling was carried out using some of the macrocosms. In experiment IA two refaunated and two control macrocosms were sampled after the first season. In experiments IB and II half the units were sampled after the first
season, and the rest after the second season. At each destructive sampling, 10 (experiment IA) or 5 (experiments IB and II) microcosms of
each test material were randomly chosen for determinations of the loss
in mass. The samples in the microcosms were carefully removed and
placed for 7 days in a high-gradient extractor to extract microarthropods, and then weighed after keeping at + 80 °C for 24 h.
During weeks 2 3 - 2 4 and 4 3 - 4 4 the total a m o u n t of h u m i c substances (humic acids and fulvic acids, excluding humines) in the
leachates from the whole macrocosms were analyzed by high-performance liquid chromatography (Knuutinen et al. 1988). The results are
expressed as relative units because there was no reference liquid for the
soil water.
Statistical differences over long intervals were tested by analysis of
variance for repeated measurements. Differences between particular
samplings were tested by analysis of variance or Student's t-test (Huhta
and Set~il~i 1990).
Results
Respiration
There was a significant difference (P< 0.05) in the respiration rate (calculated per unit mass) between the test materials during the whole incubation period (Table 1). For
all treatments and materials there was a trend towards a
lower respiration with time (spruce litter in experiment IA
formed an exception). After each winter period, however,
the amount of CO2 evolved generally increased. The enhanced respiration rates generally took ca. 10 weeks until
a new balance at a lower level was achieved (Fig. l d - g , i).
In the birch litter the respiration was significantly
stimulated in the refaunated units, especially during the
early phases of incubation (experiment IA; Fig. 1 a; Table
1). The same trend continued until the second winter
(week 56) in experiment IB and even longer in experiment
II (Fig. 1 d, e; cumulative values in Table 1). During the
late phases, respiration was generally lower in the refaunated units, although the difference between the controis and the refaunated systems was statistically signifi-
Table 1. Estimated cumulative evolution of C O 2 (mg C g - ~ dry matter) in microcosms containing birch and spruce litter at the time of the final
destructive samplings
Weeks 0 - 1 8
Weeks 0 - 4 7 / 4 8
Birch
Experiment IA
Experiment IB
Experiment II
Spruce
F
C
107 **
.
.
.
.
75
.
.
.
.
Birch
F
C
F
57 ***
42
.
123 **
144"
Weeks 0 - 9 7 / 9 8
Spruce
.
C
F
.
94
111
.
88
68
Birch
C
.
F
.
78
71
.
200
219
Spruce
C
F
C
.
178
176
131
116
125
131
F, refaunated (macrocosms with complex faunal assemblage); C, control (with microbes and microfauna only). * P < 0 . 0 5 , * * P < 0 . 0 1 , * * * P < 0 . 0 0 1 ,
versus control
165
pg.
IA
-1. h-1
IA SPRUCE
BIRCH
***
200.
100-
30-
150.
75-
25"
100-
50'
50,
25"
Z
6
i, ,"l'/°-O'•/§
®
/~HUMUS
IA
2015-
½
8 1'0 1'2 1'4 I'6 1'8
i
g
8
I'0
1'2 1'4 1'6 1'8
Weeks
120"
IB
(~)
100-
BIRCH
100
80-
80-
60-
60
40-
40,
20-
20w
w
g' "2'0
6°1
3'0
t
4'0
sb
II BIRCH
l
t
" f5
8's
9'5
I B sPRucE
60-
W
"2'0
W
3'0
4'0
~@
5'0
80
90 Weeks
8'0
9'0-~ w e ek s
II SPRUCE
40-
20201
,W
,
5
~ e
2"0
3b
4b
IA
W
/
5b
f5
8'5
9'5
z
TOTA L
.÷*-;
A
\;~U"
w
3'0
4 '0
IB+II
40-
®
. ,\j~/T',
w
"~20
5'0
TOTAL
30-
20
20. ÷-t
10
&
6
~
1'0
1'2
1'4
16
18
2b
2'2
Fig. L Instantaneous evolution of CO 2 (pg g-1 dry matter h -1,
means+ SE) from the microcosms (birch, spruce, humus) and macrocosms (total) in three experiments; • - - • , refaunated; O - - 0 , con-
t
W
,/
5 "2'0
2'5
3'0
W
--r/ . ~
35 75
8'0
9'5
9'0 Weeks
trol; asterisks show either significant differences for the whole experiment (at the end of each diagram) or the previous growing period (analysis of variance for repeated measurements); W,, artificial winter
166
cant only in experiment IB (P = 0.009 from week 56 onwards).
A similar pattern between the refaunated and control
units was observed in the spruce litter. From week 1 to 18
(experiment IA) the refaunated microcosms respired significantly more than the controls (Fig. 1 b; Table 1). During the middle phases of incubation there were some differences in respiration between experiments IB and II. In
the former the refaunated spruce litter continued to respire more than the controls, whereas in experiment II the
opposite was true. During the late phase (from the second
winter onwards) in both experiments the amount of CO2
produced was generally greater in the control units
(Fig. 1 f, g; Table 1).
In cOntrast to the litter materials in experiment IA,
respiration activity in the humus was generally higher in
the control microcosms. From week 6 to 18 respiration
measured in the control microcosms was significantly enhanced (P< 0.05 in four recordings out of seven) over the
level in the refaunated units (Fig. 1 c).
Although the effect of the fauna on CO2 evolution
was negative in the microcosms containing humus, it exerted a positive influence on the respiration measured
from whole macrocosms (experiment IA; Fig. 1 h). During 22 weeks' incubation the mean cumulative respiration
was 83.7 g CO2 in the refaunated systems, and 80.3 g in
the controls. The difference was statistically significant
(P = 0.003).
During the middle and late phases of incubation (experiments IB and II) the respiration level remained slightly higher in the refaunated macrocosms than in the controis, although no statistical differences were found
(Fig. 1 i). The cumulative sums of CO 2 produced from
the whole systems during the 97-98 weeks' incubation
were 260 g vs 239 g, and 263 g vs 245 g COz for experiments IB and II (refaunated vs control), respectively.
The contribution of faunal metabolism (estimated at
the time of the samplings) to the total respiration was
more pronounced in the refaunated systems than in the
control systems (Table 2). The most marked faunal contribution was generally a result of the large enchytraeid
Table 2. Estimated total and faunal respiration (Ixg CO2-C g-1 dry
matter h-1) in refaunated and control microcosms with birch and
spruce litter from destructive samplings of experiments IB and II
Refaunated
Birch
Control
Spruce
Birch
Spruce
IB
II
IB
II
IB
II
IB
II
Weeks 47 - 48
Total
Faunal
Faunal (%)
12.9
1.2
9.3
13.1
1.7
12.9
5.9
0.4
6.8
6.8
0.4
5.9
7.6
0.4
5.3
9.8
0.7
7.1
5.5
0.1
1.8
6.9
0.4
5.8
Weeks 97 - 98
Total
Faunal
Faunal (%)
5.5
1.4
25.4
9.3
0.2
2.2
5.2
0.4
7.7
5.7
0.1
1.8
7.6
0.4
5.3
9.3
0.1
0.5
5.7
0.1
1.8
6.6
0.1
1.5
See footnotes to Table 1
Table 3. Cumulative leaching of total C (mg C'microcosm -~) from
microcosms containing birch litter, spruce litter or humus by the end
of destructive samplings
Expt IA
Week 18
Birch
Spruce
Humus
Weeks 47 - 48
Birch
Spruce
Expt IB
F
C
9.6*
15.6
20.4
6.4
17.9
18.6
m
Weeks 97 - 98
Birch
Spruce
F
Expt II
C
F
C
m
m
16.0"
30.6*
26.4
22.2
9.3
27.3
18.4
30.8
23.7
41.2"
33.7
32.3
15.0
37.2
25.3
36.0
Expt, experiment; for other explanations, see footnotes to Table I
populations. In experiment IA, where the populations
were still developing during week 18, the animals did not
account for more than 1.5°70 of the total.
In the total macrocosms the proportion of the total
CO2 production contributed by the fauna was estimated
to be ca. 5O/o in weeks 47-48 and 10% in weeks 97-98.
The microbivorous fauna including nematodes and
rotifers (protozoans not estimated; see Discussion) present in the control macrocosms was estimated to produce
less than 5°70 of the total CO2.
Leaching of C
During the first 18 weeks of incubation, all recordings
showed significantly more total C leached from the refaunated birch litter than from the controls (experiment
1 A; Table 3). However, the leaching from the spruce litter
was generally more pronounced in the controls. C leaching from humus was significantly (P< 0.05) enhanced in
the refaunated units at the two first waterings (weeks 3
and 7), but from week 10 onwards less C leaching took
place in the refaunated units; in two measurements out of
three the release of total C was significantly greater
(P
Biology and Fertility
°fSoil
s
© Springer-Verlag 1990
Evaluation of the soil fauna impact on decomposition
in a simulated coniferous forest soil
H. Setfilfi and V. Huhta
Department of Biology, University of Jyv~tskyl~, SF-40100 Jyv~iskyl~i, Finland
Received December 5, 1989
Summary. Long-term experiments (ca. 2 years) were carried out in laboratory systems that simulated the complexity of a coniferous forest floor. The test materials
were partially sterilized by freezing and thawing, and reinoculated with (1) microbes alone or (2) microbes with
fauna. Removable microcosms containing birch litter,
spruce litter, or humus were inserted into a humus substrate. Two experiments used organic matter only, and another included a layer of mineral soil below the humus.
Both were incubated in climate chambers that simulated
both summer and winter conditions. The evolution of
CO2 was measured at regular intervals. In order to determine the C content of the leachates, the macrocosms and
the microcosms were watered periodically.
Soil fauna significantly increased respiration in the
litter, but not in the microcosms containing humus. In the
later phases of decomposition the presence of fauna had
a negative effect. In the total systems the fauna consistently increased the respiration rate. The loss of mass was
greater in the presence of fauna, especially during the
middle phases (5-11 months), but it was higher in the
controls later.
Throughout the whole incubation period the decomposition rate was strongly influenced by the composition
of the animal community. The interpretation of the resuits is affected by the fact that the controls, to which no
fauna had been added, contained dense populations of
microbial feeders (nematodes, rotifers, and protozoans).
Key words: Soil fauna - Decomposition - Raw humus
- Forest soil - Microcosm
-
CO
2
evolution
The soil fauna contributes significantly to the decomposition of dead organic matter, even though in most eco-
Offprint requests to: V. Huhta
systems the fauna is directly responsible for only a few
per cent of the decomposer respiratory metabolism
(Persson et al. 1980). This has been demonstrated in the
field by the traditional litter-bag method (Edwards and
Heath 1963; Seastedt et al. 1983), in combination with selective biocides (Vossbrinck et al. 1979; Seastedt and
Crossley 1980), and in the laboratory (Hanlon and Anderson 1979; Bengtsson et al. 1988; Set~il/i et al. 1988).
In most cases experiments with litter-bags have failed
to show whether the material lost from the bags had actually been decomposed, or had merely been transported
out of the bags by the fauna. Witkamp and Olson (1963)
suggested that the litter-bag method can only give approximate values for actual weight loss and losses of elements. In contrast, laboratory experiments (in which the
element fluxes can be monitored accurately), can be criticized for oversimplification of both biotic and abiotic
factors (Anderson 1978).
Decomposition of organic matter is regulated by interactions between the substrate quality, the biota, and
the microclimate (Swift et al. 1979). Mutual relationships
among the biota, especially between the microflora and
their invertebrate grazers, has also been reported to be extremely important in affecting the degradation processes
(reviewed by Anderson and Ineson 1984; Coleman et al.
1984). In addition, rates of decomposition may be influenced by interspecific relationships within the faunal
component (Kajak and Jakubczyk 1977; Santos and
Whitford 1981; Set~tl~i et al. 1990a).
Thus, to simulate natural decomposition processes in
controlled laboratory conditions, interactions between
biotic and abiotic environments, as well as connections
among the decomposer organisms, should be taken into
account. Our aim was to conduct a long-term laboratory
experiment with a structurally complex substrate in order
to study the role of the fauna in the decomposition processes of coniferous forest soil. Special emphasis was put
on the rate of decomposition in systems with different
faunal communities. Results of the present paper are obtained from the experiments described in detail by Huhta
and Set/il~i (1990).
164
Materials and methods
The experiments were carried out in plastic boxes ( 4 0 × 6 0 c m ; depth
12 cm) in which a simulated coniferous forest floor was created. Leaf
litter of silver birch (Betulapendula), needle litter of Norway spruce
(Picea abies), and raw h u m u s were used as test materials. These were
placed in nylon-mesh baskets in a systematic m a n n e r and inserted into
the substrate h u m u s . The boxes with their contents are termed "macrocosms", and the m e s h baskets containing the actual test materials are
"microcosms". A constant flow of air (30 liters h -1) was maintained
through the boxes. The boxes were incubated in darkness at + 16 ° + 1 °C
except during artificial winters, when the temperature was lowered stepwise (5 °C weekly) to + 1 ° _+1 °C. Three separate experiments were conducted; those with organic matter only are defined as experiments IA
a n d IB, and that with organic + mineral matter as experiment II.
A detailed description of the experimental design a n d procedures is
presented by H u h t a and Set/ila (1990).
The evolution of CO 2 from the macrocosms was measured from the
outgoing air using an infrared C analyzer (URAS 7N). The analyzer was
connected to a microcomputer, programmed to take repeated measurements for 15 m i n and then to change the unit to be measured by giving
a signal to a magnetic valve system.
To measure the respiration of the test materials separately, microcosms were moved into 0.5-liter glass jars equipped with air-tight lids.
During incubation in a climate chamber, a hole in the lid was closed
with a rubber septum. One 5-ml subsample was taken from the air space
with an injection needle at the m o m e n t the lid was closed, and another
after 60 min of incubation. The sample was injected into the analyzer,
and CO 2 production was calculated from the difference between the recordings. After the m e a s u r e m e n t h a d been taken, each microcosm was
returned to its original position in the macrocosm.
In experiment IA, six replicate microcosms of each test material
were measured (three each taken from two macrocosms). In experiments
IB and II, five replicates of each material were analyzed at a time; in
successive measurements they were taken alternatively from two macrocosms until the first destructive sampling, after which only one macrocosm per treatment remained. The units used were the same for all measurements taken during one season.
The cumulative evolution of CO 2 from both the microcosms and
the macrocosms was estimated from successive m e a n values, assuming
a linear change between measurements. F r o m the data on the macrocosm winter respiration (not shown), it was a s s u m e d that the evolution
of CO 2 during the winter periods was ca. 1/6 of that measured in the
s u m m e r periods.
The estimates of faunal respiration were based on the relationships
between body weight and 0 2 c o n s u m p t i o n as given in the literature and
converted to CO 2 production. Data for 02 c o n s u m p t i o n were obtained
from Persson et al. (1980); calculation of the faunal biomass is described in H u h t a and Set/ala (1990).
At intervals of 4 - 6 weeks (excluding the winters) the microcosms
were removed from the macrocosms, a n d irrigated with distilled and deionized water for the analyses o f total C. At the same time the macrocosms without microcosms were watered. The total C in the leachates
was determined with the C analyzer after 50-~tl subsamples were burned
at + 9 5 0 ° C .
A detailed description of the irrigation procedure is presented by
Set~il~ et al. (1990b).
At the end of each s u m m e r season a destructive sampling was carried out using some of the macrocosms. In experiment IA two refaunated and two control macrocosms were sampled after the first season. In experiments IB and II half the units were sampled after the first
season, and the rest after the second season. At each destructive sampling, 10 (experiment IA) or 5 (experiments IB and II) microcosms of
each test material were randomly chosen for determinations of the loss
in mass. The samples in the microcosms were carefully removed and
placed for 7 days in a high-gradient extractor to extract microarthropods, and then weighed after keeping at + 80 °C for 24 h.
During weeks 2 3 - 2 4 and 4 3 - 4 4 the total a m o u n t of h u m i c substances (humic acids and fulvic acids, excluding humines) in the
leachates from the whole macrocosms were analyzed by high-performance liquid chromatography (Knuutinen et al. 1988). The results are
expressed as relative units because there was no reference liquid for the
soil water.
Statistical differences over long intervals were tested by analysis of
variance for repeated measurements. Differences between particular
samplings were tested by analysis of variance or Student's t-test (Huhta
and Set~il~i 1990).
Results
Respiration
There was a significant difference (P< 0.05) in the respiration rate (calculated per unit mass) between the test materials during the whole incubation period (Table 1). For
all treatments and materials there was a trend towards a
lower respiration with time (spruce litter in experiment IA
formed an exception). After each winter period, however,
the amount of CO2 evolved generally increased. The enhanced respiration rates generally took ca. 10 weeks until
a new balance at a lower level was achieved (Fig. l d - g , i).
In the birch litter the respiration was significantly
stimulated in the refaunated units, especially during the
early phases of incubation (experiment IA; Fig. 1 a; Table
1). The same trend continued until the second winter
(week 56) in experiment IB and even longer in experiment
II (Fig. 1 d, e; cumulative values in Table 1). During the
late phases, respiration was generally lower in the refaunated units, although the difference between the controis and the refaunated systems was statistically signifi-
Table 1. Estimated cumulative evolution of C O 2 (mg C g - ~ dry matter) in microcosms containing birch and spruce litter at the time of the final
destructive samplings
Weeks 0 - 1 8
Weeks 0 - 4 7 / 4 8
Birch
Experiment IA
Experiment IB
Experiment II
Spruce
F
C
107 **
.
.
.
.
75
.
.
.
.
Birch
F
C
F
57 ***
42
.
123 **
144"
Weeks 0 - 9 7 / 9 8
Spruce
.
C
F
.
94
111
.
88
68
Birch
C
.
F
.
78
71
.
200
219
Spruce
C
F
C
.
178
176
131
116
125
131
F, refaunated (macrocosms with complex faunal assemblage); C, control (with microbes and microfauna only). * P < 0 . 0 5 , * * P < 0 . 0 1 , * * * P < 0 . 0 0 1 ,
versus control
165
pg.
IA
-1. h-1
IA SPRUCE
BIRCH
***
200.
100-
30-
150.
75-
25"
100-
50'
50,
25"
Z
6
i, ,"l'/°-O'•/§
®
/~HUMUS
IA
2015-
½
8 1'0 1'2 1'4 I'6 1'8
i
g
8
I'0
1'2 1'4 1'6 1'8
Weeks
120"
IB
(~)
100-
BIRCH
100
80-
80-
60-
60
40-
40,
20-
20w
w
g' "2'0
6°1
3'0
t
4'0
sb
II BIRCH
l
t
" f5
8's
9'5
I B sPRucE
60-
W
"2'0
W
3'0
4'0
~@
5'0
80
90 Weeks
8'0
9'0-~ w e ek s
II SPRUCE
40-
20201
,W
,
5
~ e
2"0
3b
4b
IA
W
/
5b
f5
8'5
9'5
z
TOTA L
.÷*-;
A
\;~U"
w
3'0
4 '0
IB+II
40-
®
. ,\j~/T',
w
"~20
5'0
TOTAL
30-
20
20. ÷-t
10
&
6
~
1'0
1'2
1'4
16
18
2b
2'2
Fig. L Instantaneous evolution of CO 2 (pg g-1 dry matter h -1,
means+ SE) from the microcosms (birch, spruce, humus) and macrocosms (total) in three experiments; • - - • , refaunated; O - - 0 , con-
t
W
,/
5 "2'0
2'5
3'0
W
--r/ . ~
35 75
8'0
9'5
9'0 Weeks
trol; asterisks show either significant differences for the whole experiment (at the end of each diagram) or the previous growing period (analysis of variance for repeated measurements); W,, artificial winter
166
cant only in experiment IB (P = 0.009 from week 56 onwards).
A similar pattern between the refaunated and control
units was observed in the spruce litter. From week 1 to 18
(experiment IA) the refaunated microcosms respired significantly more than the controls (Fig. 1 b; Table 1). During the middle phases of incubation there were some differences in respiration between experiments IB and II. In
the former the refaunated spruce litter continued to respire more than the controls, whereas in experiment II the
opposite was true. During the late phase (from the second
winter onwards) in both experiments the amount of CO2
produced was generally greater in the control units
(Fig. 1 f, g; Table 1).
In cOntrast to the litter materials in experiment IA,
respiration activity in the humus was generally higher in
the control microcosms. From week 6 to 18 respiration
measured in the control microcosms was significantly enhanced (P< 0.05 in four recordings out of seven) over the
level in the refaunated units (Fig. 1 c).
Although the effect of the fauna on CO2 evolution
was negative in the microcosms containing humus, it exerted a positive influence on the respiration measured
from whole macrocosms (experiment IA; Fig. 1 h). During 22 weeks' incubation the mean cumulative respiration
was 83.7 g CO2 in the refaunated systems, and 80.3 g in
the controls. The difference was statistically significant
(P = 0.003).
During the middle and late phases of incubation (experiments IB and II) the respiration level remained slightly higher in the refaunated macrocosms than in the controis, although no statistical differences were found
(Fig. 1 i). The cumulative sums of CO 2 produced from
the whole systems during the 97-98 weeks' incubation
were 260 g vs 239 g, and 263 g vs 245 g COz for experiments IB and II (refaunated vs control), respectively.
The contribution of faunal metabolism (estimated at
the time of the samplings) to the total respiration was
more pronounced in the refaunated systems than in the
control systems (Table 2). The most marked faunal contribution was generally a result of the large enchytraeid
Table 2. Estimated total and faunal respiration (Ixg CO2-C g-1 dry
matter h-1) in refaunated and control microcosms with birch and
spruce litter from destructive samplings of experiments IB and II
Refaunated
Birch
Control
Spruce
Birch
Spruce
IB
II
IB
II
IB
II
IB
II
Weeks 47 - 48
Total
Faunal
Faunal (%)
12.9
1.2
9.3
13.1
1.7
12.9
5.9
0.4
6.8
6.8
0.4
5.9
7.6
0.4
5.3
9.8
0.7
7.1
5.5
0.1
1.8
6.9
0.4
5.8
Weeks 97 - 98
Total
Faunal
Faunal (%)
5.5
1.4
25.4
9.3
0.2
2.2
5.2
0.4
7.7
5.7
0.1
1.8
7.6
0.4
5.3
9.3
0.1
0.5
5.7
0.1
1.8
6.6
0.1
1.5
See footnotes to Table 1
Table 3. Cumulative leaching of total C (mg C'microcosm -~) from
microcosms containing birch litter, spruce litter or humus by the end
of destructive samplings
Expt IA
Week 18
Birch
Spruce
Humus
Weeks 47 - 48
Birch
Spruce
Expt IB
F
C
9.6*
15.6
20.4
6.4
17.9
18.6
m
Weeks 97 - 98
Birch
Spruce
F
Expt II
C
F
C
m
m
16.0"
30.6*
26.4
22.2
9.3
27.3
18.4
30.8
23.7
41.2"
33.7
32.3
15.0
37.2
25.3
36.0
Expt, experiment; for other explanations, see footnotes to Table I
populations. In experiment IA, where the populations
were still developing during week 18, the animals did not
account for more than 1.5°70 of the total.
In the total macrocosms the proportion of the total
CO2 production contributed by the fauna was estimated
to be ca. 5O/o in weeks 47-48 and 10% in weeks 97-98.
The microbivorous fauna including nematodes and
rotifers (protozoans not estimated; see Discussion) present in the control macrocosms was estimated to produce
less than 5°70 of the total CO2.
Leaching of C
During the first 18 weeks of incubation, all recordings
showed significantly more total C leached from the refaunated birch litter than from the controls (experiment
1 A; Table 3). However, the leaching from the spruce litter
was generally more pronounced in the controls. C leaching from humus was significantly (P< 0.05) enhanced in
the refaunated units at the two first waterings (weeks 3
and 7), but from week 10 onwards less C leaching took
place in the refaunated units; in two measurements out of
three the release of total C was significantly greater
(P