FEMS MicrobiologyEcology53 (1988) 133-140
Published by Elsevier
133
FEC 00158
Seasonal population changes of myxomycetes
and associated organisms in four woodland soils
A. F e e s t a n d M . F . M a d e l i n
Department of Botany, University of Bristol, Bristol, U.K.
Received 29 July 1986
Revision received9 November 1987
Accepted 17 November 1987
Key words: Slime mould; Myxogastrid; Phagotroph; Dictyostelid; Ciliate; Amoeba; Bacterium
1. SUMMARY
2. I N T R O D U C T I O N
The number of myxomycete plasmodium-forming units (PFUs) and associated microorganisms
in soils from four woodland sites in the West of
England were estimated at approximately monthly
intervals over the course of a year, and other
characteristics of the soils were determined. The
numbers of PFUs were low except in an unusual
high-phosphate woodland soil. This soil contained
the fewest dictyostelid slime moulds. Conversely,
the woodland soil with most dictyostelids contained the fewest PFUs. Naked soil amoebae were
the most abundant phagotrophs. Myxomycetes
were a comparatively small component of the
phagotrophic community of the three typical
woodland soils. Changes in the populations of
naked amoebae, ciliates, myxomycetes and dictyostelids were sometimes synchronized with
changes in the bacterial populations, which showed
9-35-fold seasonal variations in abundance at the
four sites.
Published quantitative data on the abundance
of myxomycetes in soils describe the numbers of
plasmodium-forming units (PFUs) in samples of
soil collected world-wide as well as from many
natural sites in the West of England [1-4]. In this
paper we present data on myxomycete numbers in
soils from four woodland sites in the county of
Avon in the West of England which were sampled
once a month for at least a year, thus giving a
picture of the population dynamics of these
organisms. We also present data on associated
microbiological, chemical and physical characteristics of the soils and attempt to interpret the
population changes.
Correspondence to: M.F. Madelin, Department of Botany, University of Bristol, Woodland Road, Bristol BS8 lUG, U.K.
3. M E T H O D S
Methods of sample collection, enumeration of
organisms, and physical and chemical analyses of
the soils were as described by Feest and Madelin
[1,2]. Numbers of soil bacteria other than myxobacteria were determined by dilution plating and
expressed as g-1 fresh weight of soil. The sizes of
all other populations were determined by the
0168-6496/88/$03.50 © 1988 Federation of European MicrobiologicalSocieties
134
most-probable-number method [1] and expressed
as numbers cm -3 of fresh soil. Because myxomycete and dictyostelid amoebae were not readily
distinguishable from other naked amoebae they
would also have been included in the latter estimate. Successive samples at each site from the end
of 1981 or beginning of 1982 were taken within a
permanent 1 m 2 quadrat. The quadrat was divided
into 100 numbered 10 cm squares, and single
cylindrical cores of 1 cm 2 cross-sectional area were
removed from the upper 4 cm of the soil profile in
60 of them chosen by r a n d o m numbers, and thoroughly mixed. Different sets of random numbers
were used at successive samplings. Sample weight
is a measure of soil density and was expressed as
fresh weight (g) of 50 cm 3 of soil. Moisture content
was expressed as a percentage of the fresh weight
of the soil. Mineral concentrations were expressed
as parts per million by weight in dry soil.
Meteorological data were provided b y the Long
Ashton Research Station weather-recording centre
which was within 12 km of the farthest site. The
woodland sites examined and their Ordnance
Survey grid references were as follows.
3.1. Chew Valley Lake: Alnus plantation (0. S. No.
S T 566583)
This was a plantation of alder (Alnus glutinosa)
on a waterlogged alluvial soil bordering a reservoir. The grove of trees was neglected and
natural thinning was occurring, surviving trees
being about 8-10 m high. A shaded ground flora
indicated nitrogen enrichment in that Urtica dioica
was present. The ground cover was 70% of which
40% was of Urtica dioica, Rubus sp. and
Ranunculus repens, and the rest Poa nemoralis.
The soil was a waterlogged (gleyed) silty loam, but
during draw-down of the reservoir the water-table
dropped by m a n y centimetres. At times in past
years, especially during spring, the site had been
inundated by a few centimetres of water, but this
did not happen in the year of study.
3.2. Long Ashton: High-phosphate woodland (O.S.
No. S T 565697)
This was chosen as a contrast to the other
woods where phosphate was of limited availability
(Table 3). The soil was a black loam with a good
crumb texture. G r o u n d cover was sparse because
of heavy shading from a large specimen of Acer
campestris and some r a m p a n t growth of Clematis
vitalba. Fraxinus excelsior and Acer pseudoplatanus were the other dominant trees around the
site. Cover was 25% of which Hedera helix contributed 10%, Urtica dioica 4%, Glechoma hederacea
4%, Rubus sp. 5% and Allium ursinum 1%, together with a few stems of Poa nemoralis.
3.3. Leigh Woods: Fagus woodland (O.S. No. S T
556734)
This was a level site under mature beech trees
(Fagus sylvatica) greater than 15 m high. The top
1.5 cm of the soil profile consisted of decomposing
beech leaves and overlay a stiff clayey brown-earth
soil. The 10% ground cover was of suppressed
Rubus sp. and Crataegus monogyna with numerous Fraxinus excelsior seedlings.
3.4. Leigh Woods: Mixed species woodland (O.S.
No. S T 555733)
This was a level site under mature Quercus sp.,
Acer pseudoplatanus, Fraxinus excelsior, Taxus
baccata and Betula pubescens. The 10% ground
cover was of Rubus sp. and seedlings of Fraxinus
excelsior and Acerpseudoplatanus. During the year
of sampling an adjacent Acer pseudoplatanus tree
was felled and caused some soil disturbance on
the plot. The top 2 cm of the soil profile was of
decomposing leaf material and overlaid a clayey
brown-earth soil.
4. R E S U L T S A N D D I S C U S S I O N
4.1. Weather
Table 1 presents the seven-day means for three
measurements of weather (viz., surface minimum
temperature, soil temperature at 10 cm depth and
rainfall) immediately prior to each date of sampiing. The sampling period included some weather
which was extreme by the usual standards for the
West of England. There was a severe winter frost
(December and January), a spring drought (April
and May), and a summer drought (July). This was
135
Table 1
Seven-day means of data for weather immediately prior to each
date of sampling
Date
06.10.81
16.10.81
11.11.81
21.12.81
19.01.82
15.02.82
15.03.82
14.04.82
14.05.82
20.06.82
25.07.82
26.08.82
30.09.82
14.10.82
14.11.82
13.12.82
Grass minimum
temperature
Soil temperature
at 10 cm depth
(o c)
( ° c)
4.7
5.6
-1.5
- 6.0
- 6.4
1.9
1.8
- 1.5
2.1
7.2
10.8
7.2
5.2
5.3
5.6
- 1.1
12.7
8.4
5.7
0.6
1.2
5.9
5.3
6.8
11.1
16.0
19.3
14.9
11.9
10.8
9.6
4.6
Rainfall
(ram)
4.3
3.4
0.1
4.3
0.4
3.5
9.3
0
0
6.1
0
4.2
7.5
4.9
7.7
8.5
followed by a warm moist autumn (August to
November).
4.2. Biological and other characteristics of the four
soils
4.2.1. Chew Valley Lake: Alnus plantation (Tab& 2). PFUs were recorded in ten of the twelve
successive samples during the year, and dictyostelids from nine. This site yielded mean and maximum numbers of PFUs which were below 1% of
those of naked amoebae. The mean number of
dictyostelids was raised above that for PFUs by
one particularly high value (500) in September,
but otherwise the numbers were broadly similar.
Soil organic matter (expressed as percentage loss
on ignition) was low, probably because of rapid
decomposition associated with the relatively large
bacterial populations (cf. the soils from the two
Leigh Woods sites, Tables 4 and 5).
Changes in the biological parameters have
proved difficult to interpret. Numbers of bacteria
were low in the cold early part of the year when
the soil was saturated, but the warming and drying of the soil from about April onwards were
associated with increases. Changes in the populations of PFUs, total naked amoebae and ciliates
were virtually unsynchronized during winter and
spring but synchrony of changes evolved after
May. The population of PFUs reached a midwinter peak of 170 cm -~ at the time of severe
frost (December), fell during spring, but showed
minor peaks during summer. There were three
occasions in autumn and winter when ciliates outnumbered amoebae and represented the dominant
soil protozoan biomass. The variation that occurred in the concentrations of minerals in this
and the other soils studied probably reflects the
variable nature of the top 4 cm of the soil profile.
4.2.2. Long Ashton: High-phosphate woodland
(Table 3). The sampling period for this site
(January to December) was a little later than for
the other sites (October to September). The soil
was phosphate-rich but nitrogen-poor; p H and
calcium levels were high for a woodland soil. Of
the four woodland soils studied, this one showed
the highest mean and maximum numbers of PFUs,
amoebae, ciliates, myxobacteria, and bacteria, and
the lowest mean and maximum numbers of dictyostelids as well as the smallest number of positive monthly records. A steep transient rise in
numbers of PFUs in February and March after
the winter frost coincided with a similar rise in
naked-amoebal numbers and a fall in bacterial
numbers as if the phagotrophic organisms were at
least partly responsible for the latter fall. The
mean number of PFUs throughout the year was
about one tenth of the mean number of soil
amoebae. All the measured populations tended to
decline from April onwards, coincident with the
soil drying, but rewetting of the soil after July was
not accompanied by sustained increases. From
May to December when all the populations were
relatively small there was close synchrony of the
changes in numbers of PFUs and bacteria (r =
0.95, P = < 0.1%).
4.2.3. Leigh Woods: Fagus woodland (Table 4).
Unlike the soils from the preceding two sites, this
one was rich in organic matter (expressed as percentage loss on ignition), and related to this had a
higher moisture content. The p H was lower and
nitrogen content higher than in the previous two
sites. Myxomycetes were present (Table 4) but
were few in number. PFUs were detected on only
three out of twelve occasions throughout the year,
136
Table 2
The abundance of myxomycete PFUs and associated organisms in soil from an Alnus glutinosa plantation at Chew Valley Lake, and
the chemical and physical characteristics of the soil, determined at approximately monthly intervals throughout one year
(a) Numbers of microorganisms cm-3 ,
Date
PFUs
Amoebae
Dictyostelids
Ciliates
Nematodes
Myxobacteria
Bacteria
(millions) *
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
20 Jun
25 Jul
26 Aug
19 Sep
20
0
170
50
70
20
20
0
90
20
80
50
110
400
5 500
140
2500
16000
> 18000
9000
9 000
2750
9000
3 500
0
0
80
40
90
20
80
40
20
0
60
500
130
800
200
350
650
500
500
140
200
110
500
250
20
20
50
20
50
0
0
0
20
0
0
0
1 300
110
800
130
1100
130
1100
500
200
1 300
80
110
27
6.5
3.5
3.9
2.5
6.0
15
88
19
21
31
14
49
> 6 325
78
361
15
572
Mean
20
(b) Chemical and physical characteristics
Date
Sample
weight
(g)
Water
content
(% fresh
wt.)
% loss on
ignition
pH
Ca
(ppm)
Mg
(ppm)
K
(ppm)
Na
(ppm)
NH 4 •N
(ppm)
PO 4
(ppm)
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
20 Jun
25 Jul
26 Aug
19 Sep
46.0
50.7
42.4
63.3
48.6
44.8
58.6
51.2
34.0
47.2
44.6
43.4
35.5
38.1
42.3
45.8
40.2
43.1
40.8
27.0
35.6
30.8
32.6
21.0
11.0
14.1
13.5
12.9
10.9
13.1
12.8
9.9
10.9
11.8
12.2
12.8
5.1
4.7
5.1
5.0
4.8
4.8
5.0
4.7
4.4
4.5
4.5
5.1
1658
1550
1 349
1 289
1317
1133
1705
1616
1637
1537
2 830
1870
197
258
232
214
199
198
284
251
226
221
161
151
70
124
134
98
79
84
187
151
161
125
103
95
62
65
89
52
53
229
109
83
114
91
29
27
35
35
45
32
69
60
46
76
80
112
71
53
16
9
5
6
12
19
6
19
42
21
12
7
Mean
47.9
36.1
12.2
4.8
1624
216
118
89
60
14
* Bacteria expressed, g - x fresh weight.
while dictyostelids were detected on eight. Bacteria
were at only about one fifth of their abundance in
t h e p r e v i o u s t w o w o o d l a n d sites. T h e r e w e r e p r o nounced positive correlations between seasonal
c h a n g e s o f soil m o i s t u r e c o n t e n t , b a c t e r i a l n u m bers and numbers of ciliates (for March to Sept e m b e r , r -- 0.955, P = < 0.1% f o r b a c t e r i a a n d
ciliates). W h e t h e r t h e c o r r e l a t i o n b e t w e e n t h e
numbers of bacteria and ciliates was direct or was
m e d i a t e d t h r o u g h soil m o i s t u r e is n o t e v i d e n t .
4.2.4. Leigh Woods: Mixed species woodland
(Table 5). T h e p o p u l a t i o n sizes a n d s e a s o n a l
c h a n g e s i n t h e soil a t t h i s site w e r e v e r y s i m i l a r t o
those at the nearby preceding one. The moisture
r e g i m e , h o w e v e r , s h o w e d less a b r u p t c h a n g e s , d r y i n g s t e a d i l y f r o m N o v e m b e r t h r o u g h till J u l y . A
wet period in August eventually reversed the trend.
M y x o m y c e t e s w e r e a g a i n f e w i n n u m b e r , t h i s site
showing the lowest mean and maximum numbers
among the four woodlands. PFUs were detected in
137
Table 3
The abundance of myxomycete PFUs and associated organisms in soil from a high-phosphate wood at Long Ashton, and the
chemical and physical characteristics of the soil, determined at approximately monthly intervals throughout one year
(a) Numbers of microorganisms c m - 3 .
Date
PFUs
Amoebae
Dictyostelids
Ciliates
Nematodes
Myxobacteria
Bacteria
(millions) *
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
14 Oct
15 Nov
13 Dec
500
1300
2 500
800
800
130
250
500
120
200
170
250
5 500
9000
> 18000
5500
9000
5 500
9000
3 500
1700
1100
5 500
2250
20
0
20
40
0
0
0
0
20
0
0
0
500
1100
500
1100
350
250
130
50
350
250
300
700
0
0
20
0
20
20
0
0
0
0
20
0
16 000
120
110
1100
1100
1100
950
140
850
1300
350
1 300
160
5.0
14
57
36
14
11
20
6.6
11
8.1
10
627
> 6 296
8
465
7
2 035
29
Mean
(b) Chemical and physical characteristics
Date
Sample
weight
(g)
Water
content
(% fresh
% loss on
ignition
pH
Ca
(ppm)
Mg
(ppm)
K
(ppm)
Na
(ppm)
NH4.N
(ppm)
PO4
(ppm)
wt.)
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
14 Oct
15 Nov
13 Dec
41.6
43.0
50.0
45.9
47.1
38.3
47.4
31.4
44.0
44.7
36.7
47.2
46.5
36.3
41,0
35.0
27.5
29.9
20.8
23.5
29.4
32.0
35.3
39.3
12.8
14.3
13.3
13.5
12.4
12.4
15.4
12.9
13.2
12.5
14.3
12.1
6.5
6.5
6.7
6.9
6.5
5.9
6.4
6.9
6.8
6.7
7.3
6.9
1414
2060
1802
1160
2 383
2701
2432
2700
1920
2270
2060
2980
117
198
174
128
233
262
228
144
92
96
108
150
216
414
264
215
334
356
279
170
182
233
281
304
20
34
34
133
78
58
59
33
33
51
28
28
38
27
45
19
66
45
30
30
30
30
15
27
62
54
65
113
72
85
70
70
65
60
62
124
Mean
43.1
33.0
13.3
6.7
2156
161
271
49
34
77
* Bacteria expressed, g - 1 fresh weight.
seven of the twelve soil samples but in only one
did their number exceed 20 cm -3, the minimum
detectable number. This higher value coincided
with the peak value in the nearby Fagus woodland
site, in October. In contrast, dictyostelids were
abundant, being detected in eleven of the twelve
samples, and reached a peak in July of 1100 c m - 3.
These values are of the same order as those found
by Kuserk [5] and Turner [6] and, with allowance
for differences in sampling technique, are similar
to those of Cavender [7]. There were two periods
when peaks in the numbers of dictyostelids coincided with troughs in the numbers of bacteria, and
steep falls in the numbers of dictyostelids coincided with steep rises in numbers of bacteria.
However, there was a period between, during
which these two populations were rather small, in
which changes in their numbers were synchronized
(December to May). The numbers of soil protozoa
showed a succession of peaks as the soil dried, a
138
Table 4
The abundance of myxomycete PFUs and associated organisms in soil from a Fagus syloatica woodland at Leigh Woods, and the
chemical and physical characteristics of the soil, determined at approximately monthly intervals throughout one year
(a) Numbers of microorganisms cm -3 *
Date
PFUs
Amoebae
Dictyostelids
Ciliates
Nematodes
Myxobacteria
Bacteria
(millions) *
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
250
0
20
0
0
0
0
0
0
0
20
0
5 500
170
250
3 500
2 750
5 500
1100
2 500
3 500
1300
3 500
500
0
0
140
40
0
40
40
20
70
0
40
20
200
20
110
50
80
20
350
500
80
0
200
130
0
0
0
0
0
20
0
0
0
0
0
0
1100
500
1200
50
250
140
50
5 500
50
50
110
2 250
4.1
5.9
1.1
1.6
0.66
1.7
5.9
11
3.4
1.2
5.8
4.9
24
2 506
145
2
93
Mean
31.
3.9
(b) Chemical and physical characteristics
Date
Sample
weight
(g)
Water
content
(% fresh
wt.)
% loss on
ignition
pH
Ca
(ppm)
Mg
(ppm)
K
(ppm)
Na
(ppm)
NH 4" N
(ppm)
PO 4
(ppm)
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
41.3
37.7
47.9
59.1
56.3
36.8
47.1
35.1
40.1
39.0
34.8
35.3
51.6
51.3
45.1
59.2
41.0
47.8
55.6
55.3
45.9
51.6
51.1
43.4
28.0
30.7
35.0
30.6
29.0
28.1
29.8
30.2
29.3
36.5
25.2
20.3
4.1
4.1
4.0
3.8
3.9
3.8
4.0
3.9
3.6
3.6
3.7
4.0
1788
1689
1385
983
811
693
722
1236
1505
1211
1286
1710
258
248
232
177
120
151
168
202
269
204
205
99
210
233
217
148
88
106
144
179
233
151
158
120
44
70
54
33
36
30
36
81
86
67
86
51
120
74
95
80
114
103
110
65
140
80
100
55
6
7
8
12
19
9
9
23
27
25
10
13
Mean
42.5
49.9
29.4
3.9
1252
194
166
56
95
14
* Bacteria expressed.g i fresh weight.
ciliate peak (April) being followed by an amoebal
one (May, June) and then a dictyostelid one (July).
Rain in August was accompanied by an increase
i n all p o p u l a t i o n s e x c e p t d i c t y o s t e l i d s .
5. G E N E R A L
DISCUSSION
W h i l e t h r e e o f t h e w o o d l a n d soils w e r e a l i k e i n
containing only small mean and maximum numbers of PFUs (respectively 16-49 cm -3 and
7 0 - 2 5 0 c m - 3 ) , t h e soil f r o m t h e L o n g A s h t o n
high-phosphate woodland was exceptional in containing many (mean 627 cm -3, maximum 2500
cm-3). It was also the richest in bacteria (includi n g m y x o b a c t e r i a ) a n d c i l i a t e s ( T a b l e 3). T h e f i n d ing that myxomycete PFUs were few in the typical
w o o d l a n d s o i l s is i n a c c o r d w i t h t h e r e s u l t s o f
F e e s t a n d M a d e l i n [1,2] a n d F e e s t [3]. T h i s p a u c ity does not conflict with fidd observations that
myxomycetes appear common in woodlands, for
139
Table 5
The abundance of myxomycete PFUs and associated organisms in soil from a mixed woodland at Leigh Woods, and the chemical
and physical characteristics of the soil, determined at approximately monthly intervals throughout the year
(a) Numbers of microorganisms c m - 3 ,
Date
PFUs
Amoebae
Dictyostelids "
Ciliates
Nematodes
Myxobacteria
Bacteria
(millions) *
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
70
0
20
20
20
20
0
0
0
0
20
20
800
200
200
400
350
1700
2 000
9000
9000
3 500
5 500
3 500
500
170
80
110
0
20
70
140
50
1100
20
170
250
40
110
50
80
80
350
170
170
50
350
250
20
0
0
0
0
20
0
20
0
0
20
20
3 500
20
500
170
120
170
700
3 500
5 500
50
110
700
2.0
5.0
1.3
2.6
1.3
1.8
1.3
3.9
3.8
2.0
12.0
1.8
Mean
16
3 013
203
163
8
1253
2.3
(b) Chemical and physical characteristics
Date
Sample
weight
(g)
Water
content
(% fresh
wt.)
% loss on
ignition
pH
Ca
(ppm)
Mg
(ppm)
K
(ppm)
Na
(ppm)
NH 4 •N
(ppm)
PO4
(ppm)
16 Oct
11 Nov
21 Dec
19 Jan
15 Feb
15 Mar
14 Apr
14 May
21 Jun
26 Jul
26 Aug
30 Sep
44.6
44.5
54.7
69.1
34.6
50.9
48.0
43.8
40.7
33.6
34.9
40.0
47.7
53.9
50.6
48.4
41.0
42.1
40.5
39.1
37.7
34.4
47.8
41.1
13.6
22.8
22.4
17.6
18.2
22.4
18.1
22.2
17.2
23.1
21.9
30.9
4.8
4.0
3.9
4.0
3.8
3.8
4.1
3.9
3.8
3.9
4.1
3.8
738
965
825
685
1213
597
623
1053
743
1 256
1664
1180
105
130
147
114
235
82
125
160
129
154
187
103
86
129
136
81
210
73
85
152
141
156
184
118
28
27
43
27
52
51
26
86
57
80
83
52
103
76
80
95
116
91
83
55
125
80
99
55
19
7
10
10
12
8
6
10
21
15
5
8
Mean
45.0
43.7
20.8
4.0
962
139
129
51
88
11
* Bacteria expressed, g - 1 fresh weight.
s u c h o b s e r v a t i o n s a l m o s t i n v a r i a b l y p e r t a i n to
myxomycetes fructifying on rotting litter and wood
r a t h e r t h a n l i v i n g w i t h i n t h e soil. T h e h i g h - p h o s p h a t e soil w a s e x c e p t i o n a l in r e s p e c t o f its n o n b i o l o g i c a l c h a r a c t e r i s t i c s also. It c o n t a i n e d m o r e
t h a n five t i m e s as m u c h p h o s p h a t e as the o t h e r
t h r e e soils, w a s h i g h in c a l c i u m a n d p o t a s s i u m ,
a n d h a d a h i g h e r p H ( T a b l e 3b). R i c h in
m y x o m y c e t e P F U s , it was t h e p o o r e s t i n d i c t y o s t e l i d s ( m e a n 8 c m - 3 , m a x i m u m 40 c m - 3 ) .
C o n v e r s e l y , t h e soil w i t h t h e g r e a t e s t d e n s i t y o f
d i c t y o s t e l i d s ( L e i g h W o o d s m i x e d species w o o d l a n d ; m e a n 203 c m -3, m a x i m u m 1100 c m - 3 ) w a s
t h e o n e w i t h f e w e s t m y x o m y c e t e P F U s ( m e a n 16
c m -3, m a x i m u m 70 c m - 3 ) . T h e r e w a s t h u s a n
indication of an inverse relationship between
myxomycetes and dictyostelids when one or the
other achieved high population density.
Since there was a 9-35-fold seasonal variation
i n b a c t e r i a l n u m b e r s at t h e f o u r sites, the q u a n t i -
140
ties of nutrients moving in and out of the bacterial
pool must have been large and likely to affect
plant nutrition. This could be i m p o r t a n t in wood°
lands where the a m o u n t s of available nutrients are
generally small. At each of the four sites there was
evidence that p h a g o t r o p h i c populations played a
role in causing such fluctuations in bacterial n u m bers. Myxomycetes were sometimes a major comp o n e n t of these phagotrophic populations. The
enumerated P F U s were p r o b a b l y uninucleate
stages of the life cycle [2]. E n u m e r a t i o n of
m y x o m y c e t e s as P F U s almost certainly underestimated the n u m b e r of such cells because of
heterothallism as well as the possibility that some
species might not produce plasmodia in the conditions in the enumeration plates [1]. Consequently,
m y x o m y c e t e cells p r o b a b l y represented at least
15% of the population of a m o e b a e i n the L o n g
A s h t o n high-phosphate w o o d l a n d soil at various
times (Table 3). O n the other hand, they appeared
to represent only a small part of the p h a g o t r o p h i c
population in the other w o o d l a n d sites where, for
m u c h of the time, they were of the order of 1% of
the total, and sometimes were very m u c h less
(Tables 2, 4 and 5).
As was found in our studies of other soils [1]
the majority of myxomycetes which fructified in
e n u m e r a t i o n plates were Didymium species,
n a m e l y Didymium difforme, Didymium squamulosum and members of the long-stemmed Didymium
group described b y N a n n e n g a - B r e m e k a m p [8].
ACKNOWLEDGEMENTS
A.F. was supported b y a Science and Engineering Research Council studentship. The assistance
of a grant to M.F.M. f r o m the N a t u r a l Environm e n t Research Council to study the ecology of
soil m y x o m y c e t e s is gratefully acknowledged. W e
thank L o n g A s h t o n Research Station weather-recording centre for kindly furnishing the data for
Table 1. W e thank Dr. S.M. Ross of the Geograp h y Department, University of Bristol for assistance with chemical analysis of soils.
REFERENCES
[1] Feest, A. and Madelin, M.F. (1985) A method for the
enumeration of myxomycetes in soils and its application to
a wide range of soils. FEMS Microbiol. Ecol. 31, 103-109.
[2] Feest, A. and Madelin, M.F. (1985) Numerical abundance
of myxomycetes (myxogastrids) in soils in the West of
England, FEMS MicrobioL Ecol. 31, 353-360.
[3] Feest, A. (1986) Numbers of myxogastrids and other protozoa recovered from Bohemian soils. Ekolrgla ((~SSR) 5,
125-134.
[4] Murray, P.M., Feest, A. and Madelin, M.F. (1985) The
numbers of viable myxomycete cells in the alimentary
tracts of earthworms and in earthworm casts. Bot. J. Linn.
Soc. 91, 359-366.
[5] Kuserk, F.T. (1980) The relationship between cellular slime
moulds and bacteria in forest soils. Ecology, 61, 1474-1485.
[6] Turner, C. (1979) The ecology and identification of dictyostelid cellular slime moulds in South Western England,
Ph.D. Thesis, University of Bristol.
[7] Cavender, J.C. (1969) The occurrence and distribution of
Acrasieae in forest soils: 1. Europe, Am. J. Bot. 56, 989-992.
[8] Nannenga-Bremekamp, N.E. (1972) Notes on myxomycetes XVIII. A new Didymium and some comments on the
Didymium species with long-stalked sporangia, Proc. Kon.
Ned. Akad. Wetensch. Ser. C. 75, 352-363.