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Structure and development of fungal communities in beech logs four and a half years after felling
FEMS MicrobiologyEcology53 (1988) 59-70 Published by Elsevier
59
FEC 00149
Structure and development of fungal communities in beech logs four and a half years after felling I.H. C h a p e l a a, L y n n e B o d d y
a
and A.D.M. Rayner b
a Department of Microbiology, University College, Newport Road, Cardiff, and b School of Biological Sciences, Universityof Bath, Claverton Down, Bath, U.K.
Received 10 June 1987 Revision received4 September1987 Accepted 5 September 1987 Key words: Succession; Interspecific interaction; Replacement mechanism; Wood decay; Mycelial cord
1. SUMMARY The spatial structure of fungal communities which have developed, following colonization aerially and from the soil, in beech logs four and a half years after felling is described, and mechanisms for change are examined. Comparison with community structure at earlier samplings revealed a temporal change which was largely, but not completely, reflected by a hierarchy of combative ability. The most abundant species, both in terms of volume and number of logs occupied, were Xylaria hypoxylon, Coriolus versicolor and Armillaria bulbosa, all of which had persisted for a long time: after only six months the former two had occupied large volumes of wood, whilst A. bulbosa had begun to colonise subcortically. Some of the earliest colonisers, including Bjerkandera adusta and Chondrostereum purpureum, were not detected at the final sampling. Cord-forming fungi colonising from the soil were prevalent in basal regions after one year, and after four and a half years
Correspondence to: L. Boddy, Department of Microbiology, University College, Newport Road, Cardiff CF2 1TA, U.K.
were well established and evidently replaced a number of early colonisers. Several species which had not been found at earlier samplings were well established by the final sampling, These were Lenzites betulina, Psathyrella hydrophilum, Sistotrema brinkmanii and the Ascomycotina Lopadostoma turgidum. In addition, soil Deuteromycotina and mucoraceous fungi were present in some columns of well-decayed wood.
2. I N T R O D U C T I O N As decomposition of wood proceeds, the mycofloral composition and spatial structure of the communities change [1,2], but until recently most studies have been essentially floristic (e.g., Refs. 3-6), omitting important spatial considerations. Further, it is rare for mycofloral studies to be carried out in conjunction with those on decay rate, preventing assessment of the effect of community structure on decay. Neither is it usual for either type of study to extend for longer than 2 to 3 years - the typical length of a research award. Recently, however, Coates and Rayner [7-9] have described the spatial and temporal patterns of
0168-6496/88/$03.50 © 1988 Federation of European MicrobiologicalSocieties
60 establishment from aerially exposed and buried cut surfaces of beech logs over a 97-week period. These observations are extended in this paper where we describe community structure and state of decay, four and a half years after felling, and examine mechanisms for change.
3. MATERIALS A N D M E T H O D S
3.1. Site description and experimental design The experimental site was a stand of oak
(Quercus robur L.) with occasional beech (Fagus syloatica L.) in the Sallow Valets Inclosure, Forest of Dean, Gloucestershire (N.G. Ref. SO 611145). The stand had not been thinned prior to initiation of the experiment, but most beech trees were felled about 1 year before the final sampling, and the boles and brash were left in piles on the site. Details of soil and vegetation characteristics for an adjacent site are given elsewhere [10]. The experimental design is described in detail elsewhere [7]. Briefly, freshly felled beech logs (30-40 cm length, 10-20 cm diameter) were placed uptight, with their bases buried to a depth of approximately 10 cm, in March 1980. Some of these were allowed to be colonised naturally (series A), in others a slice 2 cm thick was removed from the upper surface at each sampling (series B), while a third group was treated with spore suspensions of wood-rotting Basidiomycotina (series C and D). Logs from each series were sampled on seven occasions during the first 129 weeks [7-9], and 50 remaining logs described in this paper were collected in November 1984, four and a half years after initial exposure.
3.2. Analysis of fungal communities The presence and distribution on the wood surface of recognisable macroscopic fungal structures, e]g., mycelium, cords and sporophores, were recorded. The orientation of geotropic structures indicated whether the position of the log had changed during the experiment due to large mammal activity or forestry operations. Each log was then sectioned on a band saw to reveal the three-dimensional patterns of decay. The high variation in state of decay of different logs made
standardization of the sectioning procedure impractical, but whenever possible transverse sections from the middle and both ends were made. The remainder of each log was then sectioned longitudinally. Patterns of decay, including zone lines and stained regions, were examined to identify the range of species involved, the most important columns (in terms of volume), and to reveal the probable origin of each. This was further aided by direct incubation of some sections in polythene bags at room temperature ( 1 8 - 2 0 ° C ) for up to 3 months, which allowed outgrowth of identifiable mycelium and occasionally fruit bodies. Selected individual decay columns were dissected from the logs. Samples were taken from these and volume, fresh weight and oven dry weight were measured to obtain estimates of density and water content. Fungal isolations were made by aseptically transferring small chips of wood on to plates of 2% (w/v) malt agar (MA), MA containing 10 ppm Novobiocin plus 50 ppm Benomyl, and MA acidified with lactic acid to approximately pH 3.5. These were incubated for up to 4 months, after which the resulting cultures were identified. When single decay columns exhibited variation in colour, texture or mechanical resistance isolations were made from throughout the decay column to ensure that differences in species composition were detected.
3.3. lnterspecific interactions Single isolates of 12 of the wood-rotting species were paired in all combinations, by placing 4-mm diameter inocula 3 cm apart on 9-cm plates of MA. Isolates of different species were inoculated at different times so that they met at the centre of the plate. Plates were incubated at 25 ° C, for up to 4 weeks under normal atmospheric conditions, and for up to 10 weeks under an atmosphere of 30% CO z, 5% 02. The latter gaseous combination was obtained in 3-1jars containing up to six plates and was renewed twice a week. 4. RESULTS
4.1. Species occurrence and state of decay The position of many of the logs was disturbed,
61
Ascomycotina were isolated, of which Xylaria hypoxylon, Armillaria bulbosa and Coriolus versicolor
partly as a result of forestry operations, and many of the tags identifying the original treatment were lost. For those which were identifiable, no difference in species composition was obvious, neither was it possible to detect a statistically significant difference (P < 0.05) in mean state of decay (g. cm-3). Untreated logs (series A) were slightly more decayed (0.29 + 0.4 g - c m -3) than series B and C logs (0.37 + 0.07 g. cm-3 and 0.36 _ 0.03 g. cm -3) but low sample numbers (5, 5 and 4, respectively) would make detection of differences unlikely. However, wood occupied by different species showed considerable differences in the amount of decay (see below), and overall density appears to be affected more by composition of the decomposer community at later stages than by initial treatment effects. Results for all logs are therefore treated together. Table 1 presents the frequency with which wood-rotting fungi were detected in all logs, combining results from isolation, direct incubation and presence of macroscopic fungal structures. Fourteen species of Basidiomycotina and eight
occurred most frequently, being found respectively in 90, 50 and 46% of logs. They also occupied the largest volumes of wood, although this was not quantified. In addition, five other Ascomycotina were found fruiting on the surface but were not isolated from the wood. These were Dasyscyphus virgineus (4% of logs), Diatrype disciformis (2% of logs), Lasiosphaeria spermoides and L. ovina (18% of logs) and Melanommapulvis-pyrius (6% of logs). The maximum number of species of higher fungi found in any log was seven with a modal value of four (Fig. 1). This was independent of the number of columns sampled in each log. Mucoraceous fungi and Deuteromycotina were isolated from most logs, and included species of
Acremonium, Cordana, Fusarium, Mucor, Paecilomyces, Penicillium, Phialophora, Torula, Trichoderma, Verticillium and sterile hyaline and dematiaceous fungi. Trichoderma spp. were very common, being found in over 90% of the logs. The state of decay (as represented by density)
Table 1 Frequency of occurrence of predominant fungi and state of decay of wood (density; g . c m - 3 ) in 50 logs, 51 m o n t h s after exposure, irrespective of treatment Coprinus spp. includes Coprinus micaceus and Ozonium sp. Fungus
Basidiomycotina
Ascomycotina
Frequency
Density ( g . c m - 3)
Coefficient of
Mean %
variation
weight loss
0.12-0.50 0.12-0.30 0.09-0.13
31.11 31.67 25.45
46.3 73.1 83.6
0.28+0.10 0.30+0.21 0.36_+0.12
0.22-0.38 0.18-0.51 0.28-0.46
26.07 51.33 24.17
58.2 55.2 46.3
3
0.14_+0.21
0.01-0.23
82.14
79.1
19 9 4 3
0.47+0.03 0.36_+0.07 0.415:0.12 0.20-+0.09
0.34-0.55 0.13-0.45 0.31-0.52 0.16-0.26
10.85 27.50 21.95 25.50
29.9 46.3 38.8 70.1
13
0.16-+0.03 0.67
0.08-0.23 0.65-0.70
26.88
76.1
No. of logs
% of logs
n
Armillaria bulbosa Coriolus versicolor Psathyrella hydrophilum Phanerochaete velutina Stereum hirsutum Phallus impudicus Tricholomopsis platyphylla Sistotrema brinkmanii Hypholoma fasciculare Coprinus spp. Lenzites betulina
25 23 13
50 46 26 18 12 10 10 8 6 4 4
Xylaria hypoxylon (pure)
45
90 28 14 8 90
9 6 5 5 4 3 2
2
(replaCed)
Hypoxylon sp. Lopadostoma turgidum Ascocoryne sarcoides Trichoderma spp. Uncoionised wood
14
7 4 45
+ 95% confidence interval
range
20 14 2
0.36+0.05 0.18 5:0.03 0.11+0.09
4 4 4
62 15 00 O
"6 10
d Z
2
3 NO.
4 of
6 apeole8
per
7 log
Fig. 1. Frequency distribution of number of species of Ascomycotina and Basidiomycotina forming decay columns in individual logs.
o f c o l u m n s o c c u p i e d b y d i f f e r e n t f u n g i fall i n t o t h r e e b r o a d c a t e g o r i e s ( T a b l e 1). F i r s t l y , t h o s e w h i c h w e r e r e l a t i v e l y little d e c a y e d ( a v e r a g e g r e a t e r t h a n 0.4 g - c m - 3 ; a n d w i t h l o w v a r i a t i o n ) u s u a l l y c o n t a i n e d t h e A s c o m y c o t i n a Xylaria hypoxylon o r Hypoxylon serpens. W h e n X. hypoxylon w a s replaced density decreased. The second category, with an average density of 0.3-0.4 g. cm-3, comprises the cord- and rhizomorph-forming fungi
Armillaria bulbosa,
Phallus impudicus and Tri-
Fig. 2. Longitudinal section through wood containing columns of Coriolus oersicolor (Cv) and Xylaria hypoxylon (Xh). The columns of X. hypoxylon are surrounded by pseudosclerotial plates (psp) which when cut allow water into formerly dry regions (w) occupied by X. hypoxylon. Scale bar represents 1 cm.
cholomopsis platyphylla. T h e t h i r d c a t e g o r y , w i t h a n a v e r a g e d e n s i t y o f less t h a n 0.3 g - c m -3, c o m p r i s e s Coriolus versicolor, Hypholoma fasciculare, Psathyrella hydrophilum, Stereum hirsutum a n d the
Fig. 3. ('a) Transverse section from near the base of a log after direct incubation in an humid atmosphere. Xylaria hypoxylon (Xh) is present in peripheral regions although, as indicated by the presence of relic zone lines (rzl), formerly it occupied almost the entire section. Tricholomopsisplatyphylla (Tp) now occupies the majority of the central regions of the section and its mycelium has grown out of the wood in certain places. (b) Longitudinal section showing X. hypoxylon confined to tapering columns in outer regions and near the aerial cut surface. In more central regions a gradient in colour and texture can be seen as colonisers from basal regions replace species higher up. Replacing species include Psathyrella hydrophilum (Ph), and Ascocorynesarcoides (As), which in turn were followed by a mixture of A. sarcoides, a Verticillium sp. (V) and a perithecial ascomycete (pa). Scale bar represents 5 cm. (c) A longitudinal wood section from which mycelinm has grown directly out of the wood, indicating the presence of C. oersicolor (Cv) and X. hypoxylon (Xh), whilst outgrowth of cords indicates the concurrent presence of T. platyphylla (Tp). Scale bar represents 1 cm. b
63
64
Ascomycotina Lopadostoma turgidum. No data are presented for Lenzites betulina and Phanerochaete velutina as the wood was too decayed for accurate determination of density. Data on moisture contents of wood occupied by different species have not been presented for two reasons. Firstly, determinations were not all made at the same time and secondly it is difficult to interpret moisture content data when sample densities differ (cf. discussion by Boddy [13]). Particularly striking, however, was the observation that columns of X. hypoxylon were always very dry, irrespective of the moisture regimes in surrounding decay regions. When logs were sectioned and the pseudosclerotial plates between X. hypoxylon and adjacent decay columns were severed, water passed from the latter columns into wood occupied by X. hypoxylon (Fig. 2).
4.2. Spatial distribution and interactions of fungi in wood
Replacement of one fungus by another in wood was identified on the basis of several criteria. Firstly, direct association of a fruit body of one species with a decay column containing the replacing species. Secondly, occurrence, in a domain occupied by the replacing species, of relic zone lines characteristic of another species. In this case there was usually a marked change in physical properties (e.g., mechanical resistance) of the wood, resulting in a secondary pattern superimposed on the primary pattern of original decay columns (Fig. 3a). The third criterion was a gradual change in mechanical resistance, colour or texture of the wood, accompanied by a change in species isolated from the same decay region (Fig. 3b). In some cases, replacement was indicated by two species being intermixed (Fig. 3c). Replacement and deadlock interactions between decay fungi in the logs are shown in Table 2. It should be noted that replacement has been reported only where there was definite evidence of the identity of the two species involved. The spatial distribution of decay fungi in the logs was varied, but for the main species characteristic patterns could be identified. Of the quantitatively most significant species X. hypoxylon, C. versicolor and S. hirsutum apparently
colonised aerially. X. hypoxylon was typically found in wood near the external surface, when this was exposed to the air, and occupied large volumes of wood in columns which tapered towards the basal cut surface (Fig. 3b). C. oersicolor usually occurred in central regions in the top half of the logs but, in those which had apparently fallen over early on in the experiment, columns sometimes extended from one cut surface to the other. S. hirsutum had similar distributional patterns to C. versicolor but was usually present only as small columns. The cord-forming fungi H. fasciculare, Phal. impudicus and T. platyphylla formed large columns originating from the base of logs and often extended to over half way up, and had clearly replaced fungi in many different decay columns (Fig. 3a). A. bulbosa occupied large volumes of wood located in all regions of the logs but in some was precluded from regions near the soil where it was being replaced by cord-forming fungi. A particularly interesting interaction occurred between Ph. velutina and A. bulbosa in one log after sectioning. Prior to sectioning the interaction appeared to be deadlock. Subsequently, however, Ph. velutina grew out from its territory as cords and traversed several centimetres of wood, occupied by A. bulbosa, before dedifferentiating into individual hyphae and replacing the latter. The late colonizers P. hydrophilum, L. betulina and Lo. turgidum had very different distributions. P. hydrophilum was predominantly found in inner regions where it had apparently replaced C. oersicolor, S. hirsutum and X. hypoxylon. L. betulina was only found in two logs, but it occupied most of the volume of these. In these logs the wood had evidently been previously colonised mainly, but not exclusively, by C. versicolor. The ascomycete Lo. turgidum appeared to colonise from the soil and formed heterogeneous areas of decay which resulted from replacement of some of the aerial colonisers (Table 2). When sections were incubated in the laboratory, Lo. turgidum decayed the wood rapidly, producing a brown-rot. Ascocoryne sarcoides was the only other ascomycete commonly isolated and was often found replacing X. hypoxylon in wood close to the soil. It usually colonised from the latter and was
65 Table 2 Interactions between wood-rotting fungi in logs 51 months after exposure Abbreviations: Ab, Armillaria bulbosa; Cm, Coprinus micaceus; Cv, Coriolus versicolor; Hf, Hypholoma fasciculare; Lb, Lenzites betulina; Pi, Phallus impudicus; Pv, Phanerochaete velutina; Ph, Psathyrella hydrophilum; Sb, Sistotrema brinkmanii; Sh, Stereum hirsutum; Tp, Tricholomopsis platyphylla; As, Ascocoryne sarcoides; Lt, Lopadostoma turgidum; Xh, Xylaria hypoxylon.
Basidiomycotina
Ascomycotina
Fungus
Replaced
Deadlock
Replaced by
Armillaria bulbosa Coprinus spp. Coriolus oersicolor Hypholoma fasciculare Lenzites betulina Phallus impudicus Phanerochaete oelutina Psathyrella hydrophilum Sistotrema brinkmanii Stereum hirsutum Tricholomopsis platyphylla
Xh, Sh, Cv Cv, Xh
Pv
Pv, Pi, Tp
Sh, Xh
Ab, Cm, Hf, Lb, Pi, Pv, Ph, Tp, Sb, Lt
Ascocoryne sarcoides Lopadostoma turgidum Xylaria hypoxylon
Cv, Xh Cv, Xh Ab, Cv, Xh Ab, Cv, Sh, Xh Cv, Sh, Xh Cv, Xh
Ab
Cv, Xh
Ab, Pv, Tp, Ph
Ab, Cv, Sh, Xh Xh Cv, Xh
frequently accompanied by mucoraceous fungi and Deuteromycotina from the soil. These fungi were mostly restricted to small volumes of wood or confined to highly decayed regions. Trichoderma species were however, sometimes confined to clearly demarcated decay columns of low density (0.08-0.23 g. cm-3; Table 1), and had apparently replaced the previous occupant. However, it should be noted that it is always difficult to rule out the possibility that Trichoderma spp. are contaminants. Of the other Deuteromycotina decay species it was interesting to note that a Cordana sp. was found growing specifically in interaction zones between basidiomycete decay columns. 4.3. Fungal interactions in culture Results of interaction experiments on MA, under the two different gaseous regimes, are given in Table 3. The outcome of most of the interactions was clearcut being either a deadlock, in which neither fungus became dominant, or replacement of one fungus by another. Pairings in which A. bulbosa or X. hypoxylon were overgrown by opposing fungi were classed as replacement but were difficult to interpret as both seal themselves off within pseudosclerotial plates, and retained the potential for regrowth when suitable conditions
Ab, Cm, Hf, Lt, Lb, Pi, Pv, Ph, Tp, Sb, As, Lt Cv, Sh
were provided. Other difficulties in classification of outcome occurred in some of the pairings involving cord-forming fungi. For example, Ph. velutina and S. hirsutum both replaced the mycelial colony of Phal. impudicus, but the latter grew out as cords from the margin of the colony distant from the replacing fungi (Fig. 4). A hierarchy in combative ability can be seen in the results obtained under normal atmospheric
Fig. 4. Interaction between Phanerochaete velutina (fight) and Phallus impudicus (left) on 2% malt agar at 25 o C. Ph. velutina replaces the mycelium of PhaL impudicus although the latter is able to 'escape' by producing mycelial cords.
66 Table 3 Outcome of interactions between wood-rotting Ascomycotina and Basidiomycotina on 2% malt agar, under two different gaseous regimes Abbreviations: As for Table 2; ~ colonies did not meet; b overgrowth occurred but overgrown species could still be reisolated. Fungus
Gaseous regime
Basidio- Armillaria mycotina bulbosa
Atmospheric 30% CO2, 5% 02
Coriolus versicolor Hypholoma fasciculare
Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02
Lenzites betulina
Atmospheric 30% CO2, 5% 02
Phallus impudicus Phanerochaete velutina Psathyrella hydrophilum
Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric
Sistotrema brinkmanii Stereum hirsutum Tricholomopsis platyphylla Ascomycotina
30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02
Replaced
Sh Pi, Pv, Xh Ab, Cv, Lb, Pi, Pv, Sb, Sh, Lt, Xh. Pi, Pv, Ph, Xh.
Ab, Cv, Ph, Sh, Lt, Xh. Cv b, Hf, Pi, Sh, Lt, Xh. Ab, Cv, Pi, Pv, Xh. Ab, Cv, Pv, Ph, Sh, Lt. Ab, Pi, Pv, Tp, Xh.
Lopadostoma Atmospheric turgidum 30% CO2, 5% 02 Xylaria hypoxylon
Atmospheric 30% CO 2, 5% 02
Ab.
conditions. Thus, A. bulbosa, Lo. turgidum and X. hypoxylon were least c o m b a t i v e ; C. versicolor and S. hirsutum were b e t t e r c o m b a t a n t s ; Phal. impudicus, Ph. velutina a n d T. platyphylla were m o r e c o m b a t i v e still; and H. fasciculare, L. Betulina, P. hydrophilum and Sis. brinkmanii were most combative. O u t c o m e s were s o m e t i m e s m o d i f i e d u n d e r inc r e a s e d CO2 a n d r e d u c e d 0 2 regimes, the b a l a n c e u s u a l l y b e i n g shifted slightly f r o m d e a d l o c k to r e p l a c e m e n t or vice versa. However, with s o m e p a i r i n g s the o u t c o m e s were s u b s t a n t i a l l y a l t e r e d f r o m c o m p l e t e r e p l a c e m e n t b y o n e species to corn-
Replaced by Hf, Lb, Pv, Sb, Xh. Lb, Ph, Sb, Sh
Ab b, Cv, Lb, Sb, Sh, Tp b, Lt. Pi, Ph,Tp, Lt, Xh. Hf, Ph, Sb, Lt a.
Ab, Cv, Pv, Sb, Sh. Ab, Cv, Pi, Pv, Sh, Tp, Xh. Cv, Tp, Xh.
Ab, Pi, Pv, Xh. Pv, Ph, Sh. Sb.
Deadlock Cv, Pi, Sh, Tp, Lt a, Ph Cv, Hf b, Pi b, Pv, Tp, Lt a, Xh. Ab, Lt, Xh. Ab, Hf, Sb, Sh, Lt. Tp.
Hf, Lb, Pi, Pv, Ph b, Sb, Tp. Lb, Ph, Tp. Ph.
Hr.
Ab, Lb, Pv, Sb. Abb, Pv a, Zpb, Xh. Pi. Ab, Pi ~, Tp, Lt ~, Xh. Ab, Lb.
Hf, Ph. Cv, Hf, Lb, Ph, Sb, Sh. Hf, Lb, Sb, Tp. Cv, Hf, Lb, Ph, Sb, Sh. Pv, Sb, Tp.
Lb, Sb, Sh, Tp, Lt. Pi, Xh. Cv, Hf, Lb, Ph, Sh, Lt. Ab, Lt, Xh, Cv, Hf, Ph, Sb, Tp, Lt a. Ab, Cv, Hf, Lb, Lt, Xh. Ab, Cv, Hf b, Pi b, Pv, Ph, Sh, Lt, Xh.
Hf. Hf, Lb, Tp. Cv, Hf, Lb, Pv, Ph, Sb, Tp. Lb. Pi, Sb. Lb.
Ab a, Cv, Lb, Sh, Tp, Xh a. Hf, Pv, Ph, Sb. Ab a, Cv, Hf, Lb a, Pv a, Ph, Sb, Sh, Tp, Xh a. Cv, Lb, Sb, Sh, Tp, Lt a. Cv, Hf, Pi, Pv, Ph. Ab, Pi, Pv, Tp, Lt a Hf, Lb, Ph, Sb, Sh.
plete r e p l a c e m e n t b y the other. Thus, C. versicolor r e p l a c e d Phal. impudicus and Ph. velutina; H. fasciculare r e p l a c e d P. hydrophilum; P. hydrophilum and S. hirsutum r e p l a c e d Ph. velutina; and Sis. brinkmanii r e p l a c e d T. platyphylla u n d e r increased CO2, whereas the reverse was true u n d e r n o r m a l a t m o s p h e r e s . It is evident that the c o m b a t i v e a b i l i t y of the c o r d - f o r m i n g fungi d e c r e a s e d u n d e r raised C O 2 regimes; the n u m b e r of species t h a t they were a b l e to r e p l a c e d e c r e a s e d whilst the n u m b e r o f species able to replace t h e m increased. O u t c o m e of i n t e r a c t i o n s o b s e r v e d in logs were n o t always w h a t m i g h t have b e e n p r e d i c t e d f r o m
67 studies on agar, although they only varied from deadlock to replacement. For example, there was evidence of replacement of C. versicolor by A. bulbosa in logs, but only deadlock on agar.
5. DISCUSSION The results presented here extend earlier observations [7-9], and provide an indication of the change in species composition during the four and a half years since felling. Care must be taken, however, when comparing present data with those from earlier samplings as it had previously been found that different treatments sometimes resuited in differences in community structure. The original treatments were no longer apparent for all logs at the final sampling, but where known no differences could be detected in the presence of species in logs subjected to initially different treatments. However, there was, as found at the previous sampling, a tendency for series A logs to be more decayed than others. In previous investigations [7-9], Ch. purpureum and various Hypoxylon species, mainly Hyp. nummularium, were present at the first sampling; Ch. purpureum was infrequent after 52 weeks and Hyp. nummulariurn was declining after 97 weeks, and neither were found in this study. B. adusta, S. hirsutum, C. versicolor and X. hypoxylon had also colonised early, presumably as spores. B. adusta declined after 97 weeks but S. hirsutum persisted, albeit only in small volumes in a few logs, until the final sampling. C. versicolor and X. hypoxylon still occupied large volumes in 45 and 90%, respectively, of the logs sampled in the present study, although the preponderance of X. hypoxylon may reflect original treatments as indicated above. Cord- and rhizomorph- forming fungi had also arrived quickly [8]; A. bulbosa, Tricholomopsis platyphylla and Phallus impudicus were present but patchily distributed after 3 months, and Phanerochaete velutina was present after 6 months. The cord-forming fungi were aggressive combatants which gradually replaced aerial colonisers and by the final sampling had come to occupy large volumes, extending from the bases. A. bulbosa, which was present in over three quarters
of the logs sampled after 6 months and 1 year, was still present in half of the logs that we sampled after four and a half years, but again it is possible that the apparent prevalence of A. bulbosa reflected the original treatments. The communities in the logs examined in the earlier studies [7-9] were dominated first by organisms exhibiting ruderal strategies and then replaced by combative and stress-tolerant fungi [11]. The strategies adopted by the fungi present in the logs four and a half years after felling are considered below, including a number of additional fungi, which had not been detected at earlier samplings, viz. the Basidiomycotina Coprinus spp., Lenzites betulina, Psathyrella hydrophilum and Sistotrema brinkmanii, the Ascomycotina Lopadostoma turgidum and various mucorales and Deuteromycotina from the soil. C. versicolor was combative both in attack, replacing some of the fungi which colonised from the surface, and in defence of its domain, which could account for its occupation of large volumes of wood for a long period. By the final sampling however, C. versicolor was beginning to be replaced by a number of cord-forming fungi invading from lower regions and by later colonisers. These results were largely backed up by the results of the studies on agar under normal atmospheric conditions. However, it is interesting to note that under conditions of reduced aeration cord-forming fungi, Sis. brinkmanii and Lo. turgidum appear to be less combative and were unable to replace C. versicolor. This may at least partially explain the survival of C. versicolor in inner volumes of wood and the late appearance of fungi replacing this species, since the depressed 02 levels and elevated CO2 levels which are commonly reported in rotting wood (e.g., Ref. 12) tend to be alleviated as porosity increases concomitant with decomposition [13]. X. hypoxylon, in contrast to C. versicolor, rapidly occupied large volumes soon after exposure but did not encroach into other decay columns. In culture it was very poor at replacement and was overgrown by many opposing fungi. However, it was unclear whether it was itself replaced, since it produced pseudosclerotial plates within which it became sealed. In wood, decay
68 columns of X. hypoxylon were also surrounded by pseudosclerotial plates and were much drier than adjacent wood which suggests that X. hypoxylon considerably modifies the water regime of the wood that it occupies. It is also tempting to speculate that pseudosclerotial plates and low water content contribute to its defensive ability. Cord-forming fungi were the most common replacers of X. hypoxylon and would presumably be aided in this respect by their ability to translocate water. There was evidence that A. bulbosa had replaced C. versicolor, S. hirsutum and X. hypoxylon but that it was itself being replaced by cord-forming fungi. The latter interaction has been seen in a number of other studies, but it is interesting to note here that cord-forming fungi often occupied adjacent decay columns to A. bulbosa without apparently encroaching on its territory. Again, this may be related to differences in the relative combative abilities of these fungi under different abiotic regimes and also to the production by A. bulbosa of pseudosclerotial plates. A. bulbosa was often found in relatively undecayed wood or in water-saturated wood, resulting in environmental conditions which may be unfavourable for combat of cord-forming fungi. This was further emphasised by the fact that when wood was sectioned, and hence aerated, Ph. velutina often replaced A. bulbosa. In view of the foregoing, it is clear that the balance of species within a community may change without the arrival of other colonisers simply as a result of the effect of changing microclimatic conditions on the combative ability of one fungus relative to that of another, and this is further supported by studies of attached ash (Fraxinus excelsior) branches [14,15]. Further, combative ability may be affected by other factors. For example, when one cord-forming fungus is paired against another, in the form of colonised wood blocks placed on non-sterile soil, the outcome is delicately balanced, depending on which cords arrive at the wood blocks first and on the size of domain of wood occupied [16; Dowson, C.G., Rayner, A.D.M. and Boddy, L., unpublished data). Of the species that were not found until the final sampling, both P. hydrophilum and Sis.
brinkmanii were very combative on agar, although it was difficult to determine which fungi they had replaced in wood. Under normal atmospheric conditions neither of them were demonstrably more combative than cord-forming fungi, and were in fact replaced by some of the latter. P. hydrophilum and Sis. brinkmanii were, however, better combatants than the cord-forming fungi under conditions of reduced aeration. Thus, although replacement of fungi in wood may again depend to some extent on microclimatic factors, the ability of P. hydrophilum and Sis. brinkmanii to colonise late on in the development of the community may not be entirely related to combative ability per se but to other factors related to well-decayed wood. This was even more apparent with the Ascomycotina Lo. turgidum which was found in well-decayed areas of brown-rotted wood, but was unable to replace any other species in culture. This is probably an example of a stresstolerant fungus becoming dominant at late stages of community development. Likewise, soil Deuteromycotina and mucoraceous fungi colonise well-decayed wood where it is in contact with the soil, and are also common following invasion by invertebrates [17]. A particularly interesting colonization stategy was seen at the final sampling in two logs, which had formerly contained a number of columns of C. versicolor occupying extensive volumes and a few smaller columns containing other species including X. hypoxylon and A. bulbosa. These logs were occupied almost exclusively by single individuals of the air-borne colonizer Lenzites betulina, which is mycoparasitic specifically on members of the genus Coriolus, although it can replace some other species in culture as a front of mycelium which gradually encroaches into the territory of the opponent [16]. It has been suggested that L. betulina utilizes its ability to mycoparasitize C. versicolor not just directly as a means of obtaining nutrition but for capture of large volumes of wood which it can subsequently decompose [16]. It can then extend its already large spatial domain by replacing other species.
69 ACKNOWLEDGEMENTS T h a n k s are d u e to t h e M e x i c a n g o v e r n m e n t for f u n d i n g I . H . C . , to D a v i d C o a t e s for a l l o w i n g us to use logs r e m a i n i n g at t h e e n d o f his e x p e r i m e n t , to t h e F o r e s t r y C o m m i s s i o n for a l l o w i n g us to u s e t h e site, a n d to L a n c e M o r k o t a n d N o r m a n W i l l i a m s for s e c t i o n i n g the logs.
[9]
[10]
[11] REFERENCES [1] Rayner, A.D.M. and Todd, N.K. (1979) Population structure and dynamics of fungi in decaying wood. Adv. Bot. Res. 7, 333-420. [2] Rayner, A.D.M. and Boddy, L. (1986) Population structure and the infection biology of wood-decay fungi in living trees. Adv. Plant Pathol. 5, 119-160. [3] Ueyama, A. (1966) Studies on the succession of higher fungi on felled beech logs (Fagus crenata) in Japan. Mater. Org. 1, 325-332. [4] Kaarik, A. (1967) Colonization of pine and spruce poles by fungi after six months. Mater. Org. 2, 97-108. [5] Kaarik, A. (1968) Colonization of pine and spruce poles by soil fungi after twelve and eighteen months. Mater. Org. 3, 185-198. [6] Kaarik, A. (1974) Decomposition of wood. In: Biology of Plant Litter Decomposition (Dickinson, C.H. and Pugh, G.J.F., Eds.), pp. 129-174, Academic Press, London. [7] Coates, D. and Rayner, A.D.M. (1985) Fungal population and community development in cut beech logs. I. Establishment via the aerial cut surface. New Phytol. 101, 153-171. [8] Coates, D. and Rayner, A.D.M. (1985) Fungal population and community development in cut beech logs. II. Estab-
[12]
[13]
[14]
[15]
[16]
[17]
lishment via the buried cut surface. New Phytol. 101, 173-181. Coates, D. and Rayner, A.D.M. (1985) Fungal population and community development in cut beech logs. III. Spatial dynamics, interactions and strategies. New Phytol. 101,183-198. Boddy, L. and Thompson, W. (1983) Decomposition of suppressed oak trees in even-aged plantations. I. Stand characteristics and decay of aerial parts. New Phytol. 93, 261-276. Cooke, R.C. and Rayner, A.D.M. (1984) Ecology of Saprotrophic Fungi. Longman, London. Hintikka, V. and Korhonen, K. (1970) Effects of carbon dioxide on the growth of lignicolous and soil-inhabiting Hymenomycetes. Comm. Inst. For. Fenn. 69.5, pp. 28. Boddy, L. (1984) The microenvironment of basidiomycete mycelia in temperate deciduous woodlands. In: The Ecology and Physiology of the Fungal Mycelium (Jennings, D.H. and Rayner, A.D.M., Eds.), Cambridge University Press, Cambridge. Boddy, L., Gibbon, O. and Grundy, M. (1985) Ecology of Daldinia concentrica from ash: effect of abiotic variables on mycelial extension and interspecific interactions. Trans. Br. Mycol. Soc. 85, 201-211. Boddy, L., Bardsley, D. and Gibbon, O. (1987) Fungal communities in attached ash branches. New Phytol. (in press). Rayner, A.D.M., Boddy, L. and Dowson, C.G. (1987) Temporary parasitism of Coriolus spp. by Lenzites betulina: a strategy for domain capture in wood decay fungi. FEMS Microbiol. Ecol. 45, 53-58. Swift, M.J. and Boddy, L. (1984) Animal-microbial interactions during wood decompositions. In: Invertebrate-Microbial Interactions (Anderson, J.M., Rayner, A.D.M. and Walton, D.W.H., Eds.), pp. 89-131, Cambridge University Press, Cambridge.
59
FEC 00149
Structure and development of fungal communities in beech logs four and a half years after felling I.H. C h a p e l a a, L y n n e B o d d y
a
and A.D.M. Rayner b
a Department of Microbiology, University College, Newport Road, Cardiff, and b School of Biological Sciences, Universityof Bath, Claverton Down, Bath, U.K.
Received 10 June 1987 Revision received4 September1987 Accepted 5 September 1987 Key words: Succession; Interspecific interaction; Replacement mechanism; Wood decay; Mycelial cord
1. SUMMARY The spatial structure of fungal communities which have developed, following colonization aerially and from the soil, in beech logs four and a half years after felling is described, and mechanisms for change are examined. Comparison with community structure at earlier samplings revealed a temporal change which was largely, but not completely, reflected by a hierarchy of combative ability. The most abundant species, both in terms of volume and number of logs occupied, were Xylaria hypoxylon, Coriolus versicolor and Armillaria bulbosa, all of which had persisted for a long time: after only six months the former two had occupied large volumes of wood, whilst A. bulbosa had begun to colonise subcortically. Some of the earliest colonisers, including Bjerkandera adusta and Chondrostereum purpureum, were not detected at the final sampling. Cord-forming fungi colonising from the soil were prevalent in basal regions after one year, and after four and a half years
Correspondence to: L. Boddy, Department of Microbiology, University College, Newport Road, Cardiff CF2 1TA, U.K.
were well established and evidently replaced a number of early colonisers. Several species which had not been found at earlier samplings were well established by the final sampling, These were Lenzites betulina, Psathyrella hydrophilum, Sistotrema brinkmanii and the Ascomycotina Lopadostoma turgidum. In addition, soil Deuteromycotina and mucoraceous fungi were present in some columns of well-decayed wood.
2. I N T R O D U C T I O N As decomposition of wood proceeds, the mycofloral composition and spatial structure of the communities change [1,2], but until recently most studies have been essentially floristic (e.g., Refs. 3-6), omitting important spatial considerations. Further, it is rare for mycofloral studies to be carried out in conjunction with those on decay rate, preventing assessment of the effect of community structure on decay. Neither is it usual for either type of study to extend for longer than 2 to 3 years - the typical length of a research award. Recently, however, Coates and Rayner [7-9] have described the spatial and temporal patterns of
0168-6496/88/$03.50 © 1988 Federation of European MicrobiologicalSocieties
60 establishment from aerially exposed and buried cut surfaces of beech logs over a 97-week period. These observations are extended in this paper where we describe community structure and state of decay, four and a half years after felling, and examine mechanisms for change.
3. MATERIALS A N D M E T H O D S
3.1. Site description and experimental design The experimental site was a stand of oak
(Quercus robur L.) with occasional beech (Fagus syloatica L.) in the Sallow Valets Inclosure, Forest of Dean, Gloucestershire (N.G. Ref. SO 611145). The stand had not been thinned prior to initiation of the experiment, but most beech trees were felled about 1 year before the final sampling, and the boles and brash were left in piles on the site. Details of soil and vegetation characteristics for an adjacent site are given elsewhere [10]. The experimental design is described in detail elsewhere [7]. Briefly, freshly felled beech logs (30-40 cm length, 10-20 cm diameter) were placed uptight, with their bases buried to a depth of approximately 10 cm, in March 1980. Some of these were allowed to be colonised naturally (series A), in others a slice 2 cm thick was removed from the upper surface at each sampling (series B), while a third group was treated with spore suspensions of wood-rotting Basidiomycotina (series C and D). Logs from each series were sampled on seven occasions during the first 129 weeks [7-9], and 50 remaining logs described in this paper were collected in November 1984, four and a half years after initial exposure.
3.2. Analysis of fungal communities The presence and distribution on the wood surface of recognisable macroscopic fungal structures, e]g., mycelium, cords and sporophores, were recorded. The orientation of geotropic structures indicated whether the position of the log had changed during the experiment due to large mammal activity or forestry operations. Each log was then sectioned on a band saw to reveal the three-dimensional patterns of decay. The high variation in state of decay of different logs made
standardization of the sectioning procedure impractical, but whenever possible transverse sections from the middle and both ends were made. The remainder of each log was then sectioned longitudinally. Patterns of decay, including zone lines and stained regions, were examined to identify the range of species involved, the most important columns (in terms of volume), and to reveal the probable origin of each. This was further aided by direct incubation of some sections in polythene bags at room temperature ( 1 8 - 2 0 ° C ) for up to 3 months, which allowed outgrowth of identifiable mycelium and occasionally fruit bodies. Selected individual decay columns were dissected from the logs. Samples were taken from these and volume, fresh weight and oven dry weight were measured to obtain estimates of density and water content. Fungal isolations were made by aseptically transferring small chips of wood on to plates of 2% (w/v) malt agar (MA), MA containing 10 ppm Novobiocin plus 50 ppm Benomyl, and MA acidified with lactic acid to approximately pH 3.5. These were incubated for up to 4 months, after which the resulting cultures were identified. When single decay columns exhibited variation in colour, texture or mechanical resistance isolations were made from throughout the decay column to ensure that differences in species composition were detected.
3.3. lnterspecific interactions Single isolates of 12 of the wood-rotting species were paired in all combinations, by placing 4-mm diameter inocula 3 cm apart on 9-cm plates of MA. Isolates of different species were inoculated at different times so that they met at the centre of the plate. Plates were incubated at 25 ° C, for up to 4 weeks under normal atmospheric conditions, and for up to 10 weeks under an atmosphere of 30% CO z, 5% 02. The latter gaseous combination was obtained in 3-1jars containing up to six plates and was renewed twice a week. 4. RESULTS
4.1. Species occurrence and state of decay The position of many of the logs was disturbed,
61
Ascomycotina were isolated, of which Xylaria hypoxylon, Armillaria bulbosa and Coriolus versicolor
partly as a result of forestry operations, and many of the tags identifying the original treatment were lost. For those which were identifiable, no difference in species composition was obvious, neither was it possible to detect a statistically significant difference (P < 0.05) in mean state of decay (g. cm-3). Untreated logs (series A) were slightly more decayed (0.29 + 0.4 g - c m -3) than series B and C logs (0.37 + 0.07 g. cm-3 and 0.36 _ 0.03 g. cm -3) but low sample numbers (5, 5 and 4, respectively) would make detection of differences unlikely. However, wood occupied by different species showed considerable differences in the amount of decay (see below), and overall density appears to be affected more by composition of the decomposer community at later stages than by initial treatment effects. Results for all logs are therefore treated together. Table 1 presents the frequency with which wood-rotting fungi were detected in all logs, combining results from isolation, direct incubation and presence of macroscopic fungal structures. Fourteen species of Basidiomycotina and eight
occurred most frequently, being found respectively in 90, 50 and 46% of logs. They also occupied the largest volumes of wood, although this was not quantified. In addition, five other Ascomycotina were found fruiting on the surface but were not isolated from the wood. These were Dasyscyphus virgineus (4% of logs), Diatrype disciformis (2% of logs), Lasiosphaeria spermoides and L. ovina (18% of logs) and Melanommapulvis-pyrius (6% of logs). The maximum number of species of higher fungi found in any log was seven with a modal value of four (Fig. 1). This was independent of the number of columns sampled in each log. Mucoraceous fungi and Deuteromycotina were isolated from most logs, and included species of
Acremonium, Cordana, Fusarium, Mucor, Paecilomyces, Penicillium, Phialophora, Torula, Trichoderma, Verticillium and sterile hyaline and dematiaceous fungi. Trichoderma spp. were very common, being found in over 90% of the logs. The state of decay (as represented by density)
Table 1 Frequency of occurrence of predominant fungi and state of decay of wood (density; g . c m - 3 ) in 50 logs, 51 m o n t h s after exposure, irrespective of treatment Coprinus spp. includes Coprinus micaceus and Ozonium sp. Fungus
Basidiomycotina
Ascomycotina
Frequency
Density ( g . c m - 3)
Coefficient of
Mean %
variation
weight loss
0.12-0.50 0.12-0.30 0.09-0.13
31.11 31.67 25.45
46.3 73.1 83.6
0.28+0.10 0.30+0.21 0.36_+0.12
0.22-0.38 0.18-0.51 0.28-0.46
26.07 51.33 24.17
58.2 55.2 46.3
3
0.14_+0.21
0.01-0.23
82.14
79.1
19 9 4 3
0.47+0.03 0.36_+0.07 0.415:0.12 0.20-+0.09
0.34-0.55 0.13-0.45 0.31-0.52 0.16-0.26
10.85 27.50 21.95 25.50
29.9 46.3 38.8 70.1
13
0.16-+0.03 0.67
0.08-0.23 0.65-0.70
26.88
76.1
No. of logs
% of logs
n
Armillaria bulbosa Coriolus versicolor Psathyrella hydrophilum Phanerochaete velutina Stereum hirsutum Phallus impudicus Tricholomopsis platyphylla Sistotrema brinkmanii Hypholoma fasciculare Coprinus spp. Lenzites betulina
25 23 13
50 46 26 18 12 10 10 8 6 4 4
Xylaria hypoxylon (pure)
45
90 28 14 8 90
9 6 5 5 4 3 2
2
(replaCed)
Hypoxylon sp. Lopadostoma turgidum Ascocoryne sarcoides Trichoderma spp. Uncoionised wood
14
7 4 45
+ 95% confidence interval
range
20 14 2
0.36+0.05 0.18 5:0.03 0.11+0.09
4 4 4
62 15 00 O
"6 10
d Z
2
3 NO.
4 of
6 apeole8
per
7 log
Fig. 1. Frequency distribution of number of species of Ascomycotina and Basidiomycotina forming decay columns in individual logs.
o f c o l u m n s o c c u p i e d b y d i f f e r e n t f u n g i fall i n t o t h r e e b r o a d c a t e g o r i e s ( T a b l e 1). F i r s t l y , t h o s e w h i c h w e r e r e l a t i v e l y little d e c a y e d ( a v e r a g e g r e a t e r t h a n 0.4 g - c m - 3 ; a n d w i t h l o w v a r i a t i o n ) u s u a l l y c o n t a i n e d t h e A s c o m y c o t i n a Xylaria hypoxylon o r Hypoxylon serpens. W h e n X. hypoxylon w a s replaced density decreased. The second category, with an average density of 0.3-0.4 g. cm-3, comprises the cord- and rhizomorph-forming fungi
Armillaria bulbosa,
Phallus impudicus and Tri-
Fig. 2. Longitudinal section through wood containing columns of Coriolus oersicolor (Cv) and Xylaria hypoxylon (Xh). The columns of X. hypoxylon are surrounded by pseudosclerotial plates (psp) which when cut allow water into formerly dry regions (w) occupied by X. hypoxylon. Scale bar represents 1 cm.
cholomopsis platyphylla. T h e t h i r d c a t e g o r y , w i t h a n a v e r a g e d e n s i t y o f less t h a n 0.3 g - c m -3, c o m p r i s e s Coriolus versicolor, Hypholoma fasciculare, Psathyrella hydrophilum, Stereum hirsutum a n d the
Fig. 3. ('a) Transverse section from near the base of a log after direct incubation in an humid atmosphere. Xylaria hypoxylon (Xh) is present in peripheral regions although, as indicated by the presence of relic zone lines (rzl), formerly it occupied almost the entire section. Tricholomopsisplatyphylla (Tp) now occupies the majority of the central regions of the section and its mycelium has grown out of the wood in certain places. (b) Longitudinal section showing X. hypoxylon confined to tapering columns in outer regions and near the aerial cut surface. In more central regions a gradient in colour and texture can be seen as colonisers from basal regions replace species higher up. Replacing species include Psathyrella hydrophilum (Ph), and Ascocorynesarcoides (As), which in turn were followed by a mixture of A. sarcoides, a Verticillium sp. (V) and a perithecial ascomycete (pa). Scale bar represents 5 cm. (c) A longitudinal wood section from which mycelinm has grown directly out of the wood, indicating the presence of C. oersicolor (Cv) and X. hypoxylon (Xh), whilst outgrowth of cords indicates the concurrent presence of T. platyphylla (Tp). Scale bar represents 1 cm. b
63
64
Ascomycotina Lopadostoma turgidum. No data are presented for Lenzites betulina and Phanerochaete velutina as the wood was too decayed for accurate determination of density. Data on moisture contents of wood occupied by different species have not been presented for two reasons. Firstly, determinations were not all made at the same time and secondly it is difficult to interpret moisture content data when sample densities differ (cf. discussion by Boddy [13]). Particularly striking, however, was the observation that columns of X. hypoxylon were always very dry, irrespective of the moisture regimes in surrounding decay regions. When logs were sectioned and the pseudosclerotial plates between X. hypoxylon and adjacent decay columns were severed, water passed from the latter columns into wood occupied by X. hypoxylon (Fig. 2).
4.2. Spatial distribution and interactions of fungi in wood
Replacement of one fungus by another in wood was identified on the basis of several criteria. Firstly, direct association of a fruit body of one species with a decay column containing the replacing species. Secondly, occurrence, in a domain occupied by the replacing species, of relic zone lines characteristic of another species. In this case there was usually a marked change in physical properties (e.g., mechanical resistance) of the wood, resulting in a secondary pattern superimposed on the primary pattern of original decay columns (Fig. 3a). The third criterion was a gradual change in mechanical resistance, colour or texture of the wood, accompanied by a change in species isolated from the same decay region (Fig. 3b). In some cases, replacement was indicated by two species being intermixed (Fig. 3c). Replacement and deadlock interactions between decay fungi in the logs are shown in Table 2. It should be noted that replacement has been reported only where there was definite evidence of the identity of the two species involved. The spatial distribution of decay fungi in the logs was varied, but for the main species characteristic patterns could be identified. Of the quantitatively most significant species X. hypoxylon, C. versicolor and S. hirsutum apparently
colonised aerially. X. hypoxylon was typically found in wood near the external surface, when this was exposed to the air, and occupied large volumes of wood in columns which tapered towards the basal cut surface (Fig. 3b). C. oersicolor usually occurred in central regions in the top half of the logs but, in those which had apparently fallen over early on in the experiment, columns sometimes extended from one cut surface to the other. S. hirsutum had similar distributional patterns to C. versicolor but was usually present only as small columns. The cord-forming fungi H. fasciculare, Phal. impudicus and T. platyphylla formed large columns originating from the base of logs and often extended to over half way up, and had clearly replaced fungi in many different decay columns (Fig. 3a). A. bulbosa occupied large volumes of wood located in all regions of the logs but in some was precluded from regions near the soil where it was being replaced by cord-forming fungi. A particularly interesting interaction occurred between Ph. velutina and A. bulbosa in one log after sectioning. Prior to sectioning the interaction appeared to be deadlock. Subsequently, however, Ph. velutina grew out from its territory as cords and traversed several centimetres of wood, occupied by A. bulbosa, before dedifferentiating into individual hyphae and replacing the latter. The late colonizers P. hydrophilum, L. betulina and Lo. turgidum had very different distributions. P. hydrophilum was predominantly found in inner regions where it had apparently replaced C. oersicolor, S. hirsutum and X. hypoxylon. L. betulina was only found in two logs, but it occupied most of the volume of these. In these logs the wood had evidently been previously colonised mainly, but not exclusively, by C. versicolor. The ascomycete Lo. turgidum appeared to colonise from the soil and formed heterogeneous areas of decay which resulted from replacement of some of the aerial colonisers (Table 2). When sections were incubated in the laboratory, Lo. turgidum decayed the wood rapidly, producing a brown-rot. Ascocoryne sarcoides was the only other ascomycete commonly isolated and was often found replacing X. hypoxylon in wood close to the soil. It usually colonised from the latter and was
65 Table 2 Interactions between wood-rotting fungi in logs 51 months after exposure Abbreviations: Ab, Armillaria bulbosa; Cm, Coprinus micaceus; Cv, Coriolus versicolor; Hf, Hypholoma fasciculare; Lb, Lenzites betulina; Pi, Phallus impudicus; Pv, Phanerochaete velutina; Ph, Psathyrella hydrophilum; Sb, Sistotrema brinkmanii; Sh, Stereum hirsutum; Tp, Tricholomopsis platyphylla; As, Ascocoryne sarcoides; Lt, Lopadostoma turgidum; Xh, Xylaria hypoxylon.
Basidiomycotina
Ascomycotina
Fungus
Replaced
Deadlock
Replaced by
Armillaria bulbosa Coprinus spp. Coriolus oersicolor Hypholoma fasciculare Lenzites betulina Phallus impudicus Phanerochaete oelutina Psathyrella hydrophilum Sistotrema brinkmanii Stereum hirsutum Tricholomopsis platyphylla
Xh, Sh, Cv Cv, Xh
Pv
Pv, Pi, Tp
Sh, Xh
Ab, Cm, Hf, Lb, Pi, Pv, Ph, Tp, Sb, Lt
Ascocoryne sarcoides Lopadostoma turgidum Xylaria hypoxylon
Cv, Xh Cv, Xh Ab, Cv, Xh Ab, Cv, Sh, Xh Cv, Sh, Xh Cv, Xh
Ab
Cv, Xh
Ab, Pv, Tp, Ph
Ab, Cv, Sh, Xh Xh Cv, Xh
frequently accompanied by mucoraceous fungi and Deuteromycotina from the soil. These fungi were mostly restricted to small volumes of wood or confined to highly decayed regions. Trichoderma species were however, sometimes confined to clearly demarcated decay columns of low density (0.08-0.23 g. cm-3; Table 1), and had apparently replaced the previous occupant. However, it should be noted that it is always difficult to rule out the possibility that Trichoderma spp. are contaminants. Of the other Deuteromycotina decay species it was interesting to note that a Cordana sp. was found growing specifically in interaction zones between basidiomycete decay columns. 4.3. Fungal interactions in culture Results of interaction experiments on MA, under the two different gaseous regimes, are given in Table 3. The outcome of most of the interactions was clearcut being either a deadlock, in which neither fungus became dominant, or replacement of one fungus by another. Pairings in which A. bulbosa or X. hypoxylon were overgrown by opposing fungi were classed as replacement but were difficult to interpret as both seal themselves off within pseudosclerotial plates, and retained the potential for regrowth when suitable conditions
Ab, Cm, Hf, Lt, Lb, Pi, Pv, Ph, Tp, Sb, As, Lt Cv, Sh
were provided. Other difficulties in classification of outcome occurred in some of the pairings involving cord-forming fungi. For example, Ph. velutina and S. hirsutum both replaced the mycelial colony of Phal. impudicus, but the latter grew out as cords from the margin of the colony distant from the replacing fungi (Fig. 4). A hierarchy in combative ability can be seen in the results obtained under normal atmospheric
Fig. 4. Interaction between Phanerochaete velutina (fight) and Phallus impudicus (left) on 2% malt agar at 25 o C. Ph. velutina replaces the mycelium of PhaL impudicus although the latter is able to 'escape' by producing mycelial cords.
66 Table 3 Outcome of interactions between wood-rotting Ascomycotina and Basidiomycotina on 2% malt agar, under two different gaseous regimes Abbreviations: As for Table 2; ~ colonies did not meet; b overgrowth occurred but overgrown species could still be reisolated. Fungus
Gaseous regime
Basidio- Armillaria mycotina bulbosa
Atmospheric 30% CO2, 5% 02
Coriolus versicolor Hypholoma fasciculare
Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02
Lenzites betulina
Atmospheric 30% CO2, 5% 02
Phallus impudicus Phanerochaete velutina Psathyrella hydrophilum
Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric
Sistotrema brinkmanii Stereum hirsutum Tricholomopsis platyphylla Ascomycotina
30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02 Atmospheric 30% CO2, 5% 02
Replaced
Sh Pi, Pv, Xh Ab, Cv, Lb, Pi, Pv, Sb, Sh, Lt, Xh. Pi, Pv, Ph, Xh.
Ab, Cv, Ph, Sh, Lt, Xh. Cv b, Hf, Pi, Sh, Lt, Xh. Ab, Cv, Pi, Pv, Xh. Ab, Cv, Pv, Ph, Sh, Lt. Ab, Pi, Pv, Tp, Xh.
Lopadostoma Atmospheric turgidum 30% CO2, 5% 02 Xylaria hypoxylon
Atmospheric 30% CO 2, 5% 02
Ab.
conditions. Thus, A. bulbosa, Lo. turgidum and X. hypoxylon were least c o m b a t i v e ; C. versicolor and S. hirsutum were b e t t e r c o m b a t a n t s ; Phal. impudicus, Ph. velutina a n d T. platyphylla were m o r e c o m b a t i v e still; and H. fasciculare, L. Betulina, P. hydrophilum and Sis. brinkmanii were most combative. O u t c o m e s were s o m e t i m e s m o d i f i e d u n d e r inc r e a s e d CO2 a n d r e d u c e d 0 2 regimes, the b a l a n c e u s u a l l y b e i n g shifted slightly f r o m d e a d l o c k to r e p l a c e m e n t or vice versa. However, with s o m e p a i r i n g s the o u t c o m e s were s u b s t a n t i a l l y a l t e r e d f r o m c o m p l e t e r e p l a c e m e n t b y o n e species to corn-
Replaced by Hf, Lb, Pv, Sb, Xh. Lb, Ph, Sb, Sh
Ab b, Cv, Lb, Sb, Sh, Tp b, Lt. Pi, Ph,Tp, Lt, Xh. Hf, Ph, Sb, Lt a.
Ab, Cv, Pv, Sb, Sh. Ab, Cv, Pi, Pv, Sh, Tp, Xh. Cv, Tp, Xh.
Ab, Pi, Pv, Xh. Pv, Ph, Sh. Sb.
Deadlock Cv, Pi, Sh, Tp, Lt a, Ph Cv, Hf b, Pi b, Pv, Tp, Lt a, Xh. Ab, Lt, Xh. Ab, Hf, Sb, Sh, Lt. Tp.
Hf, Lb, Pi, Pv, Ph b, Sb, Tp. Lb, Ph, Tp. Ph.
Hr.
Ab, Lb, Pv, Sb. Abb, Pv a, Zpb, Xh. Pi. Ab, Pi ~, Tp, Lt ~, Xh. Ab, Lb.
Hf, Ph. Cv, Hf, Lb, Ph, Sb, Sh. Hf, Lb, Sb, Tp. Cv, Hf, Lb, Ph, Sb, Sh. Pv, Sb, Tp.
Lb, Sb, Sh, Tp, Lt. Pi, Xh. Cv, Hf, Lb, Ph, Sh, Lt. Ab, Lt, Xh, Cv, Hf, Ph, Sb, Tp, Lt a. Ab, Cv, Hf, Lb, Lt, Xh. Ab, Cv, Hf b, Pi b, Pv, Ph, Sh, Lt, Xh.
Hf. Hf, Lb, Tp. Cv, Hf, Lb, Pv, Ph, Sb, Tp. Lb. Pi, Sb. Lb.
Ab a, Cv, Lb, Sh, Tp, Xh a. Hf, Pv, Ph, Sb. Ab a, Cv, Hf, Lb a, Pv a, Ph, Sb, Sh, Tp, Xh a. Cv, Lb, Sb, Sh, Tp, Lt a. Cv, Hf, Pi, Pv, Ph. Ab, Pi, Pv, Tp, Lt a Hf, Lb, Ph, Sb, Sh.
plete r e p l a c e m e n t b y the other. Thus, C. versicolor r e p l a c e d Phal. impudicus and Ph. velutina; H. fasciculare r e p l a c e d P. hydrophilum; P. hydrophilum and S. hirsutum r e p l a c e d Ph. velutina; and Sis. brinkmanii r e p l a c e d T. platyphylla u n d e r increased CO2, whereas the reverse was true u n d e r n o r m a l a t m o s p h e r e s . It is evident that the c o m b a t i v e a b i l i t y of the c o r d - f o r m i n g fungi d e c r e a s e d u n d e r raised C O 2 regimes; the n u m b e r of species t h a t they were a b l e to r e p l a c e d e c r e a s e d whilst the n u m b e r o f species able to replace t h e m increased. O u t c o m e of i n t e r a c t i o n s o b s e r v e d in logs were n o t always w h a t m i g h t have b e e n p r e d i c t e d f r o m
67 studies on agar, although they only varied from deadlock to replacement. For example, there was evidence of replacement of C. versicolor by A. bulbosa in logs, but only deadlock on agar.
5. DISCUSSION The results presented here extend earlier observations [7-9], and provide an indication of the change in species composition during the four and a half years since felling. Care must be taken, however, when comparing present data with those from earlier samplings as it had previously been found that different treatments sometimes resuited in differences in community structure. The original treatments were no longer apparent for all logs at the final sampling, but where known no differences could be detected in the presence of species in logs subjected to initially different treatments. However, there was, as found at the previous sampling, a tendency for series A logs to be more decayed than others. In previous investigations [7-9], Ch. purpureum and various Hypoxylon species, mainly Hyp. nummularium, were present at the first sampling; Ch. purpureum was infrequent after 52 weeks and Hyp. nummulariurn was declining after 97 weeks, and neither were found in this study. B. adusta, S. hirsutum, C. versicolor and X. hypoxylon had also colonised early, presumably as spores. B. adusta declined after 97 weeks but S. hirsutum persisted, albeit only in small volumes in a few logs, until the final sampling. C. versicolor and X. hypoxylon still occupied large volumes in 45 and 90%, respectively, of the logs sampled in the present study, although the preponderance of X. hypoxylon may reflect original treatments as indicated above. Cord- and rhizomorph- forming fungi had also arrived quickly [8]; A. bulbosa, Tricholomopsis platyphylla and Phallus impudicus were present but patchily distributed after 3 months, and Phanerochaete velutina was present after 6 months. The cord-forming fungi were aggressive combatants which gradually replaced aerial colonisers and by the final sampling had come to occupy large volumes, extending from the bases. A. bulbosa, which was present in over three quarters
of the logs sampled after 6 months and 1 year, was still present in half of the logs that we sampled after four and a half years, but again it is possible that the apparent prevalence of A. bulbosa reflected the original treatments. The communities in the logs examined in the earlier studies [7-9] were dominated first by organisms exhibiting ruderal strategies and then replaced by combative and stress-tolerant fungi [11]. The strategies adopted by the fungi present in the logs four and a half years after felling are considered below, including a number of additional fungi, which had not been detected at earlier samplings, viz. the Basidiomycotina Coprinus spp., Lenzites betulina, Psathyrella hydrophilum and Sistotrema brinkmanii, the Ascomycotina Lopadostoma turgidum and various mucorales and Deuteromycotina from the soil. C. versicolor was combative both in attack, replacing some of the fungi which colonised from the surface, and in defence of its domain, which could account for its occupation of large volumes of wood for a long period. By the final sampling however, C. versicolor was beginning to be replaced by a number of cord-forming fungi invading from lower regions and by later colonisers. These results were largely backed up by the results of the studies on agar under normal atmospheric conditions. However, it is interesting to note that under conditions of reduced aeration cord-forming fungi, Sis. brinkmanii and Lo. turgidum appear to be less combative and were unable to replace C. versicolor. This may at least partially explain the survival of C. versicolor in inner volumes of wood and the late appearance of fungi replacing this species, since the depressed 02 levels and elevated CO2 levels which are commonly reported in rotting wood (e.g., Ref. 12) tend to be alleviated as porosity increases concomitant with decomposition [13]. X. hypoxylon, in contrast to C. versicolor, rapidly occupied large volumes soon after exposure but did not encroach into other decay columns. In culture it was very poor at replacement and was overgrown by many opposing fungi. However, it was unclear whether it was itself replaced, since it produced pseudosclerotial plates within which it became sealed. In wood, decay
68 columns of X. hypoxylon were also surrounded by pseudosclerotial plates and were much drier than adjacent wood which suggests that X. hypoxylon considerably modifies the water regime of the wood that it occupies. It is also tempting to speculate that pseudosclerotial plates and low water content contribute to its defensive ability. Cord-forming fungi were the most common replacers of X. hypoxylon and would presumably be aided in this respect by their ability to translocate water. There was evidence that A. bulbosa had replaced C. versicolor, S. hirsutum and X. hypoxylon but that it was itself being replaced by cord-forming fungi. The latter interaction has been seen in a number of other studies, but it is interesting to note here that cord-forming fungi often occupied adjacent decay columns to A. bulbosa without apparently encroaching on its territory. Again, this may be related to differences in the relative combative abilities of these fungi under different abiotic regimes and also to the production by A. bulbosa of pseudosclerotial plates. A. bulbosa was often found in relatively undecayed wood or in water-saturated wood, resulting in environmental conditions which may be unfavourable for combat of cord-forming fungi. This was further emphasised by the fact that when wood was sectioned, and hence aerated, Ph. velutina often replaced A. bulbosa. In view of the foregoing, it is clear that the balance of species within a community may change without the arrival of other colonisers simply as a result of the effect of changing microclimatic conditions on the combative ability of one fungus relative to that of another, and this is further supported by studies of attached ash (Fraxinus excelsior) branches [14,15]. Further, combative ability may be affected by other factors. For example, when one cord-forming fungus is paired against another, in the form of colonised wood blocks placed on non-sterile soil, the outcome is delicately balanced, depending on which cords arrive at the wood blocks first and on the size of domain of wood occupied [16; Dowson, C.G., Rayner, A.D.M. and Boddy, L., unpublished data). Of the species that were not found until the final sampling, both P. hydrophilum and Sis.
brinkmanii were very combative on agar, although it was difficult to determine which fungi they had replaced in wood. Under normal atmospheric conditions neither of them were demonstrably more combative than cord-forming fungi, and were in fact replaced by some of the latter. P. hydrophilum and Sis. brinkmanii were, however, better combatants than the cord-forming fungi under conditions of reduced aeration. Thus, although replacement of fungi in wood may again depend to some extent on microclimatic factors, the ability of P. hydrophilum and Sis. brinkmanii to colonise late on in the development of the community may not be entirely related to combative ability per se but to other factors related to well-decayed wood. This was even more apparent with the Ascomycotina Lo. turgidum which was found in well-decayed areas of brown-rotted wood, but was unable to replace any other species in culture. This is probably an example of a stresstolerant fungus becoming dominant at late stages of community development. Likewise, soil Deuteromycotina and mucoraceous fungi colonise well-decayed wood where it is in contact with the soil, and are also common following invasion by invertebrates [17]. A particularly interesting colonization stategy was seen at the final sampling in two logs, which had formerly contained a number of columns of C. versicolor occupying extensive volumes and a few smaller columns containing other species including X. hypoxylon and A. bulbosa. These logs were occupied almost exclusively by single individuals of the air-borne colonizer Lenzites betulina, which is mycoparasitic specifically on members of the genus Coriolus, although it can replace some other species in culture as a front of mycelium which gradually encroaches into the territory of the opponent [16]. It has been suggested that L. betulina utilizes its ability to mycoparasitize C. versicolor not just directly as a means of obtaining nutrition but for capture of large volumes of wood which it can subsequently decompose [16]. It can then extend its already large spatial domain by replacing other species.
69 ACKNOWLEDGEMENTS T h a n k s are d u e to t h e M e x i c a n g o v e r n m e n t for f u n d i n g I . H . C . , to D a v i d C o a t e s for a l l o w i n g us to use logs r e m a i n i n g at t h e e n d o f his e x p e r i m e n t , to t h e F o r e s t r y C o m m i s s i o n for a l l o w i n g us to u s e t h e site, a n d to L a n c e M o r k o t a n d N o r m a n W i l l i a m s for s e c t i o n i n g the logs.
[9]
[10]
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