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Growth of two terrestrial microfungi on submerged alder leaves
418
N otes and brief articles REFERENC ES
CHAMIER, A.-C. (198o). Pect inases in leaf degradation by aqu atic hyphomycetes. Ph .D . Thesis, Un iversity of London, U.K. CHAMIER, A.-C . & DIXON, P. A. ( 1982 a). Pectinases in leaf degradation by aquatic hyph omycetes, I. The field study . The colonization-pattern of aquatic hyphomyceres on leaf packs in a Su rre y st ream . Oecologia 5z, 109-115. CHAMIER, A.-C. & DI XON, P . A. ( 1982 b). Pectinases in leaf degradation by aquatic hyph omycetes : the enzymes and leaf maceration. J ournal of General M icrobiology uS, 2469"-2483. DARVILL, A., McNEIL, M. , ALBI!RSHEIM, P. & DELMER, D . P. (1980). The primary cell walls of flowering plants. In The Plant Cell (ed. N . E. Tolbert), pp. 92-157. New York , U .S .A. : Academic Press .
DI XON, M . & WEBB, E. C. (1979). Enzym es, 3rd ed. Lond on : Longmans. EGGLISHAW, H . J. (1968). The quantitative relat ionsh ip between bottom fauna and plant detritus in streams of different calcium concentrations . J ournal of A pplied Ecology 5, 731-740. HANKIN, L., POINCELOT, R. P . & ANAGNOSTAKIS, S. L. (1976). Micro-organisms from comp osting leaves; abilit y to produce extracellular degradat ive enzymes. M icrobial Ecology z, 296-308. KAUSHIK, N. K . & HYNES, H . B. N . (1971). The fate of dead leaves that fall into streams. Archiv fur Hydrobiologie 68, 597-607 . REXOVA-BENKOVA, L. & MARKOVIC, O. (1976). Pectic enzymes. Advances in Carbohydrate Chemistry and Biochemistry 33, 323-385.
GROWTH OF TWO TERRESTRIAL MICROFUNGI ON SUBMERGED ALDER LEAVES BY B. E. S. GODFREY
Departm ent of Biological Sciences, City of London Polytechnic, Old Castle Stre et, London, EI 7N T Epicoccum nigrum and Cladosporium cladosporioides decomposed alder leaves and were cellulolytic in submerged cultures. It is now well established that allochthonous plant & Klug, 1976). Suberkropp & Klug (1976) debris forms an important energy source for certain emphasize the need to investigate the ir ability to freshwater ecosystems (Petersen & Cummins, decompose submerged plant material so that their 1974; Hanlon, 1981). Attention has mostly been contribution to the overall process of plant litter paid to leaf litter and it has been shown that man y decomposition in aquatic habitats can be assessed. different microfungi may be isolated from submerDuring a sur vey of microfungi on plant leaf litter ged leaves including aquatic hyphomycetes, as well in a small flooded gravel pit in southern England, as species normally associated with terrestrial Hesketh (pers. cornm.) frequently isolated Cladohabitats (Kaushik & Hynes, 1968, 1971; Barlocher sporium cladosporioides (Fres.) de Vries and Epicoc& Kendrick, 1974; Suberkropp & Klug, 1976; cum nigrum L ink. The work described here was Chamier & D ixon, 1982). It appears that certain undertaken to assess their ability to degrade leaves microfungi, particularly the aquatic hyphomycetes, of alder (A lnus glutinosa ), which often const itute a ' condition ' imported plant debris making it more major component of submerged plant debris in palatable and nutritious for detritevores (Barlocher streams and ponds. Freshly fallen alder leaves were collected in & Kendrick, 1973, 1975; Marcus & Willoughby, November 1978, air-dried and stored at 4 DC until 1978). Aquatic hyphomycetes appear to be the dominant needed. Before use the leaves were washed in colonizers of leaf debris (Kaushik & Hynes, 1971; running tap water for 48 h, dried to constant weight Barlocher & Kendrick, 1974) and are generally at 800 and then placed singly in 250 ern" conical considered to be the main agent s of decomposition. flasks charged with 100 ern" of a mineral salts Recent studies by Suberkropp & Klug (198o) and medium containing MgSO, . 5H 20 , 0'075 g ; Chamier (1981) have confirmed that some, at least, KH 2PO" 0'075 g; KCI 0'03 g ; Ca(N03)2.4H20 ; have enzymes capable of breaking down pect ins, distilled water 1 I. After sterilizing by autoclav ing cellulose and hemicellulose. Although the aquatic at 1210 for 15 min flasks were inoculated with hyphomycetes seem to dominate the mycoflora, eithe r a small tuft of mycelium taken from the edge some authors consider that the so-called terrestrial of a z-week-old culture of E. nigrum or 0' 5-1 '0 em" fungi , pre sent on the plant det ritus when it falls into of a spore suspension prepared from an 8- to water , may play some part in the decomposition ro-day-old culture of C. cladosporioides, both grown process (Barlocher & Kendrick, 1974; Suberkropp on potato dextrose agar (PDA). Cultures were Trans. B r. my col. S oc. 81 (2), (1983)
Prim ed in Great Britain
Notes and brief articles Table
1.
Mean percentage dry weight loss of alder leaves C. cladosporioides 26'2
Control Expt.l Exptv a
18'3 16'7
Expt·3
2S'3
Incubation time (weeks) 21 21 22
E.nigrum 43.6 37'6
30·8
In each experiment the means are significantly different at the 95 % level or better.
incubated in the dark at 16-18°. Five replicate flasks were inoculated for each fungus and uninoculated flasks provided controls. Three similar experiments were set up and after incubation for 21 or 22 weeks leaves were harvested and dried to constant weight at 80°. At the end of the experiments mycelial growth could be seen on the leaves in inoculated flasks. Both fungi caused a significant loss in weight compared with the untreated controls (Table 1). E. nigrum caused greater loss in weight than C. cladosporioides and it was also observed that leaves inoculated with E. nigrum were soft and limp compared with the uninoculated controls. In two subsequent experiments designed to monitor progressive weight loss over 4 months, leaves which had been soaked in running water for 48 h and then dried to constant weight at 80° were sterilized individually by exposure to gamma rays from a cobalt source for 78 h. The irradiated leaves
45 40
~ ~
oS
35 30
:EOIl 25
'" 20 ~
,I!',. . -to---f----f
15 10 5
4
12
8
16
Weeks Fig. 1. Loss in weight of Alnus glutinosa leaves inoculated with E. nigrum (e) compared with uninoculated controls (x). Each point is the mean of five replicates; confidence limits set at P = 0'05 . Trans. Br . mycol. Soc. 81 (2), (1983)
35
*.
------£
.-_ •• -
.._.I1
10 5
4
12
8
16
Weeks Fig. 2. Loss in weight of Alnus glutinosa leaves inoculated with C. cladosporioides
were introduced singly into sterilized 250 ern" conical flasks containing mineral salts solution, and inoculated as described above . Sterility was confirmed by plating out fragments of treated leaves on to PDA . Leaves were harvested at 4-week intervals and dried to constant weight 80°. Leaves lost weight rapidly during the first rhonth and continued to do so in the case of E. nigrum (Fig. 1) so that by the end of week 16 the inoculated leaves had lost significantly more weight than the controls. In the case of C. cladosporioides (Fig . 2) there was little further loss in weight beyond week 8, although by the end of the experiment the inoculated leaves weighed significantly less than the controls. These results confirm the observations in the previous experiments that both fungi can decompose submerged alder leaves but that E. nigrum is more active than C. cladosporioides. Further experiments were conducted to test the cellulolytic ability of C. cladosporioides and E. nigrum. Five replicate flasks were prepared for each fungus containing 100 em" of the mineral salts medium plus one oven-dried, pre-weighed
Printed in Great Britain
Notes and brief articles
420
Table 2. Mean percentage dry weight loss of filter paper disks
Expt.1 Expt.2 Expt·3
Control 3'4 1 0"38 2'59
C" cladosporioides
E. nigrum
Incubation time (weeks)
13"52
5 10 10
11"19 12"02
In each experiment the means are significantly different at the 95 % level or better.
Whatman No.1 filter disk (5"5 em diam). After sterilization at 1210 for 15 min the cooled flasks were inoculated with either C. cladosporioides or E. nigrum as described above. Cultures were incubated in the dark at 16-18 0 • The disks were harvested and dried to constant weight. Both species were found to utilize pure cellulose and to a similar extent. The observations indicate that these two terrestrial species have the potential to participate in the breakdown of leaf litter in water and are in general agreement with the results obtained by Barlocher & Kendrick (1974) on maple-leaf disks inoculated with an unspecified Cladosporium sp. Most of the soluble organic substances are rapidly leached from dead leaves (Kaushik & Hynes, 1971), leaving a framework consisting largely of cellulose, hemicellulose and lignin, and the main agents of decomposition will be those organisms able to produce the enzymes capable of degrading these materials. Both fungi tested here were shown to be capable of degrading pure cellulose (filter paper). Flannigan (1970), working on one strain of C. cladosporioides and five of E. nigrum, found that all produced xylanases while three strains of E. nigrum produced cellulase capable of reducing the viscosity of carboxymethylcellulose. Recently Park (1982) demonstrated that both C. cladosporioides and E. nigrum metabolized filter-paper cellulose and that E. nigrum was more active than C. cladosporioides. These observations support the results obtained in this study, where E. nigrum caused a greater weight loss in alder leaves than C. cladosporioides. The softened texture of the alder leaves after incubation with E. nigrum is further evidence of its ability to break down the structural tissues. The extensive weight loss in the controls as well as the inoculated leaves in the first week of the time-course experiments, even after soaking for 48 h, is probably due to leaching of water-soluble substances from the leaves. However, the overall loss in weight provides further evidence of the plant decomposing potential of both fungi. Thus it is evident that at least two members of the 'terrestrial' mycoflora commonly present on plant litter at the time of leaf fall can be active in Trans. Br. mycol. Soc. 81 (2), (1983)
decomposition under water. The question remains, however, whether they do, in practice, participate in the decomposition process under natural conditions. Barlocher & Kendrick (1974) showed that in streams at temperatures of 1-100 aquatic hyphomycetes replaced terrestrial fungi on imported leaves, and Thornton's (1963) physiological studies showed that optimum growth temperatures of many aquatic hyphomycetes were lower than typical terrestrial fungi. Epicoccum nigrum, for example, grown on PDA had an optimum growth temperature of 250 (Godfrey, 1972). It is possible that in temperate regions terrestrial fungi become active in decomposition at higher water temperatures found, for example, in shallow lakes and ponds during summer months. Further studies are needed on their activity in aquatic habitats before they can be dismissed as unimportant in the processes of decomposition and energy flow.
REFERENCES
BARLOCHER, F. & KENDRICK, B. (1973). Fungi in the diet of Gammarus pseudolimnaeus (Amphipoda). Oikos 24, 295-3 00. BARLOCHER, F. & KENDRICK, B. (1974). Dynamics of the fungal population on leaves in a stream. Journal of Ecology 62, 761-791. BARLOCHER, F. & KENDRICK, B. (1975). Assimilation efficiency of Gammarus pseudolimnaeus (Amphipoda) feeding on fungal mycelium on autumn-shed leaves. Oikos 26, 55-59. CHAMIBR, A.-C. (1981). Pectinases in leaf degradation by aquatic hyphomycetes. Ph.D. Thesis, University of London. CHAMIBR, A.-C. & DIXON, P. A. (1982). Pectinases in leaf degradation by aquatic hyphomycetes. I. The field study. Oecologia 52, 109-115. FLANNIGAN, B. (1970). Degradation of arabinoxylan and carboxymethylcellulose by fungi isolated from barley kernels. Transactions of the British Mycological Society 55, 277-281. GoDFREY, B.E. S. (1972). A study ofthe microfungal flora of leaves of bracken, Pteridum aquilinum (L.) Kuhn, with reference to their role in the phyllosphere. Ph.D. Thesis, University of London. HANLON, R. D. G. (1981). Allochthonous plant litter as a source of organic material in an oligotrophic lake (Llyn Frongoch). Hydrobiologia So, 257-261.
Printed in Great Britain
Notes and brief articles KAUSHIK, N. K. & HYNES, H. B. N. (1968). Experimental study on the role of autumn shed leaves in aquatic environments. Journal of Ecology 56, 229-243. KAUSHIK, N. K. & HYNES, H. B. N. (1971). The fate of dead leaves that fall into streams. Archives fur Hydrobiologie 68, 465-515. MARcus, I. H. & WILLOUGHBY, L. G. (1978). Fungi as food for the aquatic invertebrate Asellus aquaticus. Transactions of the British Mycological Society 70, 143-146. PARK, D. (1982). Varicosporium as a competitive soil saprophyte. Transactions of the British Mycological Society 78, 33-41.
421
PETERSBN, R. C. & CUMMINS, K. W. (1974). Leaf processing in a woodland stream. FreshwaterBiology 4, 343-368. SUBBRKROPP, K. & KLuG, M. ]. (1976). Fungi and bacteria associated with leaves during processing in a woodland stream. Ecology 76, 707-719. SUBBRKROPP, K. & KLuG, M. ]. (1980). The maceration of deciduous leaf litter by aquatic hyphomycetes. Canadian Journal of Botany 58,1025-1031. THORNTON, D. R. (1963). The physiology and nutrition of some aquatic hyphomycetes. Journal of General Microbiology 33, 23-31.
WEIGHT LOSSES OF UNSTERILIZED FILTER-PAPER CAUSED BY COLONIES OF CEREAL FOOT-ROT FUNGI BY S. D. GARRETT
Botany School, University of Cambridge, Downing Street, Cambridge CBz lEA Mean dry-weight losses were recorded after 22 days at 20°C for single circles of Whatman NO.3 paper (7 cm diam), each inoculated with four 5 mm disks from fungal cultures on PD agar plates. Final size of colonie~ on unsterilized paper was determined partly by cellulolysis rate and partly by the intrinsic radial growth rate (measured on PD agar) of the fungal isolates; the correlation between colony size and the product of these two fungal factors was significant at the 1 % level. My first trial of unsterilized filter-paper as a to four on each paper circle, spaced equidistantly substrate for colonization by cereal foot-rot fungi round the margin of the circle but 1 em inside it, was concerned mainly with specification of the in- so as to give more room for the development of oculum potential needed for colonization (Garrett, fungal colonies. The number of paper plates for 1980). Unsterilized circles (7'0 em diam) of each treatment-series was increased to five to keep Whatman No. 3 paper, saturated with 2 ml the number of fungal colonies at 20. These were minerals solution, were inoculated with five disks measured, using a 5 x binocular magnifier, after the (5 mm diam) taken from behind the growing paper plates had been incubated in a water-bath margin of a colony on PD agar. The diameter of the incubator (to prevent drying) at 20±0'25° for 8,15 colony used for provision of inoculum disks did not and 22 days. The slow growth of these colonies on affect their inoculum potential in any of the fungal the paper plates was ascribed to the competition species except Fusarium culmorum (W.G.Sm.) from commensal bacteria for the sugars released by Sacco The unusually high metabolic rate of this fungal cellulolysis. This hypothesis was confirmed species causes its colonies to deplete PD agar later (Garrett, 1983), when addition of streptomycin beyond their margins of nutrients, so that inoculum sulphate at 150 mg 1-1 was found to remove this disks taken from inside the margin of a colony that growth restriction, so that the four fungal colonies had just filled the plate (F inocula) were unable to continued to grow until they nearly met. Adveninitiate colonies on unsterilized paper. This titious colonies of cellulolytic fungi, from prodifficulty was overcome by taking inoculum disks pagules either originally present on the paper or from inside the margin of colonies that had just deposited from the air, rarely developed on the half-filled their 8'5 cm diam plates (HF inocula). I paper circles, except in the presence of streptofound later increasing the depth of PD agar from mycin, when they were numerous. Although bacteria had thus been shown to 2' 5 to 3' 5 mm also increased inoculum potential of the disks sufficiently for them to produce colonies restrict fungal growth, it was not possible to say on the paper plates from F inocula (Garrett, 1983). whether all the bacteria involved were purely In the present study, HF and F inocula have again commensal, or whether some were cellulolytic. been compared, but this time with the agar plates Cellulolytic bacteria (mostly Cel/vibrio spp.) were found by Henis, Keller & Keyman (1961) to poured to the full depth of 3'5 mm. The number of inoculum disks was later reduced develop from soil crumbs placed on filter-paper Trans. Br. mycol, Soc. 81 (2), (1983)
Printed in Great Britain
N otes and brief articles REFERENC ES
CHAMIER, A.-C. (198o). Pect inases in leaf degradation by aqu atic hyphomycetes. Ph .D . Thesis, Un iversity of London, U.K. CHAMIER, A.-C . & DIXON, P. A. ( 1982 a). Pectinases in leaf degradation by aquatic hyph omycetes, I. The field study . The colonization-pattern of aquatic hyphomyceres on leaf packs in a Su rre y st ream . Oecologia 5z, 109-115. CHAMIER, A.-C. & DI XON, P . A. ( 1982 b). Pectinases in leaf degradation by aquatic hyph omycetes : the enzymes and leaf maceration. J ournal of General M icrobiology uS, 2469"-2483. DARVILL, A., McNEIL, M. , ALBI!RSHEIM, P. & DELMER, D . P. (1980). The primary cell walls of flowering plants. In The Plant Cell (ed. N . E. Tolbert), pp. 92-157. New York , U .S .A. : Academic Press .
DI XON, M . & WEBB, E. C. (1979). Enzym es, 3rd ed. Lond on : Longmans. EGGLISHAW, H . J. (1968). The quantitative relat ionsh ip between bottom fauna and plant detritus in streams of different calcium concentrations . J ournal of A pplied Ecology 5, 731-740. HANKIN, L., POINCELOT, R. P . & ANAGNOSTAKIS, S. L. (1976). Micro-organisms from comp osting leaves; abilit y to produce extracellular degradat ive enzymes. M icrobial Ecology z, 296-308. KAUSHIK, N. K . & HYNES, H . B. N . (1971). The fate of dead leaves that fall into streams. Archiv fur Hydrobiologie 68, 597-607 . REXOVA-BENKOVA, L. & MARKOVIC, O. (1976). Pectic enzymes. Advances in Carbohydrate Chemistry and Biochemistry 33, 323-385.
GROWTH OF TWO TERRESTRIAL MICROFUNGI ON SUBMERGED ALDER LEAVES BY B. E. S. GODFREY
Departm ent of Biological Sciences, City of London Polytechnic, Old Castle Stre et, London, EI 7N T Epicoccum nigrum and Cladosporium cladosporioides decomposed alder leaves and were cellulolytic in submerged cultures. It is now well established that allochthonous plant & Klug, 1976). Suberkropp & Klug (1976) debris forms an important energy source for certain emphasize the need to investigate the ir ability to freshwater ecosystems (Petersen & Cummins, decompose submerged plant material so that their 1974; Hanlon, 1981). Attention has mostly been contribution to the overall process of plant litter paid to leaf litter and it has been shown that man y decomposition in aquatic habitats can be assessed. different microfungi may be isolated from submerDuring a sur vey of microfungi on plant leaf litter ged leaves including aquatic hyphomycetes, as well in a small flooded gravel pit in southern England, as species normally associated with terrestrial Hesketh (pers. cornm.) frequently isolated Cladohabitats (Kaushik & Hynes, 1968, 1971; Barlocher sporium cladosporioides (Fres.) de Vries and Epicoc& Kendrick, 1974; Suberkropp & Klug, 1976; cum nigrum L ink. The work described here was Chamier & D ixon, 1982). It appears that certain undertaken to assess their ability to degrade leaves microfungi, particularly the aquatic hyphomycetes, of alder (A lnus glutinosa ), which often const itute a ' condition ' imported plant debris making it more major component of submerged plant debris in palatable and nutritious for detritevores (Barlocher streams and ponds. Freshly fallen alder leaves were collected in & Kendrick, 1973, 1975; Marcus & Willoughby, November 1978, air-dried and stored at 4 DC until 1978). Aquatic hyphomycetes appear to be the dominant needed. Before use the leaves were washed in colonizers of leaf debris (Kaushik & Hynes, 1971; running tap water for 48 h, dried to constant weight Barlocher & Kendrick, 1974) and are generally at 800 and then placed singly in 250 ern" conical considered to be the main agent s of decomposition. flasks charged with 100 ern" of a mineral salts Recent studies by Suberkropp & Klug (198o) and medium containing MgSO, . 5H 20 , 0'075 g ; Chamier (1981) have confirmed that some, at least, KH 2PO" 0'075 g; KCI 0'03 g ; Ca(N03)2.4H20 ; have enzymes capable of breaking down pect ins, distilled water 1 I. After sterilizing by autoclav ing cellulose and hemicellulose. Although the aquatic at 1210 for 15 min flasks were inoculated with hyphomycetes seem to dominate the mycoflora, eithe r a small tuft of mycelium taken from the edge some authors consider that the so-called terrestrial of a z-week-old culture of E. nigrum or 0' 5-1 '0 em" fungi , pre sent on the plant det ritus when it falls into of a spore suspension prepared from an 8- to water , may play some part in the decomposition ro-day-old culture of C. cladosporioides, both grown process (Barlocher & Kendrick, 1974; Suberkropp on potato dextrose agar (PDA). Cultures were Trans. B r. my col. S oc. 81 (2), (1983)
Prim ed in Great Britain
Notes and brief articles Table
1.
Mean percentage dry weight loss of alder leaves C. cladosporioides 26'2
Control Expt.l Exptv a
18'3 16'7
Expt·3
2S'3
Incubation time (weeks) 21 21 22
E.nigrum 43.6 37'6
30·8
In each experiment the means are significantly different at the 95 % level or better.
incubated in the dark at 16-18°. Five replicate flasks were inoculated for each fungus and uninoculated flasks provided controls. Three similar experiments were set up and after incubation for 21 or 22 weeks leaves were harvested and dried to constant weight at 80°. At the end of the experiments mycelial growth could be seen on the leaves in inoculated flasks. Both fungi caused a significant loss in weight compared with the untreated controls (Table 1). E. nigrum caused greater loss in weight than C. cladosporioides and it was also observed that leaves inoculated with E. nigrum were soft and limp compared with the uninoculated controls. In two subsequent experiments designed to monitor progressive weight loss over 4 months, leaves which had been soaked in running water for 48 h and then dried to constant weight at 80° were sterilized individually by exposure to gamma rays from a cobalt source for 78 h. The irradiated leaves
45 40
~ ~
oS
35 30
:EOIl 25
'" 20 ~
,I!',. . -to---f----f
15 10 5
4
12
8
16
Weeks Fig. 1. Loss in weight of Alnus glutinosa leaves inoculated with E. nigrum (e) compared with uninoculated controls (x). Each point is the mean of five replicates; confidence limits set at P = 0'05 . Trans. Br . mycol. Soc. 81 (2), (1983)
35
*.
------£
.-_ •• -
.._.I1
10 5
4
12
8
16
Weeks Fig. 2. Loss in weight of Alnus glutinosa leaves inoculated with C. cladosporioides
were introduced singly into sterilized 250 ern" conical flasks containing mineral salts solution, and inoculated as described above . Sterility was confirmed by plating out fragments of treated leaves on to PDA . Leaves were harvested at 4-week intervals and dried to constant weight 80°. Leaves lost weight rapidly during the first rhonth and continued to do so in the case of E. nigrum (Fig. 1) so that by the end of week 16 the inoculated leaves had lost significantly more weight than the controls. In the case of C. cladosporioides (Fig . 2) there was little further loss in weight beyond week 8, although by the end of the experiment the inoculated leaves weighed significantly less than the controls. These results confirm the observations in the previous experiments that both fungi can decompose submerged alder leaves but that E. nigrum is more active than C. cladosporioides. Further experiments were conducted to test the cellulolytic ability of C. cladosporioides and E. nigrum. Five replicate flasks were prepared for each fungus containing 100 em" of the mineral salts medium plus one oven-dried, pre-weighed
Printed in Great Britain
Notes and brief articles
420
Table 2. Mean percentage dry weight loss of filter paper disks
Expt.1 Expt.2 Expt·3
Control 3'4 1 0"38 2'59
C" cladosporioides
E. nigrum
Incubation time (weeks)
13"52
5 10 10
11"19 12"02
In each experiment the means are significantly different at the 95 % level or better.
Whatman No.1 filter disk (5"5 em diam). After sterilization at 1210 for 15 min the cooled flasks were inoculated with either C. cladosporioides or E. nigrum as described above. Cultures were incubated in the dark at 16-18 0 • The disks were harvested and dried to constant weight. Both species were found to utilize pure cellulose and to a similar extent. The observations indicate that these two terrestrial species have the potential to participate in the breakdown of leaf litter in water and are in general agreement with the results obtained by Barlocher & Kendrick (1974) on maple-leaf disks inoculated with an unspecified Cladosporium sp. Most of the soluble organic substances are rapidly leached from dead leaves (Kaushik & Hynes, 1971), leaving a framework consisting largely of cellulose, hemicellulose and lignin, and the main agents of decomposition will be those organisms able to produce the enzymes capable of degrading these materials. Both fungi tested here were shown to be capable of degrading pure cellulose (filter paper). Flannigan (1970), working on one strain of C. cladosporioides and five of E. nigrum, found that all produced xylanases while three strains of E. nigrum produced cellulase capable of reducing the viscosity of carboxymethylcellulose. Recently Park (1982) demonstrated that both C. cladosporioides and E. nigrum metabolized filter-paper cellulose and that E. nigrum was more active than C. cladosporioides. These observations support the results obtained in this study, where E. nigrum caused a greater weight loss in alder leaves than C. cladosporioides. The softened texture of the alder leaves after incubation with E. nigrum is further evidence of its ability to break down the structural tissues. The extensive weight loss in the controls as well as the inoculated leaves in the first week of the time-course experiments, even after soaking for 48 h, is probably due to leaching of water-soluble substances from the leaves. However, the overall loss in weight provides further evidence of the plant decomposing potential of both fungi. Thus it is evident that at least two members of the 'terrestrial' mycoflora commonly present on plant litter at the time of leaf fall can be active in Trans. Br. mycol. Soc. 81 (2), (1983)
decomposition under water. The question remains, however, whether they do, in practice, participate in the decomposition process under natural conditions. Barlocher & Kendrick (1974) showed that in streams at temperatures of 1-100 aquatic hyphomycetes replaced terrestrial fungi on imported leaves, and Thornton's (1963) physiological studies showed that optimum growth temperatures of many aquatic hyphomycetes were lower than typical terrestrial fungi. Epicoccum nigrum, for example, grown on PDA had an optimum growth temperature of 250 (Godfrey, 1972). It is possible that in temperate regions terrestrial fungi become active in decomposition at higher water temperatures found, for example, in shallow lakes and ponds during summer months. Further studies are needed on their activity in aquatic habitats before they can be dismissed as unimportant in the processes of decomposition and energy flow.
REFERENCES
BARLOCHER, F. & KENDRICK, B. (1973). Fungi in the diet of Gammarus pseudolimnaeus (Amphipoda). Oikos 24, 295-3 00. BARLOCHER, F. & KENDRICK, B. (1974). Dynamics of the fungal population on leaves in a stream. Journal of Ecology 62, 761-791. BARLOCHER, F. & KENDRICK, B. (1975). Assimilation efficiency of Gammarus pseudolimnaeus (Amphipoda) feeding on fungal mycelium on autumn-shed leaves. Oikos 26, 55-59. CHAMIBR, A.-C. (1981). Pectinases in leaf degradation by aquatic hyphomycetes. Ph.D. Thesis, University of London. CHAMIBR, A.-C. & DIXON, P. A. (1982). Pectinases in leaf degradation by aquatic hyphomycetes. I. The field study. Oecologia 52, 109-115. FLANNIGAN, B. (1970). Degradation of arabinoxylan and carboxymethylcellulose by fungi isolated from barley kernels. Transactions of the British Mycological Society 55, 277-281. GoDFREY, B.E. S. (1972). A study ofthe microfungal flora of leaves of bracken, Pteridum aquilinum (L.) Kuhn, with reference to their role in the phyllosphere. Ph.D. Thesis, University of London. HANLON, R. D. G. (1981). Allochthonous plant litter as a source of organic material in an oligotrophic lake (Llyn Frongoch). Hydrobiologia So, 257-261.
Printed in Great Britain
Notes and brief articles KAUSHIK, N. K. & HYNES, H. B. N. (1968). Experimental study on the role of autumn shed leaves in aquatic environments. Journal of Ecology 56, 229-243. KAUSHIK, N. K. & HYNES, H. B. N. (1971). The fate of dead leaves that fall into streams. Archives fur Hydrobiologie 68, 465-515. MARcus, I. H. & WILLOUGHBY, L. G. (1978). Fungi as food for the aquatic invertebrate Asellus aquaticus. Transactions of the British Mycological Society 70, 143-146. PARK, D. (1982). Varicosporium as a competitive soil saprophyte. Transactions of the British Mycological Society 78, 33-41.
421
PETERSBN, R. C. & CUMMINS, K. W. (1974). Leaf processing in a woodland stream. FreshwaterBiology 4, 343-368. SUBBRKROPP, K. & KLuG, M. ]. (1976). Fungi and bacteria associated with leaves during processing in a woodland stream. Ecology 76, 707-719. SUBBRKROPP, K. & KLuG, M. ]. (1980). The maceration of deciduous leaf litter by aquatic hyphomycetes. Canadian Journal of Botany 58,1025-1031. THORNTON, D. R. (1963). The physiology and nutrition of some aquatic hyphomycetes. Journal of General Microbiology 33, 23-31.
WEIGHT LOSSES OF UNSTERILIZED FILTER-PAPER CAUSED BY COLONIES OF CEREAL FOOT-ROT FUNGI BY S. D. GARRETT
Botany School, University of Cambridge, Downing Street, Cambridge CBz lEA Mean dry-weight losses were recorded after 22 days at 20°C for single circles of Whatman NO.3 paper (7 cm diam), each inoculated with four 5 mm disks from fungal cultures on PD agar plates. Final size of colonie~ on unsterilized paper was determined partly by cellulolysis rate and partly by the intrinsic radial growth rate (measured on PD agar) of the fungal isolates; the correlation between colony size and the product of these two fungal factors was significant at the 1 % level. My first trial of unsterilized filter-paper as a to four on each paper circle, spaced equidistantly substrate for colonization by cereal foot-rot fungi round the margin of the circle but 1 em inside it, was concerned mainly with specification of the in- so as to give more room for the development of oculum potential needed for colonization (Garrett, fungal colonies. The number of paper plates for 1980). Unsterilized circles (7'0 em diam) of each treatment-series was increased to five to keep Whatman No. 3 paper, saturated with 2 ml the number of fungal colonies at 20. These were minerals solution, were inoculated with five disks measured, using a 5 x binocular magnifier, after the (5 mm diam) taken from behind the growing paper plates had been incubated in a water-bath margin of a colony on PD agar. The diameter of the incubator (to prevent drying) at 20±0'25° for 8,15 colony used for provision of inoculum disks did not and 22 days. The slow growth of these colonies on affect their inoculum potential in any of the fungal the paper plates was ascribed to the competition species except Fusarium culmorum (W.G.Sm.) from commensal bacteria for the sugars released by Sacco The unusually high metabolic rate of this fungal cellulolysis. This hypothesis was confirmed species causes its colonies to deplete PD agar later (Garrett, 1983), when addition of streptomycin beyond their margins of nutrients, so that inoculum sulphate at 150 mg 1-1 was found to remove this disks taken from inside the margin of a colony that growth restriction, so that the four fungal colonies had just filled the plate (F inocula) were unable to continued to grow until they nearly met. Adveninitiate colonies on unsterilized paper. This titious colonies of cellulolytic fungi, from prodifficulty was overcome by taking inoculum disks pagules either originally present on the paper or from inside the margin of colonies that had just deposited from the air, rarely developed on the half-filled their 8'5 cm diam plates (HF inocula). I paper circles, except in the presence of streptofound later increasing the depth of PD agar from mycin, when they were numerous. Although bacteria had thus been shown to 2' 5 to 3' 5 mm also increased inoculum potential of the disks sufficiently for them to produce colonies restrict fungal growth, it was not possible to say on the paper plates from F inocula (Garrett, 1983). whether all the bacteria involved were purely In the present study, HF and F inocula have again commensal, or whether some were cellulolytic. been compared, but this time with the agar plates Cellulolytic bacteria (mostly Cel/vibrio spp.) were found by Henis, Keller & Keyman (1961) to poured to the full depth of 3'5 mm. The number of inoculum disks was later reduced develop from soil crumbs placed on filter-paper Trans. Br. mycol, Soc. 81 (2), (1983)
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