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Brazilian Journal of Botany

Print version ISSN 0100-8404On-line version ISSN 1806-9959

Revta. brasil. Bot. vol. 21 n. 3 São Paulo Dec. 1998

http://dx.doi.org/10.1590/S0100-84041998000300003 

Fungal succession on leaves of Alchornea triplinervia (Spreng.) Muell. Arg. submerged in a stream of an Atlantic Rainforest in the state of São Paulo, Brazil1 

 

IRACEMA HELENA SCHOENLEIN-CRUSIUS2  and ADAUTO IVO MILANEZ2

 

(recebido em 12/03/97; aceito em 01/04/98)

 

 

ABSTRACT - (Fungal succession on leaves of Alchornea triplinervia (Spreng.) Muell. Arg. submerged in a stream of an Atlantic Rainforest in the state of São Paulo, Brazil). Leaves of Alchornea triplinervia (Spreng.) Muell. Arg. were submerged in a stream in an Atlantic Rainforest in São Paulo state, Brazil, from July/1988 to June/1989 and from July/1989 to May/1990. Fungi were isolated by the leaf disks washing technique followed by plating on culture media and also by using baiting techniques (using substrates with chitin, keratin and cellulose), what resulted on 565 fungal registers corresponding to 81 taxa. The most common species found during this study of the fungal succession were Trichoderma viride Pers. ex S.F. Gray and Fusarium oxysporum Schlecht emend. Snyd. & Hans. (23 registers), Penicillium hirsutum Dierckx (21 registers), Fusarium solani (Mart.) Appel & Wollenw. emend. Snyd. & Hans. (17), followed by 14 registers of: Cylindrocladium scoparium Morgan, Triscelophorus monosporus Ingold and Polychytrium aggregatum Ajello. Although the monthly obtained mycota had been composed by species of different taxonomic groups, the fungal succession was defined by the initial presence of typical terrestrial leaf inhabiting fungi (mostly Deuteromycotina), followed by species of Mastigomycotina and Zygomycotina. Combining culture methods and baiting techniques, it was possible to verify the presence of terrestrial fungi on the decomposition of submerged leaves and the importance of zoosporic fungi in the fungal succession. This is the first paper about the fungal succession on the decomposition of leaves submerged in a lotic ecosystem in Brazil.

RESUMO - (Sucessão fúngica em folhas de Alchornea triplinervia (Spreng.) Muell. Arg. submersas em um riacho na Mata Atlântica no estado de São Paulo, Brasil). Folhas de Alchornea triplinervia (Spreng.) Muell. Arg. foram submersas em um riacho na Mata Atlântica no estado de São Paulo, Brasil, de julho de 1988 a junho de 1989 e de julho de 1989 a maio de 1990. Os fungos foram isolados pela técnica de lavagem de discos de folhas seguida por plaqueamento em meio de cultura, bem como pela técnica de iscagem (utilizando substratos com quitina, queratina e celulose), resultando em 565 registros de ocorrências de fungos, distribuídos em 81 táxons. Os fungos mais comuns durante a sucessão foram Trichoderma viride Pers. ex S.F. Gray e Fusarium oxysporum Schlecht emend. Snyd. & Hans. (23 registros), Penicillium hirsutum Dierckx (21 registros), Fusarium solani (Mart.) Appel & Wollenw. emend. Snyd. & Hans. (17), seguidos por 14 registros de Cylindrocladium scoparium Morgan, Triscelophorus monosporus Ingold e Polychytrium aggregatum Ajello. Embora a micota obtida mensalmente tenha sido composta por espécies de diferentes grupos taxonômicos, a sucessão fúngica foi definida pela presença inicial de fungos habitantes de folhas, tipicamente terrestres (na maioria Deuteromycotina), seguida por espécies de Mastigomycotina e Zygomycotina. Combinando métodos de cultivo e técnicas de iscagem, foi possível verificar a presença de fungos terrestres na decomposição de folhas submersas e a importância dos fungos zoospóricos na sucessão fúngica. Este é o primeiro trabalho sobre sucessão fúngica durante a decomposição de folhas submersas em ambiente lótico no Brasil.

Key words - Fungal succession, leaf decomposition, Atlantic Rainforest, aquatic system

 

 

Introduction

Due to their activity in the decomposition of a significative part of the allochthonous organic matter and a consequent important role as one of the main mechanisms for nutrient cycling, fungi have been considered the most efficient microorganisms, increasing the palatability of submerged substrates for shredders (Bärlocher & Kendrick 1974, Butler & Suberkropp 1986, Gessner & Chauvet 1994), justifying the importance of the knowledge of their occurrences, diversity and distribution patterns, especially in aquatic environments.

The usually diversified and competitive mycota present in the leaf tissues, before submergence, may include "autochthonous" fungi, that resist to drastic environmental changes and participate on further decomposition processes, until some of the native aquatic fungi are able to colonize and dominate the substrate (Park 1972). The sequential replacement of the fungal species may be strongly affected by the nutrient content of the substrates, but also by the competition abilities of each fungus. According to Garrett (1963) the success of the fungi to reach and colonize organic substrates may be mainly determined by their competitive saprophytic ability, expressed by fast mycelial growth, spores production, presence of an efficient enzymatic systems and tolerance to antibiotics. So, the occurrence of several fungal groups, each with specific competitive saprophytic abilities, during the decomposition of leaves may result in a process known as fungal succession (Frankland 1981).

The mycota associated to the decomposition of submerged leaves has been studied concerned to the diversity of aquatic Hyphomycetes comparing several kind of leaf species (Sridhar & Kaveriappa 1989; Gessner & Chauvet 1994) and different streams, particularly with the aim to verify the influence of the water chemistry on relationships between fungal activity and breakdown rates (Suberkropp & Chauvet 1995).

Although the occurrence of fungal succession during the decomposition of submerged leaves had been described, detailed studies about the subject are still scarce (Newell 1976, Davis & Winterbourn 1977, Puppi 1983, Gessner et al. 1993).

The first papers about fungal succession on submerged leaves in Brazil were concerned with the decomposition of Ficus microcarpa L.f. leaves in an artificial lake in the "Parque Estadual das Fontes do Ipiranga" (Schoenlein-Crusius & Milanez 1989) and leaves of Quercus robur L. leaves submerged in a lake in the municipality of "Itapecerica da Serra", both from São Paulo state (Schoenlein-Crusius et al. 1990). The results revealed the efficiency of the combination of isolation and baiting methods to obtain a representative mycota, and the participation of zoosporic fungi in the fungal succession.

The aim of this paper is to contribute for the knowledge about the diversity of fungi in the succession process during the decomposition of A. triplinervia leaves, submerged in a stream in the Atlantic Rainforest of Paranapiacaba, SP.

 

Material and methods

The present study was performed in the Atlantic Rainforest of the "Reserva Biológica do Alto da Serra de Paranapiacaba", which is located in the municipality of Santo André in São Paulo, approaching an area of 336 ha under the responsibility of the "Instituto de Botânica" in São Paulo, SP. Some considerations about the community structure, climatic conditions, sampling sites in the aquatic and terrestrial environment, as well as the isolation methods employed to obtain the fungi from the leaves were fully described in Schoenlein-Crusius & Milanez (1998). A brief summary about the sampling and isolation methods is presented: the experiment was conducted during two periods of time: August of 1988 to July of 1989 and August of 1989 to May of 1990. In July of 1988 and 1989 recently fallen leaves of A. triplinervia were taken from plastic collectors attached under the trees during one month. In the laboratory, the leaves were air dried (25-30oC), divided in samples of approximately 20 g and placed into 200 nylon net (1 mm diam. mesh) litter bags (20x20 cm). Forty litter bags were submerged at each of five collection points along the stream. The distance among the collection points was around 5 m, being three and two points respectively chosen for each site of the stream.

Fungi were isolated by the leaf disk washing technique (Pugh et al. 1972) followed by plating on four culture media: potato dextrose agar for saccharolytic fungi (Difco Manual 1972), starch agar for amilolytic fungi (Difco Manual 1972), cellulose agar for cellulolytic fungi (Eggins & Pugh 1962) and pectin agar for pectinolytic fungi. The last medium was composed by minimum mineral medium (Difco Manual 1972) plus commercial pectin (10 g/ liter). About twenty washed leaf disks were incubated in Petri dishes containing distilled sterilized water and baits: snake skin, shrimp shells, blond human hair, corn straw, cellophane, pollen of Pinus sp. and Sorghum sp. seeds to isolate zoosporic fungi (Beneke & Rogers 1962, Milanez 1984).

The fungi were isolated from the dry leaves in July of 1988 and in July of 1989 to provide knowledge about the composition of the mycota before submergence in the stream, as a startpoint to follow further changes of the successional fungal communities.

The colonies of Deuteromycotina, Zygomycotina and Ascomycotina that grew around the leaf disks were isolated after seven days of incubation (20-25oC), while the zoosporic fungi were observed after five days of incubation.

Current literature cited in Schoenlein-Crusius & Milanez (1998) was used to identify the fungal taxa at species level, whenever possible. After identification, the cultures were preserved by Castellani’s and lyophilization methods and stored in the Culture Collection of the Mycological Section of the Botanical Institute. Microscopical slides prepared with cotton blue and sealed with nail polish were also kept for observation.

 

Results and Discussion

A total of 81 taxa distributed in 565 registers were obtained (table 1), representing respectively: 50 species of Deuteromycotina (361 registers), 7 species of Zygomycotina (48 registers), 19 zoosporic fungi (133 registers) and 5 species of Ascomycotina (23 registers).

 

Table 1 - Fungal succession on A. triplinervia leaves submerged in a stream in the Atlantic Rainforest of Paranapiacaba, SP, from July/1988 to June/1989 and July/1989 to May/1990.

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The species of Deuteromycotina presented higher number of registers than the ones of Ascomycotina, Zygomycotina and Mastigomycotina (zoosporic fungi), what is very close to the results obtained for the leaves of Ficus microcarpa in an earlier study (Schoenlein-Crusius & Milanez 1989). Also in the leaves of Quercus robur the species of Deuteromycotina were predominant (Schoenlein-Crusius et al. 1990), in a similar way as occurred in the present paper. In the plant species mentioned above, the mycota present in the leaves before submergence remained in the substrates during a relatively long period of time, four to six months. Therefore, the results presented here are showing the adequacy of considering the autochthonous fungi, present in the recent fallen leaves as a startpoint mycota for the fungal succession in the aquatic environment.

On table 1 the fungi isolated from the submerged leaves were disposed according to their occurrences, following the fungal succession, since before the submergence of the leaves in the stream. So, the taxa registered in July of 1988 and July of 1989 were isolated from the leaves before the submergence. During the first period of the experiment, the highest number of fungal specimens was registered in January of 1989 (38 registers) and the lowest in August of 1988 (13 registers). During the second period, the highest number was registered in April of 1990 (40 registers) and the lowest in July of 1989 (10 registers), before the leaves were submerged in the stream.

The most common genera were Fusarium (11 registers), Trichoderma (6), Penicillium (5), Cladosporium (4) and Mucor (4). Among them, the following species presented the highest numbers: Trichoderma viride (23), Fusarium oxysporum (23) and Penicillium hirsutum (21).

Trichoderma viride, Fusarium oxysporum, Penicillium hirsutum, Alternaria alternata, Mucor hiemalis, Epicoccum purpurescens and Aspergillus clavatus were components of the mycota isolated from the leaves prior the submergence until intermediate stages of the decomposition (table 1). The resistance of autochthonous fungi to the environmental changes was often demonstrated for terrestrial (Hudson 1968) and aquatic habitat (Park 1972; Puppi 1983). Au & Hodgkiss (1992) verified that aquatic Hyphomycetes and "geofungi" showed a complementary sequence of dominance in winter and summer in a non polluted stream, whereas in high polluted sites, a dominance of the geofungi occurred during almost all time of the experiment. On the other hand, taking the ergosterol production of the fungi isolated from leaves, as an indicator for decomposition activity, the role of "geofungi" was considered inexpressive when compared with aquatic Hyphomycetes (Bärlocher et al. 1995). Considering the high diversity of the terrestrial fungi usually found in submerged substrates, the role of "geofungi" and of the zoosporic fungi (that do not produce ergosterol) in the decomposition of submerged substrates have to be stressed out in further studies.

Trichoderma viride (23 registers), Fusarium oxysporum (23), Penicillium hirsutum (21), Alternaria alternata (10), Mucor hiemalis (16), Epicoccum purpurascens (10), Aspergillus clavatus (13) and Fusarium graminearum (7) were isolated from the recently fallen leaves and were present even after the submergence of the substrate.

From the first month on, Aspergillus niger, Cladosporium sphaerospermum, Cylindrocladium scoparium, Colletotrichum orbiculare, Fusarium solani, Paecilomyces javanicus, Pestalotia clavata, and Rhizopus arrhizus were isolated. The occurrence of R. arrhizus, registered here, has been more connected with the soil than with the aquatic environment (Schipper 1978).

Acremonium strictum, Anguillospora crassa, Lunulospora curvula, Tetrachaetum elegans, Tripospermum sp., Triscelophorus monosporus and Verticillium fungicola were isolated from the thirth month on. These taxa have been frequently mentioned for many leaf species (Godeas 1985, Butler & Suberkropp 1986, Sridhar & Kaveriappa 1989).

According to Newton (1971), as soon as the leaves are submerged in the water, many species of aquatic Hyphomycetes are "attracted" to the substrate, taking their place as initial decomposers. Although the aquatic Hyphomycetes, as well as some zoosporic fungi may be considered initial decomposers, with high capacity to degrade cellulose and lignin compounds (Willoughby 1974), their presence in the leaves of A. triplinervia was registered only after two to three months of the succession (table 1), probably due to competitive interactions with the autochthonous mycota.

After the fourth month, Gliocladium roseum, Karlingia rosea, Microsphaeriopsis olivacea, Nectria haematococca and Nigrospora oryzae were isolated from the substrate. Trichoderma koningii and Verticillium lecanii were observed from the fifth month on. Cladosporium cladosporioides, C. oxysporum and Paecilomyces clavisporus were isolated from the next month on, together with many zoosporic fungi such as Achlya dubia, A. flagellata, A. radiosa, Cladochytrium replicatum, Dictyuchus sp., Karlingiomyces sp., Polychytrium aggregatum, Pythium sp., Rhizophlyctis sp., Saprolegnia ferax and Saprolegnia parasitica.

Karlingia rosea and Nowakowskiella elegans have been considered cellulolytic fungi, while Polychytrium aggregatum has demonstrated a high affinity with keratin substrates (Willoughby 1974).

The presence of the zoosporic fungi in the decomposing leaves, resulted in an increase of the total number of registers, from 16 in December of 1988 to 38 in January of 1989, during the first period of the experiment (table 1). Their participation in the fungal succession seems to have changed significantly the distribution patterns of the decomposing mycota. In the leaves of A. triplinervia the diversity of zoosporic fungi was higher than of the aquatic Hyphomycetes (table 1). The informations about the diversity, environmental limitations and decomposing activity of the aquatic Hyphomycetes in the Atlantic Rainforest are still few to explain or to compare the results obtained here with several others, in which the aquatic Hyphomycetes are usually dominant, active and highly diversified (Bärlocher & Kendrick 1974, Sridhar & Kaveriappa 1989, Gessner et al. 1993, Gessner & Chauvet 1994). The failure of many species to grow on culture media and the necessity to use baiting techniques to detect their presence on the substrates, make the study of the activity of zoosporic fungi very difficult, justifying their absence in the studies mentioned above.

Aspergillus alutaceus, Cladosporium herbarum, Gelasinospora cerealis and Rhizophydium elyensis were isolated since the seventh month of decomposition.

From the eighth and ninth months on, Catenophlyctis variabilis, Fusarium lateritium, Mucor hiemalis f. silvaticus, M. circinelloides, Rhizophydium stipitatum and Trichoderma hamatum were intensively isolated.

Chaetomium globosum, Mucor circinelloides f. janssenii, Phoma chrysantemicola, Rhizopus oryzae, Rhizophydium sphaerotheca, Rhizidium chitinophylum, and Trichoderma pseudokoningii were observed in the last month of the experiment.

The number of fungal species and the total number of registers increased in function of the time of decomposition of the leaves. However, the fungi present at the beginning of the succession showed higher register numbers than those at the end of the process (table 1). Once again, the dominance of terrestrial fungi on the submerged substrate may justify these results. It seems possible that after some time the conditions of the leaves allow the establishment of a more diversified mycota.

Curvularia brachyspora, Fusarium clamydosporum, F. heterosporum, F. moniliforme, F. nivale, F. poae, F. sambucinum, Nowakowskiella elegans, Paecilomyces variottii, Penicillium aurantiobrunneum, P. brevicompactum, P. coriophylum, P. oxalicum, Phlyctochytrium sp., Phoma jolyana, Rhizophydium chitinophylum, Talaromyces flavus, Trichoderma harzianum, T. longibrachiatum and Zygorrhynchus moelleri showed an irregular distribution pattern during the decomposition period.

The fungal succession (table 1) may not be well defined by the sequential occurrence of taxonomic groups such as was stated in the studies of Newell (1976) and Frankland (1981), but some tendencies may be pointed out from the results. The presence of typical terrestrial fungi belonging to Deuteromycotina, seems to be connected with the initial stages of the decomposition of the leaves, whereas the presence of species of Zygomycotina may be expected at the end of the process. Zoosporic fungi and aquatic Hyphomycetes showed a tendency to occur in an intermediate phases of the succession.

The methods used to isolate the fungi may be carefully chosen to allow the obtaintion of a representative mycota. The combination of plating methods and baiting techniques confirmed to be useful to obtain a diversified mycota from leaves submerged in a stream of an Atlantic Rainforest.

 

Acknowledgment - The authors would like to express their gratitude to the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil, for partial financial support and to Dra. Maria Auxiliadora de Queiroz Cavalcanti from the Universidade Federal de Pernambuco and Dr. José Aires Ventura from the Empresa Capixaba de Pesquisa (EMCAPA) for their help in the identification of the fungi.

 

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1.Part of the Doctor’s Thesis of the first author.

2. Instituto de Botânica, Caixa Postal 4005, 01061-970 São Paulo, SP, Brazil.

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