Aquatic Hyphomycetes Research Articles

Reproduction of aquatic hyphomycetes at low concentrations of Ca2+, Zn2+, Cu2+, and Cd2+

Maple leaf disks were conditioned in a stream for three weeks and then aerated for 2 d in distilled water to induce fungal sporulation. The release of aquatic hyphomycete spores increased when the water was supplemented with low concentrations of Ca(2+) (5 µg/L), Zn(2+) (2.5 µg/L), Cu(2+) (0.5 µg/L), or Cd(2+) (0.125 µg/L). Higher supplement concentrations inhibited sporulation. Over the concentration range used, the sporulation response was generally best described by a quadratic regression, suggesting a biphasic or hormetic response. A similar pattern was found with the number of fungal species as the dependent variable. Anguillospora filiformis and Anguillospora longissima were generally least inhibited by metal supplements, and Ca(2+) was the least and Cd(2+) the most toxic metal. Combinations of metals had a more severe effect on fungal sporulation than predicted from addition of the effects of the metals in isolation. The biological significance of the hormetic response is unclear; however, acknowledging it is clearly relevant for establishing guidelines or recommendations in toxicology.

Aquatic hyphomycetes and other water-borne fungi in Hungary.

Aquatic hyphomycetes and other water-borne fungi in Hungary.

Fungi in freshwaters: ecology, physiology and biochemical potential

Research on freshwater fungi has concentrated on their role in plant litter decomposition in streams. Higher fungi dominate over bacteria in terms of biomass, production and enzymatic substrate degradation. Microscopy-based studies suggest the prevalence of aquatic hyphomycetes, characterized by tetraradiate or sigmoid spores. Molecular studies have consistently demonstrated the presence of other fungal groups, whose contributions to decomposition are largely unknown. Molecular methods will allow quantification of these and other microorganisms. The ability of aquatic hyphomycetes to withstand or mitigate anthropogenic stresses is becoming increasingly important. Metal avoidance and tolerance in freshwater fungi implicate a sophisticated network of mechanisms involving external and intracellular detoxification. Examining adaptive responses under metal stress will unravel the dynamics of biochemical processes and their ecological consequences. Freshwater fungi can metabolize organic xenobiotics. For many such compounds, terrestrial fungal activity is characterized by cometabolic biotransformations involving initial attack by intracellular and extracellular oxidative enzymes, further metabolization of the primary oxidation products via conjugate formation and a considerable versatility as to the range of metabolized pollutants. The same capabilities occur in freshwater fungi. This suggests a largely ignored role of these organisms in attenuating pollutant loads in freshwaters and their potential use in environmental biotechnology.

Experimental shading alters leaf litter breakdown in streams of contrasting riparian canopy cover

Summary 1. Headwater stream ecosystems are primarily heterotrophic, with allochthonous organic matter being the dominant energy. However, sunlight indirectly influences ecosystem structure and functioning, affecting microbial and invertebrate consumers and, ultimately, leaf litter breakdown. We tested the effects of artificial shading on litter breakdown rates in an open-canopy stream (high ambient light) and a closed-canopy stream (low ambient light). We further examined the responses of invertebrate shredders and aquatic hyphomycetes to shading to disentangle the underlying effects of light availability on litter breakdown. 2. Litter breakdown was substantially slower for both fast-decomposing (alder, Alnus glutinosa) and slow-decomposing (beech, Fagus sylvatica) leaf litters in artificially shaded stream reaches relative to control (no artificial shading) reaches, regardless of stream type (open or closed canopy). 3. Shredder densities were higher on A. glutinosa than on F. sylvatica litter, and shading had a greater effect on reducing shredder densities associated with A. glutinosa than those associated with F. sylvatica litter in both stream types. Fungal biomass was also negatively affected by shading. Results suggest that the effects of light availability on litter breakdown rates are mediated by resource quality and consumer density. 4. Results from feeding experiments, where A. glutinosa litter incubated under ambient light or artificial shade was offered to the shredder Gammarus fossarum, suggest that experimental shading and riparian canopy openness influenced litter palatability interactively. Rates of litter consumption by G. fossarum were decreased by experimental shading in the open-canopy stream only. 5. The results suggest that even small variations in light availability in streams can mediate substantial within-stream heterogeneity in litter breakdown. This study provides further evidence that changes in riparian vegetation, and thus light availability, influence organic matter processing in heterotrophic stream ecosystems through multiple trophic levels.

Canopy fungi (“terrestrial aquatic hyphomycetes”) from twigs of living evergreen and deciduous trees in Hungary

Canopy fungi (“terrestrial aquatic hyphomycetes”) from twigs of living evergreen and deciduous trees in Hungary

Future increase in temperature more than decrease in litter quality can affect microbial litter decomposition in streams

The predicted increase in atmospheric CO(2) concentration for this century is expected to lead to increases in temperature and changes in litter quality that can affect small woodland streams, where water temperature is usually low and allochthonous organic matter constitutes the basis of the food web. We have assessed the individual and interactive effect of water temperature (5 and 10°C) and alder litter quality produced under ambient CO(2) levels (ambient litter) or under CO(2) concentrations predicted for 2050 (elevated litter) on litter decomposition and on fungal activity and assemblage structure. Litter decomposition rates and fungal respiration rates were significantly faster at 10 than at 5°C, but they were not affected by litter quality. Litter quality affected mycelial biomass accrual at 5 but not at 10°C, while increases in temperature stimulated biomass accrual on ambient but not on elevated litter. A similar pattern was observed for conidial production. All variables were stimulated on elevated litter at 10°C (future scenario) compared with ambient litter at 5°C (present scenario), but interactions between temperature and litter quality were additive. Temperature was the factor that most strongly affected the structure of aquatic hyphomycete assemblages. Our results indicate that if future increases in atmospheric CO(2) lead to only slight modifications in litter quality, the litter decomposition and fungal activities and community structure will be strongly controlled by increased water temperature. This may have serious consequences for aquatic systems as faster litter decomposition may lead to food depletion for higher trophic levels.

Diversity of lignicolous and Ingoldian fungi on woody litter from the River Kali (Western Ghats, India)

Three hundred and sixty woody litter samples naturally deposited in a stream and dammed section of the River Kali in southwest India were assessed for the diversity of lignicolous fungi (ascomycetes and anamorphic fungi) via damp chamber incubation and aquatic hyphomycetes (Ingoldian fungi) via bubble chamber incubation. Fifty-six fungal taxa were recorded with the highest of 47 taxa in the stream and 34 taxa in the dam. Twenty-five taxa were common to both sites. The core group (≥10%) comprised one ascomycete (Massarina australiensis), two anamorphic taxa (Acrogenospora sphaerocephala and Sporoschisma saccardoi) and 11 Ingoldian fungi (Anguillospora crassa, A. longissima, Clavariana aquatica, Cylindrocarpon sp., Flagellospora curvula, F. penicillioides, Lunulospora curvula, L. cymbiformis, Lunulospora sp., Triscelophorus acuminatus, T. monosporus). The species richness, average taxa per wood sample, richness of core group fungi and fungal diversity were higher in the Kaiga stream than in the Kadra dam. Species abundance curves showed higher frequency of occurrence of fungi in the stream than in the dam woody litter. The rarefaction indices of fungal species against number of wood samples revealed similar pattern of ascomycetes in both locations, while the richness of anamorphic and Ingoldian taxa was higher in the stream than in the dam. The anamorph/teleomorph ratio ranged between 2.4:1 (Kadra dam) and 3.3:1 (Kaiga stream), which is higher than the ratios reported from other geographical locations (0.7:1−2:1). This study reconfirmed that the method of incubation influences the assessment of fungal communities in woody litter and that Ingoldian fungi also constitute an important component of woody litter.

Leaf litter breakdown in Mediterranean streams: effect of dissolved inorganic nutrients

Agricultural runoff and urban activities can increase the inputs of nitrogen (N) and phosphorus (P), into headwater streams, leading to eutrophication and thus substantially affecting the structure and functions of benthic communities. A high P concentration in water stimulates the activity of heterotrophic microorganisms associated with leaf litter and, hence, influences decomposition rates and the availability of detrital resources for macroinvertebrates. Litter breakdown of alder (Alnus glutinosa) leaves enclosed in coarse mesh bags was studied in five low-order Mediterranean streams with different trophic status defined by their soluble reactive phosphorus (SRP) concentrations. Decomposition rates differed significantly between these streams and increased with the eutrophication gradient, but these differences were not always related to the availability of P in water. Leaf mass loss was directly correlated with shredder density, but macroinvertebrate density and diversity were not related to P availability in water, and ammonium concentration had a negative effect on macroinvertebrate diversity and shredder relative abundance. A significantly positive effect of nitrate concentration in water on aquatic hyphomycete sporulation rates was observed, but there also was a negative effect of % ammonium on dissolved inorganic nitrogen (DIN). The predominantly available ionic form of DIN could thus affect the structure of the aquatic hyphomycete community. These results suggest that the response of litter decomposition to eutrophication in forested headwater streams is strongly influenced by local stream characteristics and by the nature of nutrient pollution.

Optimal sample size for species composition evaluation of leaf litter in mountain streambeds

Aquatic hyphomycetes or Ingoldian fungi are the major decomposers of leaf litter in temperate aquatic ecosystems. Role of leaf litter quality in structuring hyphomycete communities is intensively discussed among hydrobiologists. Therefore, an adequate sampling strategy of the leaf litter is essential in this field. The present paper aims analysing the appropriate sample size of leaf litter with various diversity and evenness combinations taken from streambeds in the temperate deciduous forest zone.Leaf litter in the streambed was sampled at four stream sections of two tributaries of the Morgo stream in the Borzsony Mts, Hungary. The tributaries differed in water chemistry, altitude and riparian vegetation. To analyse species number-sample size relations, species saturation diagrams were drawn and statistically evaluated.Results showed that: (1) a sample size of 500 leaves sufficiently describes the species composition of leaf litter taken from streambeds in the temperate forest zone, in cases of low diversity forest stands and high diversity forest stands coupled with high evenness; and (2) for forest sites with high diversity coupled with low evenness values a litter sample composed by 800-1000 leaves is advised to investigate to achieve satisfactory estimation of the species composition of leaf litter.The sampling methods described in this paper are proposed for studies where estimation of leaf litter composition is required to understand the available substrate quality for litter decomposing organisms.

Do the tropical freshwater fishes feed on aquatic fungi?

Consumption and processing of allochthonous plant litter by fishes is more common in tropical than temperate streams and rivers. Therefore, aquatic hyphomycetes in water (filtration), leaf litter (bubble chamber incubation), and fecal pellets (direct observation and inoculation to sterile leaf litter) of three dominant fishes belonging to the family Cyprinidae (Aplocheilus lineatus, Puntius filamentosus, and Rasbora daniconius) in two locations of the River Kali of the Western Ghats, India, were evaluated during postmonsoon season. Spores of 14 and 9 species of aquatic hyphomycetes were recovered on filtering water samples of Kaiga stream and Kadra dam with equal number of spores (32 spores · 100 mL−1) and high Shannon diversity in Kaiga stream. In a bubble chamber incubation of leaf litter, 16 and 9 species were recovered from Kaiga stream and Kadra dam with high spore output (1122 versus 324 spores per mg dry mass) and high Shannon diversity in Kaiga stream. Both direct and indirect methods of examination of fecal pellets of fishes revealed more species in Kaiga stream than Kadra dam (4–7 versus 1–4 species). The spore release in leaf litter incubated with fecal pellets ranged from 2.3 to 98 spores·mg−1·d−1 with the highest Aplocheilus lineatus in Kaiga stream; while in Kadra dam, it was from 0.02 to 22.9 spores·mg−1·d−1 with the highest in Puntius filamentosus. The Shannon diversity of aquatic hyphomycetes was high in fecal pellets of Aplocheilus lineatus of Kaiga stream and Rasbora daniconius of Kadra dam. The top-ranked five species of aquatic hyphomycetes differed in water, leaf litter, and fish fecal pellets; however, Triscelophorus konajensis was common for all. All five top-ranked species of aquatic hyphomycetes in feces produced multicelled spores; thus, they were likely to have a better chance of viability through gut passage than single-celled spores. Preferential feeding, fungi in gut and feces, and survival and dissemination of spores by invertebrates and fishes with reference to aquatic hyphomycetes were discussed.

Effects of 4-n-nonylphenol on aquatic hyphomycetes

We measured the removal of 4-n-nonylphenol (between 50 and 500 μg L −1) from an aqueous solution with or without linden and oak leaf disks. More 4-n-NP was removed when the leaves were first exposed for 3 weeks in a stream, which allowed colonization by aquatic hyphomycetes. The response of fungal sporulation rates from beech, linden, maple and oak leaves to increasing levels of 4-n-NP was complex. Linear regressions were non-significant, arguing against a no-threshold model. The response at the lowest concentration (50 μg L −1) was between 7% (beech) and 67% (maple) higher than in the absence of 4-n-NP, however, the difference was not significant. The number of sporulating species of aquatic hyphomycetes was significantly higher at the lowest concentration than in the control treatment without 4-n-NP. The composition of the fungal community was affected by leaf species but not by 4-n-NP concentration. The results suggest the presence of a weak hormeotic effect. The known ability of aquatic hyphomycetes and other fungi to degrade nonylphenols and related substances, combined with fungal resilience in their presence, makes decaying leaves potential candidates for bioremediation.

Population genetics of the aquatic fungus Tetracladium marchalianum over space and time.

Aquatic hyphomycete fungi are fundamental mediators of energy flow and nutrient spiraling in rivers. These microscopic fungi are primarily dispersed in river currents, undergo substantial annual fluctuations in abundance, and reproduce either predominantly or exclusively asexually. These aspects of aquatic hyphomycete biology are expected to influence levels and distributions of genetic diversity over both spatial and temporal scales. In this study, we investigated the spatiotemporal distribution of genotypic diversity in the representative aquatic hyphomycete Tetracladium marchalianum. We sampled populations of this fungus from seven sites, three sites each in two rivers in Illinois, USA, and one site in a Wisconsin river, USA, and repeatedly sampled one population over two years to track population genetic parameters through two seasonal cycles. The resulting fungal isolates (N = 391) were genotyped at eight polymorphic microsatellite loci. In spite of seasonal reductions in the abundance of this species, genotypic diversity was consistently very high and allele frequencies remarkably stable over time. Likewise, genotypic diversity was very high at all sites. Genetic differentiation was only observed between the most distant rivers (∼450 km). Clear evidence that T. marchalianum reproduces sexually in nature was not observed. Additionally, we used phylogenetic analysis of partial β-tubulin gene sequences to confirm that the fungal isolates studied here represent a single species. These results suggest that populations of T. marchalianum may be very large and highly connected at local scales. We speculate that large population sizes and colonization of alternate substrates in both terrestrial and aquatic environments may effectively buffer the aquatic populations from in-stream population fluctuations and facilitate stability in allele frequencies over time. These data also suggest that overland dispersal is more important for structuring populations of T. marchalianum over geographic scales than expected.

Decomposition of native leaf litter by aquatic hyphomycetes in an alpine stream

Despite the recognised significance of hyphomycetes in the degradation of leaf litter in streams, few studies have been carried out in alpine environments and none in Australian alpine streams. We hypothesised that the fungal communities responsible for leaf decomposition would change over immersion time, and would respond differently at different sites and on different types of vegetation. Leaf bags containing Epacris glacialis (F. Muell.), Eucalyptus pauciflora (Sieber ex. Spreng) and Eucalyptus delegatensis (R.T. Baker) were deployed at different sites in a stream in the Victorian Alpine National Park, south-eastern Australia. Leaf colonisation was delayed for 2 weeks and decay constants for E. pauciflora and E. delegatensis were 0.004–0.005 and 0.006 respectively. Maximum fungal biomass on leaves was similar to that in previous published studies, whereas sporulation rates were two or three orders of magnitude lower, indicating a reduced reproductive effort. Sporulation and DNA-based studies combined showed that fungal communities on the decomposing leaf material changed over time and exhibited significant preferences for leaf type and study site. We have shown that aquatic hyphomycetes can degrade physically tough leaves of Australian alpine plant species, potentially contributing to pathways for particulate carbon to enter alpine-stream food webs.

Synergistic effects of water temperature and dissolved nutrients on litter decomposition and associated fungi

In woodland streams, the decomposition of allochthonous organic matter constitutes a fundamental ecosystem process, where aquatic hyphomycetes play a pivotal role. It is therefore greatly affected by water temperature and nutrient concentrations. The individual effects of these factors on the decomposition of litter have been studied previously. However, in the climate warming scenario predicted for this century, water temperature and nutrient concentrations are expected to increase simultaneously, and their combined effects on litter decomposition and associated biological activity remains unevaluated. In this study, we addressed the individual and combined effects of water temperature (three levels) and nutrient concentrations (two levels) on the decomposition of alder leaves and associated aquatic hyphomycetes in microcosms. Decomposition rates across treatments varied between 0.0041 day−1 at 5 °C and low nutrient level and 0.0100 day−1 at 15 °C and high nutrient level. The stimulation of biological variables at high nutrients and temperatures indicates that nutrient enrichment of streams might have a higher stimulatory effect on fungal performance and decomposition rates under a warming scenario than at present. The stimulation of fungal biomass and sporulation with increasing temperature at both nutrient levels shows that increases in water temperature might enhance fungal growth and reproduction in both oligotrophic and eutrophic streams. The stimulation of fungal respiration and litter decomposition with increasing temperature at high nutrients indicates that stimulation of carbon mineralization will probably occur at eutrophied streams, while oligotrophic conditions seem to be ‘protected’ from warming. All biological variables were stimulated when both factors increased, as a result of synergistic interactions between factors. Increased water temperature and nutrient level also affected the structure of aquatic hyphomycete assemblages. It is plausible that if water quality of presently eutrophied streams is improved, the potential stimulatory effects of future increases in water temperature on aquatic biota and processes might be mitigated.

Effects of Cadmium and Phenanthrene Mixtures on Aquatic Fungi and Microbially Mediated Leaf Litter Decomposition

Urbanization and industrial activities have contributed to widespread contamination by metals and polycyclic aromatic hydrocarbons, but the combined effects of these toxics on aquatic biota and processes are poorly understood. We examined the effects of cadmium (Cd) and phenanthrene on the activity and diversity of fungi associated with decomposing leaf litter in streams. Leaves of Alnus glutinosa were immersed for 10days in an unpolluted low-order stream in northwest Portugal to allow microbial colonization. Leaves were then exposed in microcosms for 14days to Cd (0.06-4.5mgL(-1)) and phenanthrene (0.2mgL(-1)) either alone or in mixture. A total of 19 aquatic hyphomycete species were found sporulating on leaves during the whole study. The dominant species was Articulospora tetracladia, followed by Alatospora pulchella, Clavatospora longibrachiata, and Tetrachaetum elegans. Exposure to Cd and phenanthrene decreased the contribution of A. tetracladia to the total conidial production, whereas it increased that of A. pulchella. Fungal diversity, assessed as denaturing gradient gel electrophoresis fingerprinting or conidial morphology, was decreased by the exposure to Cd and/or phenanthrene. Moreover, increased Cd concentrations decreased leaf decomposition and fungal reproduction but did not inhibit fungal biomass production. Exposure to phenanthrene potentiated the negative effects of Cd on fungal diversity and activity, suggesting that the co-occurrence of these stressors may pose additional risk to aquatic biodiversity and stream ecosystem functioning.

Issues of anamorphic fungi

At the time when there is a move towards the acceptance of one name for one biological fungal species, Fungal Diversity documents the importance of anamorphic fungi with a special issue devoted to them. The present issue comprises 13 papers devoted to various topics concerning the anamorphic fungi with contributions on phylogeny, chemistry, ecology, post harvest importance, molecular detection and descriptions of some plant pathogens. The first paper is a review of the biogeography and phylogeography of Fusarium. This important paper questions several trends in the understanding of this important genus which causes a wide variety of plant diseases, produces a number of mycotoxins and is becoming increasingly recognized as a significant human pathogen. The authors look at several examples where surveys of non agro-systems question the present understanding of this extraordinary genus and must be read. The second paper is also a review of the chemical and bioactive producing capabilities of the remarkable genus Pestalotiopsis. This mostly endophytic genus is especially productive with regard to the accumulation of a diverse array of mostly bioactive compounds. More than 130 different compounds with antifungal, antimicrobial, and antitumor activities have been isolated from various species of this amazing genus. The third and fourth papers deal with post harvest topics. Colletotrichum gloeosporioides was previously reported to be the casual agent of anthracnose of most tropical fruits. This taxon, however, was recently epitypified and has been shown to be a species complex. A molecular study of isolates from Laos and Thailand causing anthracnose of eight tropical fruits shows that species other than C. gloeosporioides are responsible for anthracnose of most tropical fruits. This astounding result illustrates an urgent need to carry out research on re-inventory of tropical plant pathogens and should result in an unprecedented increase in phytopathogen research. Thirty one species belonging to 17 fungal genera were found to be associated with sorghum grain samples imported to the Kingdom of Saudi Arabia. These anamorphic fungi are important post harvest organisms producing important mycotoxins. The papers recommends that rigorous quarantine and healthy storage conditions should be undertaken to minimize fungal contamination and prevent further hazard to human and animal health. Papers five to seven deal with assessing fungal biodiversity from environmental samples using molecular analysis. Sette et al. profiled the fungal community structure found in a Brazilian energy transmission tower with signs of corrosion and/or biofilm formation using cloning (ITS-rRNA gene libraries), a culture-dependent technique. A total of 31 isolates comprising ten filamentous fungi and four yeasts were recovered from enrichment cultures showing the usefulness of this method. Klaubauf et al. were also successfully able to use RFLP and sequence analysis of clone libraries of the partial ITS/LSU-region as a culture-independent method to survey fungal diversity in four arable soils and one grassland in Lower Austria. Seena et al. show that aquatic hyphomycetes can be directly K. D. Hyde (*) School of Science, Mae Fah Luang University, Tasud, Chiang Rai 57100, Thailand e-mail: kdhyde2@gmail.com

Molecular approaches promise a deeper and broader understanding of the evolutionary ecology of aquatic hyphomycetes

AbstractResearch on aquatic hyphomycetes has been dominated by process-oriented approaches. The main objectives have been accurate estimates of fungal biomass and production and measuring fungal impact on plant litter decomposition. In some cases, these estimates have been complemented by community assessments based on spore counts. Many other ecological and evolutionary topics, commonly studied in macroorganisms, were largely inaccessible, in part because of the low morphological complexity of fungal structures and the near impossibility of identifying them in situ unless attached to propagules. Molecular methods rely on extraction, amplification (polymerase chain reaction) and characterization (denaturing gradient gel electrophoresis, digitized fluorescent restriction-fragment length polymorphism, sequencing) of deoxyribonucleic acid (DNA), which occurs in all cells regardless of their reproductive status. Molecular methods allow more comprehensive characterizations of fungal diversity and evolution. En...

Contamination by uranium mine drainages affects fungal growth and interactions between fungal species and strains

The presence of aquatic hyphomycetes has been reported for several heavy metal-contaminated waters. Tolerance probably is one adaptation to coping with heavy metals. To help clarify this issue strains of two species of aquatic hyphomycetes (Tricladium splendens Ingold and Varicosporium elodeae Kegel) were isolated from a reference stream and a stream contaminated with heavy metals and grown on malt extract agar prepared with reference and contaminated water to characterize colony morphology, growth rate, growth inhibition and interaction among species and strains. In V. elodeae the morphology of colonies differed between strains. Colony diameter increased linearly over time with growth rates being lower for strains isolated from contaminated than from reference streams (mostly for V. elodeae). Strains from the contaminated stream grew faster in medium prepared with contaminated water than in medium prepared with reference water, while for strains from the reference stream there was no significant difference in growth rates on the two media. In interacting isolates radial growth toward the opposing colony was generally lower than toward the dish edge. Percentage growth inhibition was higher for isolates in intraspecific interactions (13–37%) than in interspecific interactions (3–27%). However differences in growth inhibition experienced by interacting isolates were observed only in three cases out of 16. The difference between the percentage inhibition caused and experienced by a given isolate was highest in interactions involving isolates with distinct growth rates. Our results suggest that strains from the reference stream tolerate heavy metals while strains from the contaminated stream seem to be adapted to contaminated waters. We hypothesize that in natural environments fungal species-specific limits of tolerance to metal contamination might determine an abrupt or gradual response of the original fungal community to mine pollution giving origin to a poorer fungal community dominated by adapted strains with distinct functional efficiency.

Early stages of leaf decomposition are mediated by aquatic fungi in the hyporheic zone of woodland streams

Summary1. Leaf litter constitutes the major source of organic matter and energy in woodland stream ecosystems. A substantial part of leaf litter entering running waters may be buried in the streambed as a consequence of flooding and sediment movement. While decomposition of leaf litter in surface waters is relatively well understood, its fate when incorporated into river sediments, as well as the involvement of invertebrate and fungal decomposers in such conditions, remain poorly documented.2. We tested experimentally the hypotheses that the small interstices of the sediment restrict the access of the largest shredders to buried organic matter without compromising that of aquatic hyphomycetes and that fungal decomposers in the hyporheic zone, at least partly, compensate for the role of invertebrate detritivores in the benthic zone.3. Alder leaves were introduced in a stream either buried in the sediment (hyporheic), buried after 2 weeks of exposure at the sediment surface (benthic‐hyporheic), or exposed at the sediment surface for the entire experiment (benthic). Leaf decomposition was markedly faster on the streambed surface than in the two other treatments (2.1‐ and 2.8‐fold faster than in the benthic‐hyporheic and hyporheic treatments, respectively).4. Fungal assemblages were generally less diverse in the hyporheic habitat with a few species tending to be relatively favoured by such conditions. Both fungal biomass and sporulation rates were reduced in the hyporheic treatment, with the leaves subject to the benthic‐hyporheic treatment exhibiting an intermediate pattern. The initial 2‐week stage in the benthic habitat shaped the fungal assemblages, even for leaves later subjected to the hyporheic conditions.5. The abundance and biomass of shredders drastically decreased with burial, except for Leuctra spp., which increased and was by far the most common leaf‐associated taxon in the hyporheic zone. Leuctra spp. was one of the rare shredder taxa displaying morphological characteristics that increased performance within the limited space of sediment interstices.6. The carbon budgets indicated that the relative contributions of the two main decomposers, shredders and fungi, varied considerably depending on the location within the streambed. While the shredder biomass represented almost 50% of the initial carbon transformed after 80 days in the benthic treatment, its contribution was <0.3% in the hyporheic one and 2.0% in the combined benthic‐hyporheic treatment. In contrast, mycelial and conidial production in the permanently hyporheic environment accounted for 12% of leaf mass loss, i.e. 2–3 times more than in the two other conditions. These results suggest that the role of fungi is particularly important in the hyporheic zone.7. Our findings indicate that burial within the substratum reduces the litter breakdown rate by limiting the access of both invertebrate and fungal decomposers to leaves. As a consequence, the hyporheic zone may be an important region of organic matter storage in woodland streams and serve as a fungal inoculum reservoir contributing to further dispersal. Through the temporary retention of litter by burial, the hyporheic zone must play a significant role in the carbon metabolism and overall functioning of headwater stream ecosystems.

DNA barcoding of fungi: a case study using ITS sequences for identifying aquatic hyphomycete species

Aquatic hyphomycetes are a polyphyletic group of fungi that play a crucial role in organic matter turnover in streams. They have been traditionally identified based on the morphology of conidia collected in stream water or obtained from leaves colonized in nature upon aeration in the laboratory. Therefore, species identification is limited by our ability to induce conidium production and to establish pure cultures. Conidial shapes are believed to be the result of convergent evolution, so similar conidia may be produced by different conidiogenesis processes, which may prevent unambiguous identification. Currently, a great effort in fungal taxonomy is being made at introducing a set of criteria based on comparisons of selected nucleotide sequences instead of or in addition to phenotypic characters. We examined the suitability of ITS1-5.8S-ITS2 rRNA gene region or its subregions (ITS1 and ITS2) to identify aquatic hyphomycetes, by sequencing and comparing these regions in 94 fungal isolates belonging to 19 species collected in Portuguese streams with different environmental conditions during 8 years. Sequences of ITS1, ITS2 and ITS1-5.8S-ITS2 rRNA genes of the Portuguese isolates of aquatic hyphomycetes and those from the GenBank exhibited taxonomic cohesiveness, the isolates grouped with their respective species but all Tricladium species did not group within the Tricladium genus. Cohesiveness was not observed between isolates with respect to location, condition of stream or date of collection. Evolutionary divergences (ITS1-5.8S-ITS2 sequences; Kimura 2-parameter distance) between con-specific isolates were shallow and a deep divergence between species was generally observed. The NJ trees based on ITS1 or ITS2 rRNA gene sequences had lower statistical support for some internal nodes, we therefore propose ITS1-5.8S-ITS2 rRNA gene as barcode for identifying species of aquatic hyphomycetes.