Stream Litter Research Articles

Direct and indirect effects of zinc oxide and titanium dioxide nanoparticles on the decomposition of leaf litter in streams.

As the production of metallic nanoparticles has grown, it is important to assess their impacts on structural and functional components of ecosystems. We investigated the effects of zinc and titanium nanoparticles on leaf decomposition in freshwater habitats. We hypothesized that nanoparticles would inhibit the growth and activity of microbial communities leading to decreased decomposition rates. We also hypothesized that under natural light, the nanoparticles would produce reactive oxygen species that could potentially accelerate decomposition. In the lab, whole Ficus vasta leaves were placed in containers holding one liter of stream water and exposed to either 0, 1, 10 or 100 mg/L of ZnO or TiO2 nanoparticles for six weeks (referred to as Exp. 1). We measured leaf mass loss, microbial metabolism, and bacterial density at 2, 4, and 6 weeks. In a second experiment (referred to as Exp. 2), we measured the effects of light and 10 and 100 mg/L ZnO or TiO2 nanoparticles on leaf mass loss, bacterial density and the bacterial and fungal community diversity over a 2 week period. In Experiment 1, mass loss was significantly reduced at 10 and 100 mg/L after 6 weeks and bacterial density decreased at 100 mg/L. In Experiment 2, there was no effect of ZnO nanoparticles on leaf mass loss, but TiO2 nanoparticles significantly reduced mass loss in the dark but not in the light. One possible explanation is that release of reactive oxygen species by the TiO2 nanoparticles in the light may have increased the rate of leaf decomposition. Bacterial and fungal diversity was highest in the dark, but nanoparticles did not reduce overall diversity.

Inventory of chytrid diversity in two temporary forest ponds using a multiphasic approach

ABSTRACTFood webs in temporary forest ponds are driven by decomposition of terrestrial inputs. Chytrid fungi are important components of the fungal community, degrading leaf litter in streams reliant on terrestrial inputs and in lake ecosystems where they may stabilize the food web. However, little is known about chytrid fungi in temporary forest ponds. We inventoried the chytrid diversity present in two temporary forest ponds via light microscopy of baited samples and ion semiconductor (Ion Torrent) sequencing of environmental DNA. We quantified trends of chytrid alpha and beta diversity as a function of spatial and temporal factors. A total of 59 chytrid taxa were detected throughout the study. Beta diversity exhibited variation across the sampled months for both the entire fungal community as well as for chytrids alone. Shifts in community composition were also apparent, although diversity metrics and composition patterns did not meet adjusted P values. The results of this study highlight the diversity of chytrid fungi in temporary forest ponds and the need for further studies on the spatial and temporal dynamics of chytrid species.

Relations of interannual differences in stream litter breakdown with discharge: bioassessment implications

AbstractEcosystem‐level processes are increasingly used by researchers and managers as indicators of ecological integrity for bioassessment, particularly in streams. However, processes like litter breakdown integrate multiple mechanistic pathways, which can vary differentially even under natural, unimpacted conditions. In particular, weather‐driven hydrologic variations may strongly influence invertebrate shredder feeding and physical abrasion, inducing high natural variability of litter breakdown rates, which may obscure the effects of anthropogenic disturbances. Yet, such variability is rarely assessed to refine benchmarks of ecological status. Here, we quantified how interannual hydrologic differences contributed to the spatio‐temporal variability of litter breakdown rate and its components (fragmentation, λF; and dissolution and microbial decomposition, λm), in low‐order unimpacted, perennial streams across three climatically similar regions in temperate Canada. We measured litter breakdown rates in coarse (5 or 10 mm; kc)‐ and fine‐mesh (0.5 mm; kf) leaf bags during fall for 2–4 yr and used variance partitioning to disentangle the variation of kc, λF, and λm, as explained by hydrologic indices (during and prior to leaf bag incubation), decomposer‐related variables, and water chemistry. Contrary to our hypotheses, interannual hydrologic variability was unrelated to λF, and poorly predicted λm and kc within regions. Within‐region spatial (i.e., across sites in a year) and temporal (across years at a site) differences in kc approximated or exceeded the range of natural variability suggested to characterize reference conditions by a popular bioassessment framework. Accordingly, we recommend site‐ and region‐specific modifications of benchmarks for reference conditions that account for interannual variability, while cautioning about their potential non‐stationarity under climate change. Composite parameters such as kc/kf and λF/λm were substantially more variable across sites, and hence are not robust assessment parameters. As the range of natural variability of litter breakdown revealed in this study can overlap with the average impacts of certain anthropogenic disturbances (e.g., nutrient enrichment) on this parameter reported by previous research, we emphasize the need to include other structural and functional indicators to ensure comprehensive stream bioassessments.

Hydrological contingency: drying history affects aquatic microbial decomposition

Climate change, land use intensification, and water abstraction magnify the frequency and severity of droughts but also result in totally unnatural hydrological patterns. Longer and more severe droughts slow down organic matter decomposition, whereas the effect of drying history, i.e. the specific sequence of different conditions to which organic matter is exposed, has seldom been addressed. Drying history could have important consequences for microbial communities colonizing and decomposing leaf litter in streams given the rapid fluctuations in microbial composition and processes. We studied whether the effects of drought-related impacts (stagnation, drying and both) on microbial activity and leaf litter decomposition are affected by the timing when peak stress (stagnation or drying) occurs, and whether the effect of the drying history is consistent among the three different stress types. In laboratory microcosms, we recreated areas with flowing water (aerated water), isolated pools with stagnant water (non-aerated water) and dry beds (dry microcosms). Combining these conditions and their sequence, we created nine treatments (ten with the control) differing in stress type (stagnation, drying, both) and timing of peak stress (early, middle, late), and measured fungal biomass, sporulation, microbial respiration, and microbial decomposition of alder leaf disks. The effects of drought-related stress conditions were not consistent among response variables. However, disturbances were systematically more detrimental to decomposition in early stages, resulting in a lower fungal biomass and activity, and reduced microbial litter decomposition. These results suggest that the effects of stress on decomposition-associated variables depend not only on the intensity of the stress, but also on its timing, with early stress and its legacy effects having greatest impact on leaf litter decomposition.

Distinct Trophic Specializations Affect How Phytophthora ramorum and Clade 6 Phytophthora spp. Colonize and Persist on Umbellularia californica Leaves in Streams.

Phytophthora spp. are regularly recovered from streams but their ecology in aquatic environments is not well understood. Phytophthora ramorum, invasive in California forests, persists in streams at times when sporulation in the canopy is absent, suggesting that it reproduces in the water. Streams are also inhabited by resident, clade 6 Phytophthora spp., believed to be primarily saprotrophic. We conducted experiments to determine whether differences of trophic specialization exist between these two taxa, and investigated how this may affect their survival and competition on stream leaf litter. P. ramorum effectively colonized fresh (live) rhododendron leaves but not those killed by freezing or drying, whereas clade 6 species colonized all leaf types. However, both taxa were recovered from naturally occurring California bay leaf litter in streams. In stream experiments, P. ramorum colonized bay leaves rapidly at the onset; however, colonization was quickly succeeded by clade 6 species. Nevertheless, both taxa persisted in leaves over 16 weeks. Our results confirm that clade 6 Phytophthora spp. are competent saprotrophs and, though P. ramorum could not colonize dead tissue, early colonization of suitable litter allowed it to survive at a low level in decomposing leaves.

Does the developmental stage and composition of riparian forest stand affect ecosystem functioning in streams?

A common watershed restoration practice to improve water quality and stream ecosystem functions and services is replanting riparian corridors with plant species that may differ from those of natural communities. This restoration practice may have consequences on the aquatic ecosystem processes because organisms obtain energy from leaf litter inputs of the riparian zones. Leaf litter decomposition in streams is a vital ecosystem-level process, which depends on the activity of microorganisms and invertebrates. In the current study, we examined whether the type and developmental stage of riparian forest affect stream ecosystem functioning. We selected three widespread tree species in the Northwest Portugal, namely alder (Alnus glutinosa (L.) Gaertn.), oak (Quercus robur L.) and eucalyptus (Eucalyptus globulus Labill.) and conducted stream litter decomposition experiments with leaf litter from trees differing in developmental stage to assess leaf mass loss, fungal and invertebrate biomass and diversity. Both type and developmental stage of riparian stand significantly affected leaf mass loss, biomass of fungi and benthic invertebrates, sporulation of fungi, and abundance of invertebrates. However, only developmental stage of the riparian stand had an impact on the richness and diversity of fungi, whereas invertebrate diversity and richness was influenced by both stage and type classes.Overall our study provides the novel information that stream ecosystem processes are dictated not only by the composition but also by the developmental stage of the riparian stand. Moreover, this study provides an insight into how by altering riparian forest community composition through restoration practices may have an impact on a key ecosystem process and may have implications for successfully implementing future management strategies.

Temperature modulates AgNP impacts on microbial decomposer activity

Silver nanoparticles (AgNP)s can have toxic effects on aquatic species and compromise important ecosystem processes. AgNP impacts have been the focus of much research, but their effects under different environmental contexts, such as the increase in global temperature are difficult to predict. The aim of this study was to evaluate the interactive effects of AgNPs and temperature on the activity and diversity of microbial decomposers of plant litter in streams. Litter-associated microbial communities were exposed in microcosms to increased concentrations of AgNPs (50 to 75000μgL−1) and AgNO3 (5 to 7500μgL−1) and kept for 21days at 10°C, 16°C and 23°C. Effects of AgNPs and AgNO3 were assessed based on leaf mass loss and litter-associated microbial communities by measuring microbial diversity, the activity of fungal extracellular enzymes, and fungal biomass and reproduction. Increase in temperature stimulated leaf mass loss, but not fungal biomass and reproduction. Increased AgNP and AgNO3 concentrations inhibited fungal reproduction and diversity, particularly at 23°C. Activities of the extracellular enzymes phenol oxidase and β-glucosidase were generally higher at 23°C. Microbial communities were mainly structured by AgNP and AgNO3 concentrations more than by temperature. The negative effects of nano and ionic Ag on microbial activity were more pronounced at 10 and 23°C. The behavior of AgNPs was more related to water physical and chemical characteristics (pH) than to temperature. Results highlight the importance of considering different environmental scenarios when examining NP toxicity to freshwater biota and ecosystem processes.

Plastic litter in streams: The behavioral archaeology of a pervasive environmental problem

Plastic deposition in hydrological systems is a pervasive problem at all geographic scales from loci of pollution to global ocean circulation. Much attention has been devoted to plastic deposition in marine contexts, but little is known about inputs of plastics into local hydrological systems, such as streams. Attempts to prevent plastic litter must incorporate the role of people's behaviors, so we employ a behavioral archaeological framework to distinguish between various cultural inputs (e.g., littering) and noncultural forces (e.g., stream transport and wind) that affect litter patterns on the landscape. Four sites with varying cultural uses were surveyed monthly for eight months along a creek in Texas, and analysis of the data included chi-square and Kruskal Wallis tests, and abundance indices comparing material types across sites. We found that sites have drastically different distributions in plastic litter, and these patterns appear to align with the cultural uses (hiking, fishing, roadway) and presence or absence of noncultural forces at each site. This information can be used to inform efforts to reduce littering at these and potentially other locations with similar characteristics. This study illustrates that an archaeological framework provides an efficient and accurate way to generate local data on littering behaviors.

河川上流における落葉枝リターの時空間分布 : 底生動物の侵入定着の観点から( 河川における粒状有機物の移動と水生生物による利用-河川上流から沿岸海域における各場の特性と共通点)

河川上流における落葉枝リターの時空間分布 : 底生動物の侵入定着の観点から( 河川における粒状有機物の移動と水生生物による利用-河川上流から沿岸海域における各場の特性と共通点)

How do physicochemical properties influence the toxicity of silver nanoparticles on freshwater decomposers of plant litter in streams?

AgNP physicochemical properties may affect AgNP toxicity, but their effects on plant litter decomposition and the species driving this key ecosystem process in freshwaters have been poorly investigated. We assessed the impacts of AgNPs with different size and surface coating (100nm PVP (polyvinylpyrrolidone)-dispersant, 50–60nm and 35nm uncoated) on freshwater decomposers of leaf litter by exposing leaf associated microbial assemblages to increasing concentrations of AgNPs (up to 200mgL−1) and of AgNO3 (up to 25mgL−1). We further conducted a feeding preference experiment with a common invertebrate shredder, Limnephilus sp., which was allowed to feed on microbially-colonized leaves previously exposed to AgNPs and AgNO3. Leaf decomposition and microbial activity and diversity were inhibited when exposed to increased concentrations of 100nm AgNPs (≥25mgL−1), while microbial activity was stimulated by exposure to 35nm AgNPs (≥100mgL−1). Invertebrate shredders preferred leaves exposed to 35nm AgNPs (25mgL−1) and avoided leaves exposed to AgNO3 (≥2mgL−1). Results from the characterization of AgNPs by dynamic light scattering revealed that AgNps with PVP-dispersant were more stable than the uncoated AgNPs. Our results highlight the importance of considering the physicochemical properties of NPs when assessing their toxicity to litter decomposers in freshwaters.

Replacement of native forests by conifer plantations affects fungal decomposer community structure but not litter decomposition in Atlantic island streams

Forest change occurs worldwide, especially on islands where space is a limiting factor for human activities. The replacement of diverse native forests by tree monocultures and subsequent changes in litter input characteristics can have strong effects on stream communities and processes. Aquatic decomposers and litter decomposition can be particularly sensitive to forest change due to their dependence on terrestrial litter supply and on litter characteristics. However, studies addressing the effects of forest changes, and conifer plantations in particular, on stream litter decomposition and associated decomposers are scarce. Here, we assessed the effects of the replacement of native laurel forests in São Miguel island, Azores archipelago, by commercial conifer plantations (Cryptomeria japonica (L. f.) D. Don) on litter decomposition and associated fungal decomposers. Leaves of the native broadleaf tree Ilex perado Aiton and conifer needles were enclosed in mesh bags and incubated in three streams flowing through conifer plantations and three streams flowing through native laurel forests in winter 2015 for determination of litter decomposition rates, and aquatic hyphomycete community structure and reproductive activity (one stream per type). Aquatic hyphomycete communities’ structure strongly differed between native and conifer streams as a result from differences in the total number of species recorded (higher in the native stream), species identity (only 10 species, out of 26, were common to both streams) and species evenness (higher in the native stream). These differences in communities between streams likely result from changes in litter inputs characteristics between native and conifer streams and from aquatic hyphomycetes having substrate preferences. Differences in aquatic hyphomycete communities were not accompanied by differences in litter decomposition rates between native and conifer streams, which likely results from functional redundancy between decomposer communities and suggests that community structure and function may not always be tightly coupled. Litter decomposition rates did not differ between native and conifer species because I. perado leaves were tough and had a tick waxy cuticle, which may have limited microbial development, as for the conifer needles. Thus, the replacement of native laurel forests by conifer plantations did not affect litter decomposition in Azorean streams likely because litter is recalcitrant and decomposition is driven by microbes. However, changes in aquatic hyphomycete communities arriving from forest change may have unpredictable effects in case of additional environmental change. Hence, to prevent unwanted effects of changes in microbial communities, a riparian buffer of native vegetation should be maintained in conifer plantations.

Effects of aeration, sediment grain size and burial on stream litter breakdown and consumer performance: a microcosm study

Turbulence and aeration are reduced in many streams during low-flow periods as a consequence of drought or water abstraction, thus affecting invertebrate interactions and pivotal ecosystem processes such as the breakdown of organic matter (OM). These effects can be larger in the hyporheic zone (HZ), the ecotone connecting the surface stream and groundwater, especially when fine sediments reduce hydraulic conductivity. In addition, OM breakdown in the HZ could depend on the availability of OM in the benthic zone (BZ), because the latter would not only be a more accessible, and thus preferred, food resource, but also more easily scoured downstream. In a laboratory microcosm experiment of 28 days duration, we manipulated aeration, sediment size and location of OM (either all buried or half buried with half on the surface, simulating the HZ and BZ respectively). Six mayfly (Habroleptoides) individuals and four stonefly (Capnioneura) individuals were enclosed in each microcosm and the consumption of OM was measured. Lack of aeration reduced oxygen saturation from 94 to 66%, reducing OM consumption particularly on the surface, in contrast with our expectations. As hypothesised, the availability of surface OM significantly reduced invertebrate consumption of buried OM. Habroleptoides performed better than Capnioneura, especially in fine sediments. The results suggest that reduced turbulence can affect invertebrate trophic interactions as well as the decomposition of OM, depending on sediment grain size and the location of OM.

Identification of growing bacteria during litter decomposition in freshwater through H218O quantitative stable isotope probing.

Identification of microorganisms that facilitate the cycling of nutrients in freshwater is paramount to understanding how these ecosystems function. Here, we identify growing aquatic bacteria using H218O quantitative stable isotope probing. During 8 day incubations in 97 atom % H218O, 54% of the taxa grew. The most abundant phyla among growing taxa were Proteobacteria (45%), Bacteroidetes (30%) and Firmicutes (10%). Taxa differed in isotopic enrichment, reflecting variation in DNA replication of bacterial populations. At the class level, the highest atom fraction excess was observed for OPB41 and δ-Proteobacteria. There was no linear relationship between 18 O incorporation and abundance of taxa. δ-Proteobacteria and OPB41 were not abundant, yet the DNA of both taxa was highly enriched in 18 O. Bacteriodetes, in contrast, were abundant but not highly enriched. Our study shows that a large proportion of the bacterial taxa found on decomposing leaf litter grew slowly, and several low abundance taxa were highly enriched. These findings indicating that rare organisms may be important for the decomposition of leaf litter in streams, and that quantitative stable isotope probing with H218O can be used to advance our understanding of microorganisms in freshwater by identifying species that are growing in complex communities.

Fallout volume and litter type affect 137Cs concentration difference in litter between forest and stream environments

It is important to understand the changes in the 137Cs concentration in litter through leaching when considering that 137Cs is transferred from basal food resources to animals in forested streams. We found that the difference of 137Cs activity concentration in litter between forest and stream was associated with both litter type and 137Cs fallout volume around Fukushima, Japan. The 137Cs activity concentrations in the litter of evergreen conifers tended to be greater than those in the litter of broad-leaved deciduous trees because of the absence of deciduous leaves during the fallout period in March 2011. Moreover, 137Cs activity concentrations in forest litter were greater with respect to the 137Cs fallout volume. The 137Cs activity concentrations in stream litter were much lower than those in forest litter when those in forest litter were higher. The 137Cs leaching patterns indicated that the differences in 137Cs activity concentration between forest and stream litter could change with changes in both fallout volume and litter type. Because litter is an important basal food resource in the food webs of both forests and streams, the 137Cs concentration gradient reflects to possible 137Cs transfer from lower to higher trophic animals. Our findings will improve our understanding of the spatial heterogeneity and variability of 137Cs concentrations in animals resident to the contaminated landscape.

Ethanol and phenanthrene increase the biomass of fungal assemblages and decrease plant litter decomposition in streams

Fungi, particularly aquatic hyphomycetes, have been recognized as playing a dominant role in microbial decomposition of plant litter in streams. In this study, we used a microcosm experiment with different levels of fungal diversity (species number and identity) using monocultures and combinations with up to five aquatic hyphomycete species (Articulospora tetracladia, Tricladium splendens, Heliscus submersus, Tetrachaetum elegans and Flagellospora curta) to assess the effects of ethanol and phenanthrene on three functional measures: plant litter decomposition, fungal biomass accrual and reproduction. Alder leaves were conditioned by fungi for 7days and then were exposed to phenanthrene (1mgL−1) dissolved in ethanol (0.1% final concentration) or ethanol (at the concentration used to solubilise phenanthrene) for further 24days. Exposure to ethanol alone or in combination with phenanthrene decreased leaf decomposition and fungal reproduction, but increased fungal biomass produced. All aspects of fungal activity varied with species number. Fungal activity in polycultures was generally higher than that expected from the sum of the weighted performances of participating species in monoculture, suggesting complementarity between species. However, the activity of fungi in polycultures did not exceed the activity of the most productive species either in the absence or presence of ethanol alone or with phenanthrene.

Effects of land use on the structure and function of leaf‐litter microbial communities in boreal streams

Summary Microbial communities associated with leaf litter in streams provide key ecosystem services through the cycling of energy and nutrients that can be influenced by environmental factors. We examined the effects of land use on leaf‐litter microbial communities in boreal streams by comparing the structural (i.e. fungal and bacterial biomass and community composition by next generation sequencing) and functional (i.e. decomposition, and extracellular enzyme activities) characteristics of the microbial communities. Streams draining watersheds with histories of fire, logging, industrial‐mining and urban watershed activity were compared to reference streams. The most severely disturbed industrial and industrial‐urban streams had the lowest rates of microbial litter decomposition, greatly decreased fungal biomass and lacked the ubiquitous bacterial genera Pseudomonas, and Amantichitinum. Hydrolase activity was lowered in all streams with a history of disturbance, with potential adverse effects on energy and nutrient cycling. Our findings demonstrate that the microbial cycling of energy and nutrients in the boreal aquatic ecosystem is affected by land‐use disturbance and illustrate the excellent potential of using microbial communities to track the effects of watershed disturbance and restoration efforts on boreal shield aquatic ecosystems.

Copper and zinc affect the activity of plasma membrane H+-ATPase and thiol content in aquatic fungi.

Aquatic hyphomycetes are the major microbial decomposers of plant litter in streams. We selected three aquatic hyphomycete species with different abilities to tolerate, adsorb and accumulate copper and zinc, and we investigated the effects of these metals on H+-ATPase activity as well as on the levels of thiol (SH)-containing compounds. Before metal exposure, the species isolated from a metal-polluted stream (Heliscus submersus and Flagellospora curta) had higher levels of thiol compounds than the species isolated from a clean stream (Varicosporium elodeae). However, V. elodeae rapidly increased the levels of thiols after metal exposure, emphasizing the importance of these compounds in fungal survival under metal stress. The highest amounts of metals adsorbed to fungal mycelia were found in the most tolerant species to each metal, i.e. in H. submersus exposed to copper and in V. elodeae exposed to zinc. Short-term (10 min) exposure to copper completely inhibited the activity of H+-ATPase of H. submersus and V. elodeae, whilst zinc only led to a similar effect on H. submersus. However, at longer exposure times (8 days) the most metal-tolerant species exhibited increased H+-ATPase activities, suggesting that the plasma membrane proton pump may be involved in the acclimation of aquatic hyphomycetes to metals.

Different cesium-137 transfers to forest and stream ecosystems

Understanding the mechanisms of 137Cs movement across different ecosystems is crucial for projecting the environmental impact and management of nuclear contamination events. Here, we report differential movement of 137Cs in adjacent forest and stream ecosystems. The food webs of the forest and stream ecosystems in our study were similar, in that they were both dominated by detrital-based food webs and the basal energy source was terrestrial litter. However, the concentration of 137Cs in stream litter was significantly lower than in forest litter, the result of 137Cs leaching from litter in stream water. The difference in 137Cs concentrations between the two types of litter was reflected in the 137Cs concentrations in the animal community. While the importance of 137Cs fallout and the associated transfer to food webs has been well studied, research has been primarily limited to cases in a single ecosystem. Our results indicate that there are differences in the flow of 137Cs through terrestrial and aquatic ecosystems, and that 137Cs concentrations are reduced in both basal food resources and higher trophic animals in aquatic systems, where primary production is subsidized by a neighboring terrestrial ecosystem.

Nutrient enrichment alters the magnitude and timing of fungal, bacterial, and detritivore contributions to litter breakdown

Microbial decomposers and metazoan detritivores rely on and affect processing rates of detrital C in streams. Nutrient enrichment can affect the biomass of both groups, but we lack a quantitative understanding of how these groups affect breakdown rates of C under elevated nutrient conditions. We quantified the relative contribution of decomposers (fungi, bacteria) and detritivores (shredders) to breakdown rates in a reference vs a nutrient-enriched stream. We measured breakdown rates and litter-associated shredder, fungal, and bacterial biomass on Rhododendron maximum L. and Acer rubrum L. and modeled the contribution of these groups over the decay sequence for R. maximum and for a single time period for A. rubrum. We used published metabolic parameters for fungi and bacteria under high- and low-nutrient conditions and shredder feeding rates based on organisms and leaf litter from our study area. Breakdown rates of both litter types were higher (∼4–5×) in the treatment than reference stream and were associated with large changes in biomass of fungi, bacteria, and shredders. Changes in microbial metabolic parameters (growth rate, growth efficiency) affected estimates of mass loss. Fungal and shredder contributions were roughly equivalent and greater than bacterial contributions under reference and treatment conditions, but nutrient enrichment accelerated the colonization sequence of fungi and shredders, and shredders had relatively greater effects on mass loss in later stages of breakdown. Our results suggest facilitation of detritivores by decomposers and large combined effects on breakdown with nutrient enrichment. Decomposer contributions could exceed those of detritivores with changes in microbial metabolic rates. Large increases in breakdown rates could be attributed to biotic response to nutrient enrichment, are sensitive to microbial metabolic rates, and have the potential to alter residence times of litter in streams.

Microscopy- or DNA-based analyses: Which methodology gives a truer picture of stream-dwelling decomposer fungal diversity?

Abstract We assessed aquatic hyphomycete diversity in autumn and spring on oak leaves decomposing in five streams along a gradient of eutrophication in the Northwest of Portugal. Diversity was assessed through microscopy-based (identification by spore morphology) and DNA-based techniques (Denaturing Gradient Gel Electrophoresis and 454 pyrosequencing). Pyrosequencing revealed five times greater diversity than DGGE. About 21% of all aquatic hyphomycete species were exclusively detected by pyrosequencing and 26% exclusively by spore identification. In some streams, more than half of the recorded species would have remained undetected if we had relied only on spore identification. Nevertheless, in spring aquatic hyphomycete diversity was higher based on spore identification, probably because many species occurring in this season are not yet connected to ITS barcodes in genetic databases. Pyrosequencing was a powerful tool for revealing aquatic hyphomycete diversity on decomposing plant litter in streams and we strongly encourage researchers to continue the effort in barcoding fungal species.