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The extensive use of nanometal-based products increases the chance of their release into aquatic environments, raising the question whether they can pose a risk to aquatic biota and the associated ecological processes. Aquatic microbes, namely fungi and bacteria, play a key role in forested streams by decomposing plant litter from terrestrial vegetation. Here, we investigated the effects of nanocopper oxide and nanosilver on leaf litter decomposition by aquatic microbes, and the results were compared with the impacts of their ionic precursors. Alder leaves were immersed in a stream of Northwest Portugal to allow microbial colonization before being exposed in microcosms to increased nominal concentrations of nanometals (CuO, 100, 200 and 500 ppm; Ag, 100 and 300 ppm) and ionic metals (Cu(2+) in CuCl(2), 10, 20 and 30 ppm; Ag(+) in AgNO(3), 5 and 20 ppm) for 21 days. Results showed that rates of leaf decomposition decreased with exposure to nano- and ionic metals. Nano- and ionic metals inhibited bacterial biomass (from 68.6% to 96.5% of control) more than fungal biomass (from 28.5% to 82.9% of control). The exposure to increased concentrations of nano- and ionic metals decreased fungal sporulation rates from 91.0% to 99.4%. These effects were accompanied by shifts in the structure of fungal and bacterial communities based on DNA fingerprints and fungal spore morphology. The impacts of metal nanoparticles on leaf decomposition by aquatic microbes were less pronounced compared to their ionic forms, despite metal ions were applied at one order of magnitude lower concentrations. Overall, results indicate that the increased release of nanometals to the environment may affect aquatic microbial communities with impacts on organic matter decomposition in streams.

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1. The hyporheic zone of a permanent first-order stream was divided into a treatment and a control section using a 1 m deep sheet-metal barrier. During a 4-month pre-treatment period, water temperatures in two transects of the two sections were not different. Upon heating, the water temperature in the treatment transect increased by an average of 4.3°C over values in the control transect. 2. Eleven bimonthly core samples were taken from a treatment and a control transect, and recovered CPOM was classified as twigs, wood, grass, roots, cedar and deciduous leaves. 3. In both transects, twigs were the most common and deciduous leaves the least common substrates. The number of leaf fragments declined significantly in the heat-treated transect. 4. Diversity and frequencies of occurrence of aquatic hyphomycetes were highest on leaves and lowest on grass and wood. On leaves, their frequency of occurrence was higher in control than in treatment samples. 5. Preliminary results with amplified and cloned 18S DNA sequences revealed many fungal taxa with high affinities to Basidiomycota, particularly to Limnoperdon incarnatum. 6. By itself, higher water temperature due to global warming is likely to lower the availability of substrates for, and therefore the occurrence of, aquatic hyphomycetes.

Summary Climate change scenarios predict an increase in global temperature and alterations in precipitation regimes, which may change nutrient concentrations in waterbodies. In forested streams, decomposition of allochthonous organic matter is a key ecosystem process that is affected by the quality of plant litter entering the streams and several environmental factors, including nutrient concentrations, whose interactive effects are difficult to predict. We examined the concomitant effects of increased temperature, concentration of inorganic nutrients in stream water and litter quality on leaf decomposition and activity of microbial decomposers. Leaves of alder (Alnus glutinosa) and oak (Quercus robur), representative of high and low initial N content, respectively, were immersed in a stream (NW Portugal) to allow microbial colonisation and then were exposed in microcosms to increasing concentrations of N‐NO3 (0.09–5 mg L−1; six levels) and P‐PO4 (0.003–0.3 mg L−1; three levels) alone or in all possible combinations. One set of microcosms was kept at 12 °C, a temperature typically found in Iberian streams in autumn, and the other set at 18 °C to simulate a warming scenario. Nitrogen immobilisation was higher in alder than in oak leaves, and increased with temperature and N concentration in stream water for both leaf species. Leaf decomposition, fungal biomass accrual and reproduction were not affected by P concentration, but overall microbial activity increased asymptotically (Michaelis–Menten kinetics) with N concentration. Increased temperature led to an increase in maximum activity of fungal decomposers and to a decrease in N concentration needed to achieve it, especially in alder leaves. Under the predicted warming scenario, leaf decomposition may become faster in streams with lower nutrient levels, especially those receiving high‐quality leaf litter.

Leaf disks of Tilia cordata were exposed for up to 5 weeks in a first-order stream in Nova Scotia, Canada. The exponential decay rate k was 0.008 day(-1). Ergosterol levels increased linearly to a maximum of 134 microg g(-1) dry leaf mass. Release of conidia peaked at 700 day(-1) mg(-1) on leaves that had been exposed for 3 weeks; after 5 weeks, it declined to 15 mg(-1). In total, 23 taxa of aquatic hyphomycetes were distinguished. Anguillospora filiformis contributed over 76% of the conidia during weeks 1, 2, and 3, and 16.5% in week 5. Three sets of primers specific for Bacteria, Archaea, and Fungi were applied in quantitative real-time polymerase chain reaction (Q-RT-PCR) to estimate relative DNA amounts. Archaeal DNA was consistently present at low levels. Bacterial and fungal DNA peaked between weeks 2 and 3, and declined in week 5. With the exception of week 1, fungal DNA exceeded bacterial DNA by between 12 and 110%.

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.

Effects of gamma irradiation on Mucuna pruriens seeds at various doses (0, 2.5, 5, 7.5, 10, 15 and 30 kGy) on the proximate composition, mineral constituents, amino acids, fatty acids and functional properties were investigated. Gamma irradiation resulted in a significant increase of crude protein at all doses, while the crude lipid, crude fibre and ash showed a dose-dependent decrease. Raw Mucuna seeds were rich in minerals (potassium, phosphorus, calcium, magnesium, iron and selenium). Sodium, copper and manganese were significantly decreased on irradiation at all the doses, while magnesium and iron showed a significant decrease only above 10 kGy. The essential amino acids of raw and gamma-irradiated Mucuna seeds were comparable with the FAO/WHO recommended pattern. A significant increase of in vitro protein digestibility was seen in seeds irradiated at 30 kGy. High amounts of unsaturated fatty acids in Mucuna seeds decreased significantly after irradiation. However, linoleic acid was not present in raw seeds but detected after irradiation and it was elevated to high level at 30 kGy. Behenic acid, a major anti-nutritional factor, was reduced significantly on irradiation, indicating the positive effect of gamma irradiation on Mucuna seeds. Significant enhancement in the water absorption and oil absorption capacities, protein solubility, emulsion activity and improvement in the gelation capacity was recorded after irradiation. Results of the present investigation reveal that application of gamma irradiation does not affect the overall nutritional composition and can be used as an effective method of preservation of Mucuna seed and their products.