Aquatic Fungi Research Articles

The aquatic hyphomycete Heliscus lugdunensis protects its hyphae tip cells from cadmium: A micro X-ray fluorescence and X-ray absorption near edge structure spectroscopy study

Aquatic fungi can be used to evaluate the functioning of natural ecosystems. Heliscus lugdunensis is an early colonizer of allochthone leafs. Since this aquatic hyphomycete is able to develop in metal contaminated habitats and tolerates cadmium, it appears to be a good candidate to investigate adaptation to metal pollution. This study aimed at examining the sequestration of Cd in the hyphae of H. lugdunensis, and particularly the role of the tip cells. For that, H. lugdunensis growth was evaluated under various Cd concentrations, and a combination of synchrotron micro X-ray fluorescence and X-ray absorption near edge structure spectroscopy was carried out to determine the compartments of Cd accumulation and the Cd chemical species, respectively. Results showed that the hyphal tip cells were depleted in Cd, and that the metal was stored in older cells. Cd was mainly associated with sulfur ligands and to a lesser extent bound to phosphates and carboxyl/hydroxyl groups from cell wall and/or organic acids. Finally, the aquatic fungus was able to maintain the tip cell as a functional system, thus allowing the colonization of contaminated environments.

Organic matter quality structures benthic fatty acid patterns and the abundance of fungi and bacteria in temperate lakes

Benthic microbial communities (BMCs) play important roles in the carbon cycle of lakes, and benthic littoral zones in particular have been previously highlighted as biogeochemical hotspots. Dissolved organic matter (DOM) presents the major carbon pool in lakes, and although the effect of DOM composition on the pelagic microbial community composition is widely accepted, little is known about its effect on BMCs, particularly aquatic fungi. Therefore, we investigated the composition of benthic littoral microbial communities in twenty highly diverse lakes in northeast Germany. DOM quality was analyzed via size exclusion chromatography (SEC), fluorescence parallel factor analyses (PRAFACs) and UV–Vis spectroscopy. We determined the BMC composition and biomass using phospholipid-derived fatty acids (PLFA) and extended the interpretation to the analysis of fungi by applying a Bayesian mixed model. We present evidence that the quality of DOM structures the BMCs, which are dominated by heterotrophic bacteria and show low fungal biomass. The fungal biomass increases when the DOM pool is processed by microorganisms of allochthonous origin, whereas the opposite is true for bacteria.

Taxonomy, phylogeny and ecology of cultivable fungi present in seawater gradients across the Northern Antarctica Peninsula.

Thirty-six seawater samples collected at different depths of the Gerlache and Bransfield Straits in the Northern Antarctic Peninsula were analyzed, and the average of the total fungal counts ranged from 0.3 to >300 colony forming units per liter (CFU/L) in density. The fungal were purified and identified as 15 taxa belonged to the genera Acremonium, Aspergillus, Cladosporium, Cystobasidium, Exophiala, Glaciozyma, Graphium, Lecanicillium, Metschnikowia, Penicillium,Purpureocillium and Simplicillium. Penicillium chrysogenum, Cladosporium sphaerospermum, and Graphium rubrum were found at high densities in at least two different sites and depths. Our results show at the first time that in the seawater of Antarctic Ocean occur diverse fungal assemblages despite extreme conditions, which suggests the presence of a complex aquatic fungi food web, including species reported as barophiles, symbionts, weak and strong saprobes, parasites and pathogens, as well as those found in the polluted environments of the world. Additionally, some taxa were found in different sites, suggesting that the underwater current might contribute to fungal (and microbial) dispersal across the Antarctic Ocean, and nearby areas such as South America and Australia.

Allelopathic inhibition of primary producer growth and photosynthesis by aquatic fungi

Autochthonous primary production is generally much reduced in forested headwater streams. Several hypotheses have been proposed for explaining this observation, among them, the low light intensity, or the strong constraints exerted by stream current. Allelopathic inhibition of competitors is a common ecological process in aquatic environments. Aquatic hyphomycetes are known to chemically inhibit bacteria and other fungi (including other aquatic hyphomycetes) but a possible allelopathic effect of aquatic hyphomycetes on primary producers has never been tested. The inhibitory effect of twelve aquatic hyphomycete species was tested on three diatom species. Nine aquatic hyphomycete species exhibited anti-diatom activity. Up to 100% diatom growth inhibition was observed. Our study reveals that such allelopathic interactions might be common in streams and probably involve an array of fungal compounds. We propose that the generally reduced primary production observed in forested headwater streams is, among other factors, due to the inhibition of primary producers by allelopathic compounds released by aquatic hyphomycetes.

Changes in nutrient stoichiometry, elemental homeostasis and growth rate of aquatic litter-associated fungi in response to inorganic nutrient supply.

Aquatic fungi mediate important energy and nutrient transfers in freshwater ecosystems, a role potentially altered by widespread eutrophication. We studied the effects of dissolved nitrogen (N) and phosphorus (P) concentrations and ratios on fungal stoichiometry, elemental homeostasis, nutrient uptake and growth rate in two experiments that used (1) liquid media and a relatively recalcitrant carbon (C) source and (2) fungi grown on leaf litter in microcosms. Two monospecific fungal cultures and a multi-species assemblage were assessed in each experiment. Combining a radioactive tracer to estimate fungal production (C accrual) with N and P uptake measurements provided an ecologically relevant estimate of mean fungal C:N:P of 107:9:1 in litter-associated fungi, similar to the 92:9:1 obtained from liquid cultures. Aquatic fungi were found to be relatively homeostatic with respect to their C:N ratio (~11:1), but non-homeostatic with respect to C:P and N:P. Dissolved N greatly affected fungal growth rate and production, with little effect on C:nutrient stoichiometry. Conversely, dissolved P did not affect fungal growth and production but controlled biomass C:P and N:P, probably via luxury P uptake and storage. The ability of fungi to immobilize and store excess P may alter nutrient flow through aquatic food webs and affect ecosystem functioning.

Taxa-area relationship of aquatic fungi on deciduous leaves.

One of the fundamental patterns in macroecology is the increase in the number of observed taxa with size of sampled area. For microbes, the shape of this relationship remains less clear. The current study assessed the diversity of aquatic fungi, by the traditional approach based on conidial morphology (captures reproducing aquatic hyphomycetes) and next generation sequencing (NGS; captures other fungi as well), on graded sizes of alder leaves (0.6 to 13.6 cm2). Leaves were submerged in two streams in geographically distant locations: the Oliveira Stream in Portugal and the Boss Brook in Canada. Decay rates of alder leaves and fungal sporulation rates did not differ between streams. Fungal biomass was higher in Boss Brook than in Oliveira Stream, and in both streams almost 100% of the reads belonged to active fungal taxa. In general, larger leaf areas tended to harbour more fungi, but these findings were not consistent between techniques. Morphospecies-based diversity increased with leaf area in Boss Brook, but not in Oliveira Stream; metabarcoding data showed an opposite trend. The higher resolution of metabarcoding resulted in steeper taxa-accumulation curves than morphospecies-based assessments (fungal conidia morphology). Fungal communities assessed by metabarcoding were spatially structured by leaf area in both streams. Metabarcoding promises greater resolution to assess biodiversity patterns in aquatic fungi and may be more accurate for assessing taxa-area relationships and local to global diversity ratios.

Structural and functional responses of leaf‐associated fungal communities to chemical pollution in streams

Abstract The decomposition of allochthonous plant litter is a key ecological process in forested streams, involving the lignolytic activities of aquatic fungi. In this study we investigated the relationship between water pollution (by a mixture of nutrients, metals and pesticides) and the biomass, structure and enzyme activities of leaf‐associated fungal communities. The experiment was performed through a microcosm approach by comparing fungal communities from a less‐polluted upstream site to a more‐polluted downstream site in the agricultural basin of the Auzon stream (Puy‐de‐Dôme region, Centre France). The resistance as well as the ability of these fungal communities to recover from pollution was also assessed through a translocation experiment. Results showed a lower laccase activity and higher band richness in fungal communities from the downstream site comparing to the upstream site, which can partially be explained by the greater pesticide toxicity and concentration of dissolved organic carbon of downstream waters. Specifically, a negative relationship between laccase activity and nitrate concentration was observed, irrespectively of the studied site, whereas the relationship between nitrate and phenol oxidase/peroxidase appeared much weaker. The translocation experiment evidenced (1) a fast decrease in laccase activity concomitant with a shift in fungal structure after stress exposure, and (2) a recovery ability in terms of laccase activity and fungal community structure 2 weeks after stress removal. This study underlines the sensitivity of leaf‐associated fungal communities in terms of laccase activity and community structure to variations in chemical stress, as well as their ability to recover once the stress is removed. This study highlights the potential use of laccase as an indicator of chemical pollution of streams.

The Occurrence and Diversity of Waterborne Fungi in African Aquatic Systems: Their Impact on Water Quality and Human Health.

Currently, there is a worldwide growing interest in the occurrence and diversity of fungi and their secondary metabolites in aquatic systems, especially concerning their role in water quality and human health. However, this concern is hampered by the scant information that is available in the literature about aquatic fungi and how they affect water quality. There are only few published reports that link certain species of aquatic fungi to human health. The common aquatic fungal species that have been reported so far in African aquatic systems belong to the hyphomycetes kingdom. This paper thus aims to survey the information about the occurrence and factors that control the distribution of different species of fungi in African aquatic systems, as well as their effect on water quality and the possible metabolic pathways that lead to the formation of toxic secondary metabolites that are responsible for the deterioration of water quality. This review will also investigate the analytical and bioanalytical procedures that have been reported for the identification of different species of waterborne fungi and their secondary metabolites.

Fungal communities in Scandinavian lakes along a longitudinal gradient

Abstract This study investigates the diversity and distribution of fungal communities in 77 oligotrophic lakes in southern Norway and Sweden using 454-sequencing with fungal-specific primers targeting ITS2 region of the rRNA gene. A total of 232 operational taxonomic units (OTUs) belonging to four recognized phyla were detected. A large proportion (70.69%) of the detected OTUs were Dikarya (Ascomycota and Basidiomycota), while Chytridiomycota dominated quantitatively (63.37% reads). The most abundant aquatic fungi were taxonomically assigned to Chytridiomycota, whose members are known to be saprobes on a large variety of substrates and parasites of phytoplankton, zooplankton, fungi and invertebrates, suggesting that resident fungi strictly depend on surfaces and, therefore, are closely associated with other types of aquatic organisms. Our results indicate that surface waters of oligotrophic lakes harbour a diverse pool of fungi, both with tentative terrestrial and true aquatic origin. Longitude and environmental factors were important in structuring the fungal community composition.

Chytrid fungus infection in zebrafish demonstrates that the pathogen can parasitize non-amphibian vertebrate hosts

Aquatic chytrid fungi threaten amphibian biodiversity worldwide owing to their ability to rapidly expand their geographical distributions and to infect a wide range of hosts. Combating this risk requires an understanding of chytrid host range to identify potential reservoirs of infection and to safeguard uninfected regions through enhanced biosecurity. Here we extend our knowledge on the host range of the chytrid Batrachochytrium dendrobatidis by demonstrating infection of a non-amphibian vertebrate host, the zebrafish. We observe dose-dependent mortality and show that chytrid can infect and proliferate on zebrafish tissue. We also show that infection phenotypes (fin erosion, cell apoptosis and muscle degeneration) are direct symptoms of infection. Successful infection is dependent on disrupting the zebrafish microbiome, highlighting that, as is widely found in amphibians, commensal bacteria confer protection against this pathogen. Collectively, our findings greatly expand the limited tool kit available to study pathogenesis and host response to chytrid infection.

Optical Control of cGMP Signaling

Zoospores of the aquatic fungi Blastocladiella emersonii are phototactic and a rhodopsin-guanylyl cyclase (RhGC) was identified as the putative phototaxis receptor. Due to the direct linkage between the rhodopsin and the cyclase domain, RhGC represents the first member of a novel class of enzyme linked rhodopsins. In this work, we characterized RhGC biophysically. We show that green light maximally activates RhGC and cyclic GMP is produced. After a short green laser flash, RhGC (D525) converts in 8 ms into a blue-shifted signaling state P380 and recovers within 100 ms. RhGC expresses well in Xenopus oocytes, yeast, CHO cells, mammalian neurons and cyclic GMP production was light dose-dependent, rapid and reproducible. Thus, RhGC is a versatile tool for optogenetic analysis of cGMP-dependent signaling processes in cell biology and the neurosciences.

Distinct sensitivity of fungal freshwater guilds to water quality

Multiple anthropogenic stressors have been shown to impact animal and plant communities in freshwater ecosystems, but the responses of aquatic fungi remain largely unknown. Stressor effects on fungal communities may, however, result in changes of decomposition of plant litter and, thus, impact nutrient cycling, a key process for ecosystem functioning. We tested the impact of increased chloride and sediment levels, as well as reduced water flow velocity, on eukaryotic freshwater communities, with an emphasis on fungi, in a mesocosm experiment. Each of the three stressors was applied individually and in all combinations in a full-factorial design. Litterbags with non-sterilised tree leaves and sterile ceramic tiles were added to the mesocosms, to analyse the responses of communities in decaying plant material and in biofilms. Fungi preferably occurring in biofilms were supposed to represent indigenous aquatic fungi, while litterbag communities should be predominantly composed of fungi known from terrestrial litter. Community composition was assessed by high-throughput sequencing of amplified barcoding regions. Similarity matrices of operational taxonomic unit (OTU) tables calculated by UCLUST and CD-HIT-OTU-Illumina were significantly correlated. Preferred occurrence in biofilm and litter communities, respectively, was used for the grouping of OTUs into three ecological guilds. Stressor sensitivity varied among the guilds. While non-fungal, in particular autotrophic, OTUs responded to several treatments, two of the fungal guilds, i.e. those exclusively colonising litter and those preferably occurring on the ceramic tiles, showed no response to any applied treatment. Only fungi preferably, but not exclusively, colonising litter significantly responded to chloride addition. Their distribution patterns again correlated significantly with those of non-fungal OTUs, indicating possible interdependencies between both groups. The results indicate that eukaryotic freshwater communities are composed of different guilds, with distinctive sensitivity and tolerance to anthropogenic stressors.

Fungal\u2013bacterial dynamics and their contribution to terrigenous carbon turnover in relation to organic matter quality

Ecological functions of fungal and bacterial decomposers vary with environmental conditions. However, the response of these decomposers to particulate organic matter (POM) quality, which varies widely in aquatic ecosystems, remains poorly understood. Here we investigated how POM pools of substrates of different qualities determine the relative contributions of aquatic fungi and bacteria to terrigenous carbon (C) turnover. To this end, surface sediments were incubated with different POM pools of algae and/or leaf litter. 13C stable-isotope measurements of C mineralization were combined with phospholipid analysis to link the metabolic activities and substrate preferences of fungal and bacterial heterotrophs to dynamics in their abundance. We found that the presence of labile POM greatly affected the dominance of bacteria over fungi within the degrader communities and stimulated the decomposition of beech litter primarily through an increase in metabolic activity. Our data indicated that fungi primarily contribute to terrigenous C turnover by providing litter C for the microbial loop, whereas bacteria determine whether the supplied C substrate is assimilated into biomass or recycled back into the atmosphere in relation to phosphate availability. Thus, this study provides a better understanding of the role of fungi and bacteria in terrestrial–aquatic C cycling in relation to environmental conditions.

Using aquatic fungi for pharmaceutical bioremediation: Uptake of acetaminophen by Mucor hiemalis does not result in an enzymatic oxidative stress response

The increasing anthropogenic pollution of aquatic environments and fresh water scarcity worldwide have prompted the development of low-cost and effective water treatment alternatives. One example of a highly released anthropogenic xenobiotics is acetaminophen (APAP), which has been detected in surface waters at concentrations as high as 5 μg L−1. To date, traditional water treatment plants were unable to remove all pharmaceutical xenobiotics and as in the case with APAP, the breakdown products are toxic. Phytoremediation has proved to remove xenobiotics efficiently producing no toxic breakdown products, however, they are often restrained in their application range. Therefore, it was necessary to find alternate remediation tools to extend and complement the application ranges of existing bioremediation techniques. With the success of mycoremediation as well as the adaptability of fungi, Mucor hiemalis was investigated in terms of its APAP uptake capabilities. The investigation included the examination of concentration- and time-dependent uptake studies to examine the effects of each of these parameters independently. Additionally, the extracellular peroxidase activity of M. hiemalis was measured with exposure to APAP to evaluate possible breakdown and the antioxidative stress enzymes, catalase, glutathione peroxidase, and glutathione reductase, were assayed to investigate whether APAP caused oxidative stress. The results showed that M. hiemalis was able to internalize between 1 and 2 μg APAP per g dried fungal biomass when exposed to 5, 10, 50 and 100 ng mL−1 APAP for 24–48 h, but not beyond this time frame. Further, exposure to APAP did not result in elevated extracellular peroxidase activity or oxidative stress. The findings led to the conclusion that M. hiemalis could be integrated in bioremediation systems, for short-term degradation at low concentrations of APAP with effective management.

Spatial distribution of aquatic marine fungi across the western Arctic and sub-arctic.

Fungi are important parasites of primary producers and nutrient cyclers in aquatic ecosystems. In the Pacific-Arctic domain, fungal parasitism is linked to light intensities and algal stress that can elevate disease incidence on algae and reduce diatom concentrations. Fungi are vastly understudied in the marine realm and knowledge of their function is constrained by the current understanding of fungal distribution and drivers on global scales. To investigate the spatial distribution of fungi in the western Arctic and sub-Arctic, we used high throughput methods to sequence 18S rRNA, cloned and sequenced 28S rRNA and microscopically counted chytrid-infected diatoms. We identified a broad distribution of fungal taxa predominated by Chytridiomycota and Dikarya. Phylogenetic analysis of our Chytridiomycota clones placed Arctic marine fungi sister to the order Lobulomycetales. This clade of fungi predominated in fungal communities under ice with low snowpack. Microscopic examination of fixed seawater and sea ice samples revealed chytrids parasitizing diatoms collected across the Arctic that notably infected 25% of a single diatom species in the Bering Sea. The Pezizomycotina comprised > 95% of eukaryotic sequence reads in Greenland, providing preliminary evidence for osmotrophs being a substitute for algae as the base of food webs.

Novel chytrid lineages dominate fungal sequences in diverse marine and freshwater habitats.

In aquatic environments, fungal communities remain little studied despite their taxonomic and functional diversity. To extend the ecological coverage of this group, we conducted an in-depth analysis of fungal sequences within our collection of 3.6 million V4 18S rRNA pyrosequences originating from 319 individual marine (including sea-ice) and freshwater samples from libraries generated within diverse projects studying Arctic and temperate biomes in the past decade. Among the ~1.7 million post-filtered reads of highest taxonomic and phylogenetic quality, 23,263 fungal sequences were identified. The overall mean proportion was 1.35%, but with large variability; for example, from 0.01 to 59% of total sequences for Arctic seawater samples. Almost all sample types were dominated by Chytridiomycota-like sequences, followed by moderate-to-minor contributions of Ascomycota, Cryptomycota and Basidiomycota. Species and/or strain richness was high, with many novel sequences and high niche separation. The affinity of the most common reads to phytoplankton parasites suggests that aquatic fungi deserve renewed attention for their role in algal succession and carbon cycling.

Effects of two fungicide formulations on microbial and macroinvertebrate leaf decomposition under laboratory conditions.

Aquatic fungi contribute significantly to the decomposition of leaves in streams, a key ecosystem service. Little is known, however, about the effects of fungicides on aquatic fungi and macroinvertebrates involved with leaf decomposition. Red maple (Acer rubrum) leaves were conditioned in a stream to acquire microbes (bacteria and fungi) or leached in tap water (unconditioned) to simulate potential reduction of microbial biomass by fungicides. Conditioned leaves were exposed to fungicide formulations QUILT (azoxystrobin + propiconazole) or PRISTINE (boscalid + pyraclostrobin) in the presence and absence of the leaf shredder, Hyalella azteca (amphipods; 7-d old at start of exposures) for 14 d at 23 °C. The QUILT formulations (∼0.3 μg/L, 1.8 μg/L, and 8 μg/L) tended to increase leaf decomposition by amphipods (not significant) without a concomitant increase in amphipod biomass, indicating potential increased consumption of leaves with reduced nutritional value. The PRISTINE formulation (∼33 μg/L) significantly reduced amphipod growth and biomass (p < 0.05), effects similar to those observed with unconditioned controls. The significant suppressive effects of PRISTINE on amphipod growth and the trend toward increased leaf decomposition with increasing QUILT concentration indicate the potential for altered leaf decay in streams exposed to fungicides. Further work is needed to evaluate fungicide effects on leaf decomposition under conditions relevant to stream ecosystems, including temperature shifts and pulsed exposures to pesticide mixtures. Environ Toxicol Chem 2016;35:2834-2844. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Таксономическое разнообразие микобиоты прибрежных вод Крыма (Чёрное море)

Новые сведения о распространении грибов, смена родовых названий и изменение систематического положения некоторых видов обуславливают необходимость ревизии микобиоты прибрежных вод Крыма. Цель работы ― на основе литературных и собственных данных провести ревизию синонимики названий грибов, выявить видовое богатство, дать количественную оценку и выполнить сравнительный анализ таксономического разнообразия микобиоты различных районов и биотопов черноморского сектора прибрежных вод Крыма и западной халистазы. Исследованы биотопы: вода, донные отложения, водоросли, покровы беспозвоночных животных, кожа дельфинов, Zostera marina и древесина. Список видов микроскопических грибов включал 275 видов из 105 родов, 40 семейств, 26 порядков, 15 классов, 5 отделов. Число видов по районам изменялось от 19 (6,9 % от видового состава) в западной халистазе до 147 (53,4 %) в бухте Казачья, по биотопам ― от 17 (6,2 %) на коже дельфинов до 157 (57,1 %) в донных отложениях. Оценка видового разнообразия грибов выполнена с использованием индексов таксономической отличительности TaxDI (Δ+ и Λ+). Минимальная таксономическая сложность разнообразия (Δ+ = 66,4) определена в районе западной халистазы, максимальная в б. Севастопольская (Δ+ = 80,2). На древесине выявлено минимальное значение индекса (Δ+ = 70,0), на беспозвоночных ― максимальное (Δ+ = 86,2). Наименьшей таксономической сложностью характеризовались комплексы, в которых основа видового состава (81,8–89,5 % по районам и 76,5–87,1 % по биотопам) была представлена поливидовыми ветвями микобиоты из «ведущих» семейств и родов. Число исследованных биотопов определило отличительные особенности иерархического разнообразия микобиоты. На структуру комплексов грибов влияли облигатно морские виды, выделенные с беспозвоночных животных и фрагментов древесины. Максимальное сходство микокомплексов на всех таксономических уровнях отмечено в бухтах Казачья и Камышовая, минимальное ― для микокомплексов западной халистазы и б. Севастопольская, наибольшее сходство структуры зафиксировано в биотопах воды и донных отложений, наименьшее ― в биотопах воды и древесины.

Stoichiometric constraints modulate impacts of silver contamination on stream detritivores: an experimental test with Gammarus fossarum

Summary Organisms commonly face multiple stresses in ecosystems, among which are toxic substances that add to natural ecological constraints such as insufficient resource quality. The combined effects of these stressors on species and ecosystems remain poorly investigated. We hypothesised that feeding on high‐quality resources in terms of phosphorus (P) content will improve the physiological state of consumers and thus increase tolerance to episodic metal stress by silver (Ag). We used a detritivorous crustacean from streams, Gammarus fossarum, to test this hypothesis. The experimental design involved two phases. In the first phase, gammarids were fed ad libitum for 15 days to evaluate the effect of food quality on their energetic status. Gammarids were placed in laboratory microcosms and allowed to feed on two leaf species, alder and sycamore, that were colonised by aquatic fungi and experimentally enriched with P. At the end of this feeding period, we determined (i) food consumption, (ii) energetic reserves and (iii) physiological and behavioural states. In the second phase, gammarids previously consuming food of different quality were exposed to dissolved Ag (0, 0.5 and 1 μg L−1) for 4 days to investigate the physiological and behavioural responses of the consumers. Elevated P concentrations in leaf litter increased the energetic reserves and locomotor activity of G. fossarum. Gammarids exposed to Ag had a low glycogen content, regardless of the Ag concentration and leaf P concentration, suggesting significant energy allocation to several aspects of organism maintenance (e.g. detoxification or compensatory mechanisms). In most cases, this investment appeared to prevent gammarids from carrying out lipid peroxidation (indicating cell membrane damage), except for those gammarids feeding on leaves with the highest P concentration. Higher energetic storage (measured as glycogen content), related to higher elemental food quality, did not lead to a systematic increase in consumer tolerance to Ag, gammarids being unable to compensate for negative effects of Ag at the concentrations tested.

Shifts in leaf litter breakdown along a forest-pasture-urban gradient in Andean streams.

Tropical montane ecosystems of the Andes are critically threatened by a rapid land‐use change which can potentially affect stream variables, aquatic communities, and ecosystem processes such as leaf litter breakdown. However, these effects have not been sufficiently investigated in the Andean region and at high altitude locations in general. Here, we studied the influence of land use (forest–pasture–urban) on stream physico‐chemical variables (e.g., water temperature, nutrient concentration, and pH), aquatic communities (macroinvertebrates and aquatic fungi) and leaf litter breakdown rates in Andean streams (southern Ecuador), and how variation in those stream physico‐chemical variables affect macroinvertebrates and fungi related to leaf litter breakdown. We found that pH, water temperature, and nutrient concentration increased along the land‐use gradient. Macroinvertebrate communities were significantly different between land uses. Shredder richness and abundance were lower in pasture than forest sites and totally absent in urban sites, and fungal richness and biomass were higher in forest sites than in pasture and urban sites. Leaf litter breakdown rates became slower as riparian land use changed from natural to anthropogenically disturbed conditions and were largely determined by pH, water temperature, phosphate concentration, fungal activity, and single species of leaf‐shredding invertebrates. Our findings provide evidence that leaf litter breakdown in Andean streams is sensitive to riparian land‐use change, with urban streams being the most affected. In addition, this study highlights the role of fungal biomass and shredder species (Phylloicus; Trichoptera and Anchytarsus; Coleoptera) on leaf litter breakdown in Andean streams and the contribution of aquatic fungi in supporting this ecosystem process when shredders are absent or present low abundance in streams affected by urbanization. Finally, we summarize important implications in terms of managing of native vegetation and riparian buffers to promote ecological integrity and functioning of tropical Andean stream ecosystems.