Ana Lúcia Gonçalves

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.

Effects of Eucalyptus leachates and oxygen on leaf-litter processing by fungi and stream invertebrates

Abstract.  In summer, streams in Portuguese eucalyptus forests frequently experience drought resulting in isolated pools, frequently saturated with leaf litter, in which the leaf leachates may generate toxic and hypoxic conditions. We assessed the ecological effects of Eucalyptus globulus leachate with and without aeration (i.e., low flow vs pool scenarios) on microbial decomposition of eucalyptus leaves and on toxicity to and survival, avoidance, and feeding behavior of Chironomus riparius Meigen (Diptera:Chironomidae), Echinogammarus meridionalis Pinkster (Amphipoda:Gammaridae), and Sericostoma vittatum Rambur (Trichoptera:Sericostomatidae). Eucalyptus globulus leaves immersed in a gradient of aerated or nonaerated eucalyptus leachate (100, 40.0, 16.0, 6.40, 2.50% volume/volume) were colonized by species-poor fungal assemblages. Leaf mass loss did not differ among treatments, but hypoxia suppressed conidia production and negatively affected fungal biomass. A concentration-dependent effect on fungal biomass was observed in aerated leaf extracts. A trade-off was found between the stimulatory effect of leachate nutrients and inhibitory effects of secondary compounds at leachate concentrations of 16 to 40%, and microbial respiration was depressed at concentrations >16% in nonaerated conditions. Only S. vittatum discriminated leaves conditioned in aerated water from leaves conditioned in nonaerated leachates. Leachates negatively affected all species, mostly in nonaerated conditions. Maximum leachate concentration caused mortality of 100% of E. meridionalis and 26 to 40% of C. riparius, regardless of aeration, and 70% of S. vittatum in nonaerated conditions. Sericostoma vittatum avoided the highest leachate concentrations, but C. riparius and E. meridionalis did not. Impoverished microbial communities and invertebrate assemblages with dissimilar tolerance to leachate may maintain functional properties and processes during drought disturbances in eucalyptus streams.

Decomposition of eucalypt and alder mixtures: responses to variation in evenness.

The relationship between diversity and function has only recently been investigated in stream ecosystems. Here we evaluated the effect of litter evenness on litter decomposition in single species and 2-species litter bags with Alnus glutinosa (L.) Gaertn. (A) and Eucalyptus globulus Labill. (E).The five evenness treatments (100%A, 25%E + 75%A, 50%A + 50%E, 75%E + 25%A and 100%E) simulated the relative proportions of both leaf species throughout the year in a eucalypt stream lined by alder trees. Decomposition rates of eucalypt were retarded in the presence of alder, while those of alder were stimulated in the presence of eucalypt. Differences in mass loss between treatments were unrelated to the initial quality of the mixtures. Globally, the effects of litter evenness on microbial parameters (O 2 consumption, fungal biomass and sporulation) and invertebrate numbers ranged from undetectable to weak. This was probably due to high nutrient concentrations in the stream water that may have masked the potential stimulating effects promoted by the high quality of alder leaves on eucalypt biotic degradation. Although the effects of litter evenness on biotic parameters were idiosyncratic, the importance of species evenness on litter mass loss was suggested by the higher decomposition rates of the 50%:50% mixture, which is likely related to a trade-off between alder high nutrient quality and the stability promoted by eucalypt in the mixture. Alterations in litter evenness, resulting from changes in riparian composition and diversity, might affect litter decomposition, and consequently ecosystem function. These findings could be relevant for recovery and management of riparian zones.

Aquatic hyphomycete strains from metal-contaminated and reference streams might respond differently to future increase in temperature.

Aquatic hyphomycetes, a group of polyphyletic fungi, have been reported in streams contaminated with metals. This tolerance to metal contamination however can result in limited performance and limited ability to cope with additional environmental change. The predicted increase in water temperature, as a consequence of global warming, will have an additional effect on many streams. The sensitivity to temperature of strains of three aquatic hyphomycete species isolated from a metal-contaminated stream and an uncontaminated stream was assessed by determining their radial growth and activity (conidial production, oxygen consumption, mycelial biomass accumulation, fine particulate organic matter [FPOM] production, and microbial induced leaf mass loss) at 13 C (present water temperature in autumn) and at 18 C (predicted water temperature under global warming). Growth and reproductive activity generally were depressed for the strains isolated from the metal-contaminated stream when compared with those isolated from the unpolluted stream. These differences however were not translated into differences in FPOM production and leaf-litter mass loss, indicating that the strains isolated from the contaminated stream can decompose leaf litter similar to those of the reference stream. The 5 C increase in temperature stimulated fungal activity and litter decomposition, irrespective of species and strain. This might have strong effect on aquatic food-web and ecosystem functioning under global warming because increases in litter decomposition might lead to food shortage for higher trophic levels. The sensitivity to temperature depended on the response variable, species and strain. FPOM production was the variable most sensitive to temperature across strains and species and that for which temperature sensitivities differed most between strains. Fungal tolerance to metal contamination affects the extent to which its functions are stimulated by an increase in temperature, constituting an additional cost of metal tolerance.

The breakdown of Blue Gum (Eucalyptus globulus Labill.) bark in a Portuguese stream

Eucalypt forests produce large amounts of bark, which potentially accumulate in streams, constituting an important carbon and nutrient source for benthic food webs. In this study, we compared the breakdown (and associated microbial activity and diversity and invertebrate abundance) of Eucalyptus globulus bark and leaves, enclosed in coarse and fine mesh bags, in a 3 rd order stream of central Portugal. Biofilm development on bark was also analyzed with scanning electronic microscopy and respiration rates quantified. After 90 days of incubation, bark lost 21-51 % of its initial mass while leaves lost 48-57 %. Fungal biomass (as determined from ergosterol concentrations) increased over time and was higher in leaves than in bark (79 vs. 50 mg [g AFDM] -1 at day 90). Sporulation by aquatic hyphomycetes was only observed after 2 weeks (leaves and bark in coarse mesh bags) or 2 months (bark in fine mesh bags). The initial litter mass converted into conidia in leaves was 7-45 fold the values found in bark. Fungal communities were dissimilar in the two substrates with bark presenting the lowest number of species. Lunulospora curvula and Anguillospora crassa dominated the fungal communities in bark, while L. curvula and Tetrachaetum elegans were the dominant species in leaves. Respiration rates, as a measurement of microbial activity, were lower in bark than in leaves (0.10 vs. 0.25 mg O 2 [g AFDM] -1 h -1 in fine mesh and 0.11 vs. 0.39 mg O 2 [g -1 AFDM] -1 h -1 in coarse mesh). Biofilms in bark clearly increased after 15 days of immersion and contributed to 6-85 % of total oxygen consumption. Overall, the results suggest that microbial decomposition pathways dominate the processing of eucalyptus leaves and bark, although leaching and physical fragmentation may stimulate and facilitate the breakdown of bark.

Stream salinization and fungal-mediated leaf decomposition: A microcosm study

Salinization is of major global concern due to its effect on stream biota, and ecosystem functions and services. In small streams, litter decomposition is a key ecosystem-level process driven by decomposers, mainly fungi (aquatic hyphomycetes), which link litter and invertebrates. Here we assessed the effects of an environmentally relevant range of salt additions (0, 2, 4, 8, 16gL-1 NaCl) on (1) fungal growth and species-specific reproductive output and (2) fungal mediated-decomposition of Quercus robur leaves. Growth rates of eight out of nine species of aquatic hyphomycetes were negatively affected by salinity at concentrations ≥4gL-1. EC50s were species-specific and ≥7.80gL-1. Distinct thresholds were observed for reproduction: only five species sporulated at 2gL-1, and a single one (Flagellospora curta) sporulated at 4 and 8gL-1 NaCl. Based on these results, we evaluated if tolerant fungal assemblages, with increasingly fewer species (9, 5, 1), were able to maintain similar functional functions and processes at the different salt levels. No significant differences were found in oak mass loss or sporulation rates at 0 or 2gL-1 NaCl; a clear inhibition of both parameters was observed at the highest concentrations (i.e., 4 and 8gL-1 NaCl). Different dominance patterns in multi-species fungal assemblages may determine bottom-up impacts on the stream food webs through effects on detritivore feeding preferences. Specific growth rate, characterized by RNA concentration, was higher in the single species, at the highest salt-concentration, and lower in the 9-species assemblage. Respiration was almost 2-times higher in mixed assemblages without added salt. Under salt-contamination, trade-offs between growth and sporulation seem to guarantee high levels of fungal growth and decomposition, particularly in multi-species assemblages. In the presence of salt contamination, aquatic hyphomycetes, even at reduced diversity, remain important drivers of leaf decomposition and ensure organic matter recycling.

Uranium adsorption by Articulospora tetracladia: can aquatic hyphomycetes be natural bioremediators of uranium contaminated streams?

Uranium concentration in the streams around abandoned uranium mines in central Portugal can be as high as 1.8 mg/L. Herein we assessed the kinetics of uranium adsorption by Articulospora tetracladia mycelium at 200 and 2000 μgU/L over 6h. Uranium adsoption was relatively fast with 18–50% uranium remaining in solution after 15 minutes and maximum adsorption of ~140 mgU/gDM at 2000 μgU/L after 6h. The fitting of the uranium uptake data to the Freundlich isotherm indicates monolayer uranium adsorption at the surface of the mycelium. The stability of the uranium monolayer is high (n 48203 mL/g) found for A. tetracladia indicate that this species can be considered a good biosorbent and has the ability to retrieve uranium from very dilute solutions (stream water). Aquatic hyphomycetes seem to have the potential to act as natural bioremediators of streams running through uranium contaminated areas.