Increase In Fungal Biomass Research Articles

Soil microbial community responses to long-term experimental warming in an alpine Dryas octopetala heath in Norway

Over the last century, high-altitude and high-latitude regions have experienced global warming at rates higher than the worldwide average. Climate change influences complex soil-microbe-plant-atmosphere interactions, leading to changes in plant-associated soil microbial diversity and functioning and alterations in nutrient cycling, carbon fluxes, and storage. This study analyzed how two decades of global warming simulated by open-top chambers (OTCs) affected soil bacterial and fungal communities in an alpine dwarf-shrub heath dominated by Dryas octopetala in Norway. We collected soil samples from 10 OTCs and 10 control plots and compared their physicochemical properties, microbial biomass, extracellular enzyme activities, and bacterial and fungal community diversity and composition. Warming did not significantly affect the bacterial community despite the tendency to reduce alpha diversity and increase the degree of specialisation. In contrast, two decades of warming significantly affected fungal community composition, which was dominated by ectomycorrhizal Basidiomycota. While there was no significant effect on the total fungal community diversity, a significant shift in saprotrophic Ascomycota taxa was observed between the warmed and control plots. Their positive correlations with oxidative enzymes and fungal biomass suggest that long-term warming might lead to an increase in fungal biomass and the activity of oxidative enzymes, promoting the decomposition of more recalcitrant biopolymers. This may result in an increase in CO2 flux into the atmosphere and a decrease in ecosystem C storage.

Diel variations of airborne microbes and antibiotic resistance genes in Response to urban PM2.5 chemical properties during the heating season

Among the components of fine particulate matter (PM2.5), the contributions of airborne microorganisms and antibiotic resistance genes (ARGs) to health risks have been overlooked. Airborne microbial dynamics exhibit a unique diurnal cycle due to environmental influences. However, the specific roles of PM2.5 chemical properties resulting from fossil fuel combustion in driving circadian fluctuations in microbial populations and ARGs remain unclear. This study explored the interactions between toxic components and microbial communities during the heating period to understand the variations in ARGs. Bacterial and fungal communities showed a higher susceptibility to diel variations in PM2.5 compared to their chemical properties. Mantel tests revealed that chemical properties and microbial community interactions contribute differently to ARG variations, both directly and indirectly, during circadian fluctuations. Our findings highlight that, during the daytime, the enrichment of pathogenic microorganisms and ARGs increases the risk of PM2.5 toxicity. Conversely, during the nighttime, the utilization of water-soluble ions by the fungal community increased, leading to a significant increase in fungal biomass. Notably, Aspergillus exhibited a significant correlation with mobile genetic elements and ARGs, implying that this genus is a crucial driver of airborne ARGs. This study provides novel insights into the interplay between the chemical composition, microbial communities, and ARGs in PM, underscoring the urgent need for a comprehensive understanding of effective air pollution control strategies.

Contrasting organic matter composition in pristine and eutrophicated mangroves revealed by fatty acids and stable isotopes (Rio de Janeiro, Brazil)

Mangrove sediments have a high capacity of carbon storage, as the result of larger organic matter (OM) inputs from mangrove trees (litter fall and fine roots production) than OM microbial degradation and export to coastal waters. Mangrove sediments also act as traps for suspended matter and particulate OM (POM) from surrounding water masses. Fatty acids (FAs) markers, δ13C and δ15N signatures were used here to characterize the OM composition in three mangroves located in three coastal embayments of the Rio de Janeiro state (Brazil) with increasing urbanization from a pristine mangrove M1 to a moderately impacted mangrove M2 and a highly impacted mangrove M3. In these mangroves, the δ15N signature of tree leaves and sediments increases with anthropogenic influence, consistent with a large-scale eutrophication gradient along the three regions. At mangrove M1, predominant OM inputs from mangrove trees are highlighted by high proportions of long-chain fatty acids, particularly in the inland station, where high organic carbon concentrations (126 ± 108 mg g−1) indicate limited sedimentation of mineral particles and high carbon storage capacities. The sedimentary OM of M3 mangrove was more labile as confirmed by the higher proportions of algal fatty acids, enriched δ13C signature and the C/N ratio 1.6 times lower (p < 0.001) than in the pristine mangrove M1. At the M2 mangrove site, high contribution of bacterial FAs (around 20%) to sedimentary OM and high proportion of poorly biodegradable saturated fatty acids suggest that bacteria degrade algal labile OM in surface sediments but do not mineralize the most refractory fraction of OM. At the eutrophic M3 site, our findings suggest that deposition of labile POM induced an increase of fungal biomass on the sediment, apparently enhancing the microbial loop, and potentially leading to mineralization of refractory OM and carbon losses through a priming effect.

Effects of Continuous Cropping of Dictyophora on Soil Physical and Chemical Properties, Microbial Biomass and Enzyme Activity

The continuous obstacle of Dictyophora indusiata has become the one of the main factors affecting the healthy development of D. indusiata industry. In order to study the effects of continuous cropping of D. indusiata on the soil environment, four treatments were used in this study: no planted (CK), planted for 1 years (1Y), continuous cropping for 2 years (2Y) and continuous cropping for 3 years (3Y), to determined of the yield of D. indusiata, soil physical and chemical properties, microbial content and enzyme activity. The results showed that the yield and soil pH value decreased with the increase of continuous cropping years, and the contents of organic matter, total nitrogen, total phosphorus and total potassium, C/N and C/P also increased with the increase of continuous cropping years. Soil availability decreased with the increase of continuous cropping years, the content of alkaline nitrogen, available phosphorus and available potassium decreased by 12.25%, 28.91% and 24.86% at 3Y compared with 1Y, respectively. The biomass of bacteria, actinomycetes and fungi and the total amount of microorganism in soil increased at 1Y compared with CK, but with the increase of continuous cropping years, the biomass of bacteria and actinomycetes and the total amount of microorganism decreased significantly, while the biomass of fungi increased significantly; the continuous cropping of D. indusiata also decreased the value of bacteria/fungi in soil. The enzyme activities of the soil were higher than those of the unplanted plots, however, the activities of urease, catalase, peroxidase, sucrase, phosphatase and protease decreased with the increase of continuous cropping years. In a word, with the increase of continuous cropping, the acidity of rhizosphere soil increased, the availability of soil nutrients and the activity of soil enzymes decreased, the biomass of soil microorganisms, bacteria and actinomycetes decreased. However, the increase of fungal biomass led to the decline of soil texture.

Graphene environmental biodegradation: Wood degrading and saprotrophic fungi oxidize few-layer graphene

The environmental biodegradability profile of graphene related materials (GRMs) is important to know in order to predict whether these materials will accumulate in soil or will be transformed by primary decomposers. In this study, few-layer graphene (FLG) was exposed to living and devitalized axenic cultures of two white-rot basidiomycetes (Bjerkandera adusta and Phanerochaete chrysosporium) and one soil saprotrophic ascomycete (Morchella esculenta) with or without lignin, for a period of four months. Over this time, the increase of fungal biomass and presence of H2O2 and oxidizing enzymes [laccase/peroxidase and lignin peroxidase (LiP)] in growth media was assessed by gravimetric and spectrophotometric measurements, respectively. Raman spectroscopy and transmission electron microscopy (TEM) were used to compare the structure of FLG before and after incubation. All of the test fungi decreased pH in growth media and released H2O2 and laccase/peroxidase, but only basidiomycetes released LiP. Independent of growth media composition all fungi were found to be capable to oxidize FLG to a graphene oxide-like material, including M. esculenta, which released only laccase/peroxidase, i.e. the most common enzymes among primary decomposers. These findings suggest that FLG involuntarily released into terrestrial environments would likely be oxidized by soil microflora.

Characterization of the Habitat- and Season-Independent Increase in Fungal Biomass Induced by the Invasive Giant Goldenrod and Its Impact on the Fungivorous Nematode Community

Outside its native range, the invasive plant species giant goldenrod (Solidago gigantea) has been shown to increase belowground fungal biomass. This non-obvious effect is poorly characterized; we don’t know whether it is plant developmental stage-dependent, which fractions of the fungal community are affected, and whether it is reflected in the next trophic level. To address these questions, fungal assemblages in soil samples collected from invaded and uninvaded plots in two soil types were compared. Although using ergosterol as a marker for fungal biomass demonstrated a significant increase in fungal biomass, specific quantitative PCR (qPCR) assays did not point at a quantitative shift. MiSeq-based characterization of the belowground effects of giant goldenrod revealed a local increase of mainly Cladosporiaceae and Glomeraceae. This asymmetric boost in the fungal community was reflected in a specific shift in the fungivorous nematode community. Our findings provide insight into the potential impact of invasive plants on local fungal communities.

Functional importance and diversity of fungi during standing grass litter decomposition.

Although microbial participation in litter decomposition is widely known within terrestrial soils, the role and significance of microorganisms during the aerial standing litter phase of decomposition remains poorly investigated. We examined the fungi inhabiting standing leaf litter of Schizachyrium scoparium and Schizachyrium tenerum in a Longleaf Pine savanna ecosystem and estimated their contribution to litter decomposition. We identified fungal phylotypes associated with leaf litter and quantified leaf C mass loss, fungal biomass production, and microbial respiration during decomposition. These data were used to construct budgets estimating C flow into and through fungi. Significant losses in S. scoparium (55%) and S. tenerum (67%) leaf C mass were observed during standing decomposition along with concomitant increases in fungal biomass, which reached a maximum of 36 and 33 mgC/g detrital C, respectively. Cumulative fungal production during decomposition totaled 99 ± 6 mgC/g initial detrital C in S. scoparium and 73 ± 5 mgC/g initial detrital C in S. tenerum, indicating that 18 and 11% of the litter C was converted into fungal biomass, respectively. Corresponding estimates of cumulative fungal respiration totaled 106 ± 7 and 174 ± 11 mgC/g initial detrital C in S. scoparium and S. tenerum, respectively. Next generation sequencing identified several fungal phylotypes, with the majority of sequences belonging to the Ascomycota (Dothideomycetes) and Basidiomycota (Agaricomycetes). Fungal phylotypes were similar between litter species and changed over time, showing a successional pattern. These findings extend our understanding of fungal processes to standing litter in terrestrial ecosystems, and highlight the quantitative importance of fungi in C cycling processes.

Application of monoclonal antibodies in quantifying fungal growth dynamics during aerobic spoilage of silage.

SummaryProliferation of filamentous fungi following ingress of oxygen to silage is an important cause of dry matter losses, resulting in significant waste. In addition, the production of mycotoxins by some filamentous fungi poses a risk to animal health through mycotoxicosis. Quantitative assessment of fungal growth in silage, through measurement of ergosterol content, colony‐forming units or temperature increase is limiting in representing fungal growth dynamics during aerobic spoilage due to being deficient in either representing fungal biomass or being able to identify specific genera. Here, we conducted a controlled environment aerobic exposure experiment to test the efficacy of a monoclonal antibody‐based enzyme‐linked immunosorbent assay (ELISA) to detect the proliferation of fungal biomass in six silage samples. We compared this to temperature which has been traditionally deployed in such experiments and on‐farm to detect aerobic deterioration. In addition, we quantified ergosterol, a second marker of fungal biomass. After 8 days post‐aerobic exposure, the ergosterol and ELISA methods indicated an increase in fungal biomass in one of the samples with a temperature increase observed after 16 days. A comparison of the methods with Pearson's correlation coefficient showed a positive association between temperature and ergosterol and both markers of fungal biomass. This work indicates that the technology has potential to be used as an indicator of microbial degradation in preserved forage. Consequently, if it developed as an on‐farm technique, this could inform forage management decisions made by farmers, with the goal of decreasing dry matter losses, improving resource and nutrient efficiency and reducing risks to animal health.

The hidden potential of saprotrophic fungi in arable soil: Patterns of short-term stimulation by organic amendments

Saprotrophic fungi are abundant in soils of (semi-)natural ecosystems, where they play a major role in ecosystem functioning. On the contrary, saprotrophic fungal biomass is remarkably low in intensively managed soils and this can have a negative impact on soil functioning. Nevertheless, arable soils harbour a diverse pool of fungi, which can be stimulated by organic amendments. Management targeted towards increasing soil organic matter often coincides with an increase of fungal biomass, but it can take years before effects are seen. However, a rapid stimulation of fungal biomass at the start of the growing season could immediately benefit crop production, by improving nutrient availability, soil structure and suppression of soil-borne diseases. The objective of this study is to realize a rapid increase of saprotrophic fungal biomass with organic amendments. In controlled pot experiments, dried and milled organic materials of different quality were added to an arable sandy soil. Ergosterol-based fungal biomass and ITS2-based fungal community structure were measured over a period of two months. Wood sawdust of deciduous tree species and paper pulp resulted in a high and lasting increase of fungal biomass, as opposed to transient effects given by cover crops and other non-woody plant materials. Little or no stimulation of fungi was seen for coniferous wood sawdust and agro-industrial by-products. Nitrogen immobilization induced by sawdust and paper pulp was compensated by supplementing mineral nitrogen, which enhanced the stimulation of saprotrophic fungi. The composition of the stimulated fungi was influenced by the quality of organic amendments. In particular, deciduous wood sawdust and paper pulp favoured saprotrophic ascomycete fungi (mainly Sordariomycetes), with no increment in potential plant-pathogenic fungi. Overall, our results point at a good perspective to use woody materials as sustainable soil improver via stimulation of saprotrophic fungi.

Formation of satellite uredinia as an important trait related to grapevine colonization by Phakopsora meliosmae‐myrianthae

Phakopsora meliosmae‐myrianthae, the causal agent of Asian grapevine leaf rust, significantly reduces the photosynthetic efficiency of grapevine leaves in green symptomless tissues surrounding lesions. This study took a close look at grapevine leaf colonization kinetics by P. meliosmae‐myrianthae and compared it to P. pachyrhizi–soybean and Uromyces appendiculatus–bean colonization. It is already known from the literature that soybean rust, similar to grapevine rust, has a negative effect on leaf photosynthesis greater than would be expected based on visual lesions. However, in contrast to soybean and grapevine rusts, the effect of bean rust on leaf photosynthesis is proportional to the diseased leaf area. Colonization progress was monitored by fungal biomass assessed via histological staining and quantitative polymerase chain reaction (qPCR). Individual lesions of P. meliosmae‐myrianthae on grapevine, P. pachyrhizi on soybean and U. appendiculatus on common bean leaves were evaluated every 3–4 days, and the number of uredinia was counted. Staining showed that mycelial colonization did not extend beyond the lesion border. The number of P. pachyrhizi and P. meliosmae‐myrianthae uredinia within the lesions increased over time (on average 14‐fold), whereas the number of U. appendiculatus uredinia remained the same. These findings were corroborated by qPCR, which revealed a greater increase in fungal biomass for Phakopsora spp. than for U. appendiculatus until 12 days post‐inoculation. The high number of satellite uredinia within lesions might be directly related to the impact of this pathogen in photosynthetic efficiency on symptomless areas of diseased grapevine leaves. This study identified accelerated formation of satellite uredinia as an important feature of grapevine colonization by P. meliosmae‐myrianthae.

Tree litter identity and predator density control prey and predator demographic parameters in a Mediterranean litter-based multi-trophic system

Plant litter decomposition is an essential process of ecosystem functioning, driven by a complex soil food web. The identity and density of the predators, as well as the quality and quantity of litter, could conjointly affect the strength of trophic interactions within a soil food web. Pine and oak are dominant tree species in temperate and Mediterranean forests and, although they exhibit distinct litter characteristics, no previous study attempted to decipher how these two litters can affect a litter-based multi-trophic system with varying predator density. Using a microcosm experiment, we aimed at understanding how different densities of a predatory Acari (Stratiolaelaps scimitus) and two Mediterranean litter species (Quercus pubescens and Pinus halepensis) may impact the demographic parameters of the predatory Acari, its Collembola prey (Folsomia candida) and the fungal biomass associated with litter. We did not observe any interactive effect of litter identity and predator density on both predator and prey demographic parameters. Survival and fecundity rates of the predator and its prey decreased at high predator density. However, demographic parameters of the predator and its prey were differentially affected by litter identity, with greater prey demographic parameters in Quercus litter and, in the opposite, greater predator demographic parameters in Pinus litter, probably due to differences in physical characteristics providing more or less refuge for the prey. We also observed a higher increase in fungal biomass in Pinus compared to Quercus litter, i.e. the litter with the fungivorous Collembola abundance reduced by the predatory Acari. Litter identity could thus strongly regulate these tri-trophic interactions (Fungi – fungivorous Collembola – predatory Acari) in forest ecosystems. Finally, the implications of our findings could be important as the distribution area of oak and pine forests may be altered in response to climate change with then potentially strong cascading effects on soil organisms and the processes they drive.

Intensifying rotations increases soil carbon, fungi, and aggregation in semi-arid agroecosystems

Increasing soil organic carbon (SOC) is a critical but daunting challenge in semi-arid agroecosystems. For dryland farmers, low levels of SOC and aggregation exacerbate the risks of farming in a water-limited environment − risks that will compound with climate change. Many dryland farmers in semi-arid climates use year long periods called summer fallow, where no crops are grown and weeds are controlled, to store rainwater and increase the yield of the following crop. In semi-arid climates around the world, dryland farmers are increasingly replacing summer fallow with a crop, a form of cropping system intensification. Cropping system intensification has the potential to increase SOC, but the drivers of this effect are unclear, and may change based on environmental conditions and management strategy. We quantified SOC, water-stable aggregates, and fungal and microbial biomass on 96 dryland, no-till fields in the semi-arid Great Plains, USA, representing three levels of cropping system intensity from wheat-fallow to continuous (no summer fallow) rotations along a potential evapotranspiration gradient. Cropping system intensity was positively associated with SOC, aggregation, and fungal biomass, and these effects were robust amidst variability in environmental and management factors. Continuous rotations averaged 1.28% SOC at 0–10 cm and had 17% and 12% higher SOC concentrations than wheat-fallow in 0–10 cm and 0–20 cm depths, respectively. Aggregate stability in continuous rotations was about twice that in wheat-fallow rotations. Fungal biomass was three times greater in continuous rotations than wheat-fallow, but was not significantly different from mid-intensity rotations. Using structural equation modeling, we observed that continuous cropping, potential evapotranspiration, % clay content, and fungal biomass together explained 50% of the variability in SOC, and that SOC appears to enhance aggregation directly and as mediated through increases in fungal biomass. Overall, the model suggests that cropping system intensity increases SOC both directly, through greater C inputs to soil, and indirectly, by increasing fungal biomass and aggregation. Our findings suggest that continuous cropping has the potential to provide gains in SOC and soil structure that will help offset C emissions and enhance the resilience of dryland agroecosystems.

Physiological Peculiarities of Lignin-Modifying Enzyme Production by the White-Rot Basidiomycete Coriolopsis gallica Strain BCC 142.

Sixteen white-rot Basidiomycota isolates were screened for production of lignin-modifying enzymes (LME) in glycerol- and mandarin peel-containing media. In the synthetic medium, Cerrena unicolor strains were the only high laccase (Lac) (3.2–9.4 U/mL) and manganese peroxidase (MnP) (0.56–1.64 U/mL) producers while one isolate Coriolopsis gallica was the only lignin peroxidase (LiP) (0.07 U/mL) producer. Addition of mandarin peels to the synthetic medium promoted Lac production either due to an increase in fungal biomass (Funalia trogii, Trametes hirsuta, and T. versicolor) or enhancement of enzyme production (C. unicolor, Merulius tremellosus, Phlebia radiata, Trametes ochracea). Mandarin peels favored enhanced MnP and LiP secretion by the majority of the tested fungi. The ability of LiP activity production by C. gallica, C. unicolor, F. trogii, T. ochracea, and T. zonatus in the medium containing mandarin-peels was reported for the first time. Several factors, such as supplementation of the nutrient medium with a variety of lignocellulosic materials, nitrogen source or surfactant (Tween 80, Triton X-100) significantly influenced production of LME by a novel strain of C. gallica. Moreover, C. gallica was found to be a promising LME producer with a potential for an easy scale up cultivation in a bioreactor and high enzyme yields (Lac-9.4 U/mL, MnP-0.31 U/mL, LiP-0.45 U/mL).

Responses of rice paddy micro-food webs to elevated CO2 are modulated by nitrogen fertilization and crop cultivars

Elevated atmospheric CO2 concentrations (eCO2) often increase plant growth but simultaneously lead to the nitrogen (N) limitation in soil. The corresponding mitigation strategy such as supplementing N fertilizer and growing high-yielding cultivars at eCO2 would further modify soil ecosystem structure and function. Little attention has, however, been directed toward assessing the responses of soil food web. We report results from a long-term free air CO2 enrichment (FACE) experiment in a rice paddy agroecosystem that examined the responses of soil micro-food webs to eCO2 and exogenous nitrogen fertilization (eN) in the rhizosphere of two rice cultivars with distinctly weak and strong responses to eCO2. Soil micro-food web parameters, including microfauna (protists and nematodes) and soil microbes (bacteria and fungi from phospholipid fatty acid (PLFA) analysis), as well as soil C and N variables, were determined at the heading and ripening stages of rice. Results showed that eCO2 effects on soil micro-food webs depended strongly on N fertilization, rice cultivar and growth stage. eCO2 stimulated the fungal energy channel at the ripening stage, as evidenced by increases in fungal biomass (32%), fungi:bacteria ratio (18%) and the abundance of fungivorous nematodes (64%), mainly due to an enhanced carbon input. The eN fueled the bacterial energy channel by increasing the abundance of flagellates and bacterivorous nematodes, likely through alleviating the N-limitation of plants and rhizosphere under eCO2. While eCO2 decreased the abundance of herbivorous nematodes under the weak-responsive cultivar by 59% and 47% with eN at the heading and ripening stage, respectively, the numbers of herbivorous nematodes almost tripled (×2.9; heading) and doubled (×1.6; ripening) under the strong-responsive cultivar with eCO2 at eN due to higher root quantity and quality. Structural equation model (SEM) showed that lower trophic-level organisms were affected by bottom-up forces of altered soil resources induced by eCO2 and eN, and effects on higher trophic level organisms were driven by bottom-up cascades with 69% of the variation being explained. Taken together, strategies to adapt climate change by growing high-yielding crop cultivars under eCO2 may face a trade-off by negative soil feedbacks through the accumulation of root-feeding crop pest species.

Soil networks become more connected and take up more carbon as nature restoration progresses

Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.

Utilisation of Jatropha press cake as substrate in biomass and lipase production from Aspergillus niger 65I6 and Rhizomucor miehei CBS 360.62

Jatropha curcas L. is a tropical plant that grows well on poor soils in arid regions and produces oil-rich, unedible seeds. The oil from these seeds can be used in the production of biodiesel. In addition, the press-cake waste that is left after oil extraction contains approximately 40% of protein. The use of Jatropha press-cake as substrate for fungal growth and the production of lipase by Aspergillus niger 65I6 isolated from Indonesia and Rhizomucor miehei CBS 260.62 was investigated. Hydrolysis of the press-cake using 2.5% sodium hydroxide for 45 min was found to be the best pre-treatment method indicated by a high lipase activity. The alkaline hydrolysis increased the amount of reducing sugars and soluble protein to 133.3% and 40% of the initial amount, respectively. 5.7% of the protein fraction was hydrolysed by the alkaline pretreatment. The alkaline hydrolysed Jatropha press-cake was used as a growth substrate for A. niger 65I6 and R. miehei CBS 360.62. Both fungi grew well on the hydrolysed press cake. The addition of glucose or maltodextrin gave a substantial increase in fungal biomass but inhibited the lipase production, very likely due to catabolite repression by the sugars.

Geography and agronomical practices drive diversification of the epiphytic mycoflora associated with barley and its malt end product in western Canada

The microbiome associated with cereal grain includes a mycoflora, which often reflects the environmental conditions that host plants have been cultivated under. Some of these factors can affect grain safety and quality impeding global trade or end use of agricultural commodities. This study applied 454 pyrosequencing to the internal transcribed spacer of rDNA to investigate effects of harvest methods and dates on the epiphytic mycoflora naturally associated with barley seeds. A total of 64 barley samples grown at six locations across western Canada were collected in two growing seasons (2011 and 2012). Of these, eight barley samples harvested in 2011 were further processed and malted before amplicon-based metagenomic analysis of the microbiome. A total of 885,084 ITS1 and 618,265 ITS2 sequences were clustered into 754 and 769 operational taxonomic units at 97% similarity cut-off, respectively, and classified against the curated UNITE fungal ITS reference database. Between 76–275 ITS1 and 51–260 ITS2 fungal OTUs were observed for each sample, respectively. The core fungal community consisted of wide spread yeast or yeast-like fungi (e.g. Cryptococcus) and genera containing species commonly known to be associated with plants (e.g. Alternaria, Epicoccum) including important pathogens such as Fusarium spp. and Pleospora spp. Geographic location of the field stations was identified as the determining factor best explaining the observed differences in the fungal communities on harvested barley in western Canada. Agronomical practices, namely swathing and timely harvest helped to reduce some of the microbial load on barley grain. Further processing through malting favored the development of certain fungal genera, with an increase of fungal biomass associated with Fusarium and Alternaria spp. This could have negative effects on end use quality, indicating a need for managing the risk of fungal contaminations more proactively.

Microbial growth and community structure in acid mine soils after addition of different amendments for soil reclamation

The extreme soil conditions in metalliferous mine soils have a negative influence on soil biological activity. Therefore, amendments are often used to improve soil quality and activate microbial communities. In order to elucidate some of the factors controlling microbial growth and community structure after application of amendments in acid mine soils, we performed an incubation experiment with four amendments: pig slurry (PS), pig manure (PM) and pyrogenic carbonaceous material (PCM), applied with and without marble waste (MW; CaCO3). Results showed that PM and PCM (alone or together with MW) contributed to an important increase in recalcitrant organic C, C/N ratio and aggregate stability. All the treatments, except PS without MW increased soil pH above six resulting in the partial immobilization of the metals. Bacterial and fungal growths were highly dependent on pH and labile organic C. Pig slurry supported the highest microbial growth: applied alone stimulated fungal growth, whereas applied with MW stimulated bacterial growth. Pyrogenic carbonaceous material provoked the lowest microbial growth, especially for fungi, with no significant increase in fungal biomass. MW+PCM increased bacterial growth up to values similar to PM and MW+PM, suggesting that, at least in the short term, part of the PCM was degraded, and mainly by bacteria rather than fungi. PM, MW+PS and MW+PM supported the highest microbial biomass and a similar community structure, related with the presence of high organic C concentrations and high pH, with immobilization of metals and increased soil quality. PCM contributed to improved soil structure, increased recalcitrant organic C, and decreased metal mobility, with low stimulation of microbial growth. Thus, in order to activate microbial populations in reclaimed mine soils, a source of labile organic compounds should be included in the management plan of the area.

Effects of climate change on leaf breakdown by microorganisms and the shredder Phylloicus elektoros (Trichoptera: Calamoceratidae)

Climate change may affect species diversity and, consequently, ecological processes such as leaf decomposition. We evaluated the effects of increased temperature and carbon dioxide (CO2) on fungal biomass, leaf breakdown, and on survival and growth of the shredder Phylloicus elektoros. We hypothesized that climatic changes would result in lower survival and growth of shredders and lower leaf consumption by these organisms. On the other hand, we predicted an increase in fungal biomass in response to climatic changes. We conducted an experiment in Manaus, Brazil, using four microcosms that simulate real-time air temperature and CO2 (control chamber), as well as three other chambers subjected to fixed increases in temperature and CO2 as compared to the control chamber. The “extreme” condition represented an increase of ~4.5°C in temperature and ~870 ppm in CO2 in relation to the control chamber. Total and shredder leaf-breakdown rates, fungal biomass, and shredder survival rates were significantly lower in warmer and CO2 concentrated atmospheres. Shredder growth rate and leaf breakdown by microorganisms were similar among all climatic conditions. With climatic changes, we found an increase in the relative importance of microorganisms on leaf-breakdown rates as compared to shredders. Thus, lower leaf breakdown and a change in the main decomposer due to future climatic conditions may result in major changes in the pathways of organic matter processing and, consequently, in aquatic food webs.

Influence of streambed substratum composition on stream microbial communities exposed to the fungicide tebuconazole

Summary Fungicides reaching stream ecosystems have different capacities to adsorb to benthic substrata and thus cause varying effects on benthic microbial communities. We evaluated the potential of a triazole fungicide, tebuconazole (TBZ), to adsorb to submerged leaves and sand and assessed TBZ effects on sand‐ and leaf‐associated microbial communities. An indoor stream channel experiment was designed to test TBZ effects slightly above concentrations measured in agricultural streams (10.7 ± 0.3 μg L−1) on the microbial communities associated with either submerged leaves alone, sand alone or a mixed substratum of leaves + sand over 5 weeks. Weekly samples were taken to determine TBZ effects on the biomass and activity (litter breakdown rate, fungal sporulation rate and extracellular enzyme activities) of fungi and bacteria as well as the dissipation of TBZ in stream channels. TBZ significantly reduced fungal biomass (17–20% relative to controls) but increased bacterial biomass (34–50%) on leaves and sand incubated separately. TBZ also significantly inhibited phenol oxidase activity (36%) in sand but not in leaves. Differences in TBZ effects between leaves and sand communities were not explained by differences between substrata in TBZ adsorption but more likely were related to differences in biomass accrual and structure of the microbial communities. Mixing leaves+sand tended to attenuate TBZ effects on microbial communities, which was probably explained by a greater surface area available for TBZ adsorption to the substrata. This hypothesis is supported by the greater TBZ dissipation in stream channels receiving both leaves and sand. However, leaf and sand mixtures not only diluted but also modified TBZ effects on sand communities (14% increase in fungal biomass and 82% increase in the sporulation of aquatic hyphomycetes). This result suggests that sand could serve as a refuge for fungi during TBZ‐contamination episodes. Our study points to the importance of substratum heterogeneity for the ecotoxicological effects of TBZ on agricultural streams and highlights the contrasting responses of fungi and bacteria to contamination by a widespread fungicide.