Sporulation Of Aquatic Hyphomycetes Research Articles

Fungal endophyte‐infected leaf litter alters in‐stream microbial communities and negatively influences aquatic fungal sporulation

Endophytes are ubiquitous plant‐associated microbes and although they have the potential to alter the decomposition of infected leaf litter, this has not been well‐studied. The endophyte Rhytisma punctatum infects the leaves of Acer macrophyllum (bigleaf maple), causing the appearance of black ‘tar spots’ that persist in senesced leaves. Other foliar fungi also cause visible damage in healthy tissues of this host plant system including an unidentified bullseye‐shaped lesion, common in western Washington. Using three treatments of endophyte infection status in leaf tissue (R. punctatum‐infected, bullseye‐infected, lesion‐free), leaf litter discs were submerged in a third‐order temperate stream using mesh litter bags and harvested periodically over two months to determine the effects of litter treatment and incubation time on litter mass loss, fungal sporulation, and microbial community colonization. Litter containing symptomatic endophyte infections (Rhytisma or bullseye) had reduced sporulation of aquatic hyphomycetes, but decomposed significantly faster than lesion‐free or bullseye‐infected litter. Using amplicon‐based sequencing, we found a significant difference in bacterial communities colonizing Rhytisma‐infected and bullseye‐infected leaf litter, a significant difference in fungal communities colonizing Rhytisma‐infected leaf litter compared to the two other treatments, and a change in both community structure and relative abundances of bacterial and fungal taxa throughout the study period. Indicator Species Analysis clarified the drivers of these community shifts at the genus level. Our results show that endophyte‐associated, in‐stream sporulation and microbial community effects are observable within one species of leaf litter.

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.

Influence of leaf quality in microbial decomposition in a headwater stream in the Brazilian cerrado: a 1-year study.

The temporal dynamics of leaf decomposition in a tropical stream were evaluated by measuring the input of leaves from riparian vegetation. The resulting mixture of leaves was processed by decomposer microorganisms and, in particular, by aquatic hyphomycetes, the most important microorganisms associated with leaf litter decomposition. Leaf decomposition and the characteristics and activity of the microbial community were investigated over the course of 1 year; these parameters depended on the composition and availability of leaves in the stream. We assessed the biomass, activity, and community structure of the fungi associated with the decomposing leaf mixtures monthly in a tropical stream with little seasonal variation in water characteristics. The leaf material included 27 riparian species; the amount of leaves of each contributing species varied from month to month, with higher overall values in the rainy season. Leaf decomposition was slow, and leaf mass loss did not occur monthly; however, leaf mass loss was significantly lower in May and September. The values of ATP, the ergosterol concentration, and the sporulation of aquatic hyphomycetes varied during the experiment, and only the ergosterol concentration (fungal biomass) was correlated with leaf mass loss. The sporulation rates of aquatic hyphomycetes peaked at the beginning of the rainy season (October), when only three hyphomycete species were present out of the total of seven that were found during the year. In this tropical stream, where the physical and chemical characteristics of the stream water varied little during the year, we hypothesize that changes related to leaf chemical composition could be the cause of changes in decomposition and the abundance and composition of the fungal assemblages. No significant differences were found for the parameters analyzed (lignin, cellulose, fiber, phosphorous, and polyphenols).

Tar-spot infection delays fungal colonization and decomposition of maple leaves

Tar spot is a common leaf disease of Acer caused by Rhytisma spp. (Ascomycetes). Initial symptoms are small green-yellow spots. These infected areas turn into black fungal stromata, which resemble blobs of tar. Stromata with apothecia overwinter and release ascospores in the following spring. We measured rates of decomposition of leaf litter of infected and uninfected Norway maple (Acer platanoides). In addition, we assessed changes in leaf-litter N and P and rates of sporulation of aquatic hyphomycetes. We incubated leaf disks from areas covered with tar spot, disks touching but not overlapping with tar spot (adjacent disks), and disks from uninfected leaves in a stream. The exponential decay rate of uninfected disks was 50% greater than those for infected and adjacent disks. Initial N and P concentrations were highest in infected disks. N and P concentrations dropped in all treatments during the 1st wk in the stream and subsequently increased. Conidium release by aquatic hyphomycetes in the laboratory was lowest from infected disks and highest from uninfected disks. Cumulative sporulation over 10 wk of stream exposure increased from infected (109 conidia mg−1 d−1) to adjacent (215 conidia mg−1 d−1) to uninfected (521 conidia mg−1 d−1) disks. Similarity of fungal communities was highest between adjacent and uninfected disks (71.5%) and lowest between infected and uninfected leaves (51.9%).

Stimulation of leaf litter decomposition and associated fungi and invertebrates by moderate eutrophication: implications for stream assessment

Summary1. We investigated the effect of moderate eutrophication on leaf litter decomposition and associated invertebrates in five reference and five eutrophied streams in central Portugal. Fungal parameters and litter N and P dynamics were followed in one pair of streams. Benthic invertebrate parameters that are considered useful in bioassessment were estimated in all streams. Finally, we evaluated the utility of decomposition as a tool to assess stream ecosystem functional integrity.2. Decomposition of alder and oak leaves in coarse mesh bags was on average 2.3–2.7× faster in eutrophied than in reference streams. This was attributed to stimulation of fungal activity (fungal biomass accrual and sporulation of aquatic hyphomycetes) by dissolved nutrients. These effects were more pronounced for oak litter (lower quality substrate) than alder. N content of leaf litter did not differ between stream types, while P accrual was higher in the eutrophied than in the reference stream. Total invertebrate abundances and richness associated with oak litter, but not with alder, were higher in eutrophied streams.3. We found only positive correlations between stream nutrients (DIN and SRP) and leaf litter decomposition rates in both fine and coarse mesh bags, associated sporulation rates of aquatic hyphomycetes and, in some cases, total invertebrate abundances and richness.4. Some metrics based on benthic invertebrate community data (e.g. % shredders, % shredder taxa) were significantly lower in eutrophied than in reference streams, whereas the IBMWP index that is specifically designed for the Iberian peninsula classified all 10 streams in the highest possible class as having ‘very good’ ecological conditions.5. Leaf litter decomposition was sufficiently sensitive to respond to low levels of eutrophication and could be a useful functional measure to complement assessment programmes based on structural parameters.

Whole-stream nitrate addition affects litter decomposition and associated fungi but not invertebrates

We assessed the effect of whole-stream nitrate enrichment on decomposition of three substrates differing in nutrient quality (alder and oak leaves and balsa veneers) and associated fungi and invertebrates. During the 3-month nitrate enrichment of a headwater stream in central Portugal, litter was incubated in the reference site (mean NO3-N 82 microg l-1) and four enriched sites along the nitrate gradient (214-983 microg NO3-N l-1). A similar decomposition experiment was also carried out in the same sites at ambient nutrient conditions the following year (33-104 microg NO3-N l-1). Decomposition rates and sporulation of aquatic hyphomycetes associated with litter were determined in both experiments, whereas N and P content of litter, associated fungal biomass and invertebrates were followed only during the nitrate addition experiment. Nitrate enrichment stimulated decomposition of oak leaves and balsa veneers, fungal biomass accrual on alder leaves and balsa veneers and sporulation of aquatic hyphomycetes on all substrates. Nitrate concentration in stream water showed a strong asymptotic relationship (Michaelis-Menten-type saturation model) with temperature-adjusted decomposition rates and percentage initial litter mass converted into aquatic hyphomycete conidia for all substrates. Fungal communities did not differ significantly among sites but some species showed substrate preferences. Nevertheless, certain species were sensitive to nitrogen concentration in water by increasing or decreasing their sporulation rate accordingly. N and P content of litter and abundances or richness of litter-associated invertebrates were not affected by nitrate addition. It appears that microbial nitrogen demands can be met at relatively low levels of dissolved nitrate, suggesting that even minor increases in nitrogen in streams due to, e.g., anthropogenic eutrophication may lead to significant shifts in microbial dynamics and ecosystem functioning.

Effects of temperature and light on growth and sporulation of aquatic hyphomycetes

Nine isolates of the aquatic hyphomycetes Dactylella aquatica, Flagellospora penicillioides, Flagellospora saccata, Helicomyces sp., Lunulospora curvula, Phalangispora constricta, Tetracladium setigerum, Vermispora cauveriana and Wiesneriomyces laurinus were incubated at different temperatures (5–35 °C) to study their growth on MEA medium. Maximum growth was observed between 20 and 30 °C. Growth rate was highest in Vermispora cauveriana and lowest in Tetracladium setigerum. Colonies on submerged leaves showed maximum spore production at 25 °C. Light was confirmed as a stimulus to sporulation.

Leaf Breakdown in Streams of an Alpine Glacial Floodplain: Dynamics of Fungi and Nutrients

Breakdown, fungal colonization, and nutrient dynamics of green alder (Alnus viridis) leaves were examined in 4 stream types of a glacial alpine floodplain in southeast Switzerland. Standardized leaf packs were enclosed in both fine- and coarse-mesh bags to differentiate between microbial and other processes contributing to leaf mass loss. Fungal biomass was quantified from ergosterol concentrations. Apart from 1 site where shredder consumption of leaves greatly accelerated leaf mass loss, exponential breakdown coefficients (k) ranged from -0.0029 to -0.0064 d -1 , indicating that leaf breakdown proceeded at a relatively slow but significant rate. Fungal biomass in decomposing leaves attained levels (>500 μg ergosterol/g litter dry mass) as high as those found in temperate woodland streams. Sporulation of aquatic hyphomycetes on leaves was detectable in all stream types (up to 700 conidia mg -1 litter dry mass d -1 ), although it was depressed at the 2 sites nearest the glacier ...

Temperature and Sporulation of Aquatic Hyphomycetes

Temperature appears to be an important factor affecting the occurrence and distribution of aquatic hyphomycetes, the dominant leaf litter-decomposing fungi in streams. We compared conidium production by eight species of aquatic hyphomycetes grown on yellow poplar leaves in stream-simulating microcosms at three temperatures (15, 20, and 25 degrees C). The greatest conidium production occurred at 15 degrees C for one species, 20 degrees C for two species, and 25 degrees C for two species. Two species produced similar numbers of conidia at 20 and 25 degrees C, and one species produced similar numbers of conidia at all three temperatures. Linear growth rates were determined on malt extract agar. Six species had the same pattern of temperature responses for growth on malt extract agar as for sporulation on leaves, as shown by the positive correlations between the two parameters at the three temperatures. The species examined also exhibited differences in number of conidia produced from a similar amount of leaf material at a given temperature. These differences appeared to be due primarily to differences in individual conidium mass (determined by weighing conidia produced from cultures), as shown by the relationship of the type Y = k/X (r = 0.96), where Y is the number of conidia produced, X is the individual conidium mass in milligrams, and k is a constant empirically determined to be 2.11. This finding supports the hypothesis that aquatic hyphomycetes allocate similar amounts of their resources to reproduction but vary with respect how these resources are partitioned into reproductive units (conidia).

Effects of aluminium in acid streams on growth and sporulation of aquatic hyphomycetes

We investigated, by field and laboratory experiments, the effects of aluminium in an acid stream (pH 5.0) on the growth and sporulation of aquatic hyphomycete fungi which degrade organic litter. The stream water had monomeric aluminium (Al m) concentrations of 9.1–13.4 μ m — fifty times higher than a nearby circumneutral stream. Alder leaves submersed in the stream accumulated Al, most of which was tightly bound. Growth rates of four species of aquatic hyphomycetes were altered by inclusion of Al m in the culture medium. On a polypectate substrate, and on low-phosphate medium with glucose, growth rates increased significantly. On a low-nutrient substrate of homogenized alder leaves, growth rates were inhibited by aluminium. The pattern of mycelial growth was found to be different on a polypectate medium including Al m, compared with a control without aluminium. There was a significant increase in hyphal radial growth and a decrease in the hyphal growth unit. The effect resembled the growth of a starved fungal colony. Treatment with Al m decreased pectinase production by the four fungal species tested. The capacity of these species to sporulate was reduced by flooding culture plates with Al m solution. These deleterious metabolic effects were most severe in isolates taken from circumneutral streams and less marked, though significant, in species originating from acid streams.

Relationships between growth and sporulation of aquatic hyphomycetes on decomposing leaf litter

The dynamics of changes in microbial biomass (ATP concentrations), respiration rates and sporulation rates of aquatic hyphomycetes associated with tulip poplar leaf disks in two streams with different water chemistry were compared with the activities of a dominant fungal species from each stream growing on sterilized leaf disks in the laboratory. Aquatic hyphomycetes sporulated at maximum rates after 15–19 d in both stream and laboratory studies. Sporulation occurred during periods of increasing biomass and respiration indicating a close relationship between growth and sporulation in these fungi. Leaf disks decomposing in the hardwater stream supported greater biomass, activity and number of species than those decomposing in the softwaer stream. Fungi colonizing leaf disks in the laboratory exhibited higher ATP concentrations and sporulation rates than the communities from either stream. These differences appear to be related to water chemistry, particularly N and P concentrations. Organic matter budgets calculated for the two species grown in the laboratory indicated that growth yield coefficients were 0·15–0·23 g g −1 and net production efficiencies ranged from 24 to 46 %. A significant portion of fungal production was converted into conidia by both fungi.

Further studies of sporulation of aquatic hyphomycetes in relation to aeration

The effect of forced aeration in stimulating sporulation in aquatic Hyphomycetes is interpreted as due to two phenomena. The time taken for spore development and detachment is several hours shorter at high aeration rates than at low aeration rates. The number of conidiophores per unit area of culture surface is significantly greater at high aeration rates. This is probably due to increased hyphal branching induced by turbulence. Cultures which have been induced to form higher numbers of conidia by rapid aeration continue to do so when the aeration rate is decreased.

Sporulation of aquatic hyphomycetes in relation to aeration

Sporulation of aquatic hyphomycetes is stimulated if pieces of agar cultures are placed in water and forcibly aerated using compressed air. Increasing the rate of aeration from 100 ml/min to 1000 ml/min resulted in increased spore production. Only slight differences were detected in the concentration of dissolved oxygen in the culture bottles at these different aeration rates. Experiments using gas mixtures which result in different levels of dissolved oxygen in the cultures indicate that enhanced sporulation at high aeration rates is unlikely to be related to oxygen concentration. No evidence was found to suggest the existence of a volatile sporulation inhibitor removed from cultures at high aeration rates. Significantly more spores were produced in cultures aerated using a hypodermic needle than when using a sintered glass bulb, and it is suggested that this effect may be correlated with the greater turbulence in cultures aerated through a hypodermic needle. Experiments using stirred aerated cultures show that sporulation is related to stirring rate. It is concluded that the enhanced sporulation which results from forcible aeration is related to the mechanical effects of increasing turbulence.