The Effect of the Herbicide Mecoprop on Heliscus lugdunensis and Its Influence on the Preferential Feeding of Gammarus Pseudolimnaeus

Abstract Exposure of the aquatic hyphomycete Heliscus lugdunensis to the herbicide Mecoprop did not significantly affect production of the antigen recognized by the specific monoclonal antibody NG-CF10. Therefore, an ELISA method, developed in a previous study, could be used to quantify the biomass of H. lugdunensis colonizing leaves exposed to this herbicide. Exposure to Mecoprop significantly reduced the mycelial biomass associated with alder leaves. This was shown to be a threshold response rather than a dose response, with higher biomass recorded on control leaves. No significant differences were found over the range of Mecoprop concentrations used. In laboratory experiments, Gammarus pseudolimnaeus was offered a choice of alder leaves exposed to a range of Mecoprop concentrations. The animals were able to discriminate between the exposed and control leaves, and between inoculated and sterile leaves. Presence of the fungus resulted in increased leaf consumption, but no interaction between the Mecoprop concentrations and fungal colonization was observed. The major factor affecting food choice was the concentration of Mecoprop that the leaves were exposed to—not the Mecoprop-mediated effects on fungal biomass. Received: 10 February 1997; Accepted: 8 May 1997     

Leaf Barriers to Fungal Colonization and Shredders (Tipula lateralis) Consumption of Decomposing Eucalyptus globulus

Abstract Herein we assess the importance of leaf cuticle, polyphenolic, and essential oils contents of Eucalyptus globulus leaves to hyphomycete colonization and shredder consumption. Optical and electron microscopy revealed that, at least during the first 5 weeks of conditioning, the cuticle remains virtually intact. Stomata provide the main access for hyphae to internal leaf tissues and, eventually, for spore release. We suggest that in E. globulus leaves, fungal decomposition progresses predominantly in and from the eucalyptus leaf mesophyll to the outside. Malt extract agar media supplemented with either eucalyptus essential oils or tannic acid completely inhibited (Articulospora tetracladia, Lemonniera aquatica, and Tricladium gracile) or depressed (Heliscus lugdunensis, Lunulospora curvula, and Tricladium angulatum) aquatic hyphomycetes growth. The transference of both secondary compounds to alder leaves induced similar and significant reduction in Tipula lateralis larval consumption. Results consistently indicate that eucalyptus oils are stronger deterrents than polyphenols. The waxy cuticle of E. globulus appears to be a key physical factor delaying fungal colonization during decomposition. We hypothesize that the relative influence of leaf phenols and essential oils to aquatic hyphomycetes and shredders may be related to three main factors: (a) initial distribution of such compounds in the leaves; (b) possibility of their decrease through decomposition; and (c) consumption strategies of detritivores. Received: 8 July 1998; Accepted: 21 December 1998     

Aquatic hyphomycete diversity and identity affect leaf litter decomposition in microcosms

We conducted a microcosm experiment with monocultures and all possible combinations of four aquatic hyphomycete species, Articulospora tetracladia, Flagellospora curta, Geniculospora grandis and Heliscus submersus, to examine the potential effects of species richness on three functional aspects: leaf litter decomposition (leaf mass loss), fungal production (ergosterol buildup) and reproductive effort (released spores). Both species richness and identity significantly affected fungal biomass and conidial production (number and biomass of released spores), whereas only species identity had a significant effect on leaf mass loss. In mixed cultures, all measures of fungal functions were greater than expected from the weighted performances of participating species in monoculture. Mixed cultures outperformed the most active monoculture for biomass accumulation but not for leaf mass loss and conidial production. The three examined aspects of aquatic hyphomycete activity tended to increase with species richness, and a complementary effect was unequivocally demonstrated for fungal biomass. Our results also suggest that specific traits of certain species may have a greater influence on ecosystem functioning than species number.     

Leaf litter decomposition and microbial activity in nutrient-enriched and unaltered reaches of a headwater stream

SUMMARY 1. Decomposition of red maple ( Acer rubrum ) and rhododendron ( Rhododendron maximum ) leaves and activity of associated microorganisms were compared in two reaches of a headwater stream in Coweeta Hydrologic Laboratory, NC, U.S.A. The downstream reach was enriched with ammonium, nitrate, and phosphate whereas the upstream reach was not altered.
2. Decomposition rate, microbial respiration, fungal and bacterial biomass, and the sporulation rate of aquatic hyphomycetes associated with decomposing leaf material were significantly higher for both leaf types in the nutrient-enriched reach. Species richness and community structure of aquatic hyphomycetes also exhibited considerable changes with an increase in the number of fungal codominants in the nutrient-enriched reach.
3. Fungal biomass was one to two orders of magnitude greater than bacterial biomass in both reaches. Changes in microbial respiration rate corresponded to those in fungal biomass and sporulation, suggesting a primary role of fungi in leaf decomposition.
4. Nutrient enrichment increased microbial activity, the proportion of leaf carbon channelled through the microbial compartment and the decomposition rate of leaf litter.     

Contribution of fungal biomass to the growth of the shredder, Pycnopsyche gentilis (Trichoptera: Limnephilidae)

1.  1. It has been accepted that aquatic hyphomycetes colonising submerged leaves increase the nutritional value of leaf detritus and suggested that fungal biomass plays a greater role in the growth of shredders than leaf tissue itself. However, it is not clear what proportion of the nutritional needs of shredders is met by fungal biomass.
2.  We fed Pycnopsyche gentilis larvae with tulip poplar ( Liriodendron tulipifera ) leaf discs colonised by the aquatic hyphomycete, Anguillospora filiformis , which had been radiolabelled to quantify the contribution of fungal carbon to the growth of the shredder at different larval developmental stages. Instantaneous growth rates of larvae on this diet were also estimated.
3.  When provided with fungal-colonised leaves (14–16% fungal biomass), the third and the fifth instar larvae of P. gentilis grew at the rates of 0.061 and 0.034 day⁻¹, respectively, but on a diet of sterile leaves, both larval instars lost weight. The incorporation rates of fungal carbon were 31.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 100% of the daily growth rate of the third instar larvae and 8.6 μg C mg⁻¹ AFDM day⁻¹, accounting for 50% of the daily growth rate of the fifth instar larvae.
4.  These results suggest that leaf material colonised by A. filiformis is a high quality food resource for P. gentilis larvae, and that fungal biomass can contribute significantly to the growth of these larvae. Differences in feeding behaviour and digestive physiology may explain the significantly greater assimilation of fungal biomass by the earlier instar than the final instar. To satisfy their nutritional needs the fifth instar larvae would have to assimilate detrital mass that may have been modified by fungal exoenzymes.     

Surprising spectra of root-associated fungi in submerged aquatic plants

Similarly to plants from terrestrial ecosystems, aquatic species harbour wide spectra of root-associated fungi (RAF). However, comparably less is known about fungal diversity in submerged roots. We assessed the incidence and diversity of RAF in submerged aquatic plants using microscopy, culture-dependent and culture-independent techniques. We studied RAF of five submerged isoetid species collected in four oligotrophic freshwater lakes in Norway. Levels of dark septate endophytes (DSE) colonization differed among the lakes and were positively related to the organic matter content and negatively related to pH. In total, we identified 41 fungal OTUs using culture-dependent and culture-independent techniques, belonging to Mucoromycotina, Chytridiomycota, Glomeromycota, Ascomycota as well as Basidiomycota. Sequences corresponding to aquatic hyphomycetes (e.g. Nectria lugdunensis, Tetracladium furcatum and Varicosporium elodeae) were obtained. Eight arbuscular mycorrhizal taxa belonging to the orders Archaeosporales, Diversisporales and Glomerales were also detected. However, the vast majority of the fungal species detected (e.g. Ceratobasidium sp., Cryptosporiopsis rhizophila, Leptodontidium orchidicola, and Tuber sp.) have previously been known only from roots of terrestrial plants. The abundance and phylogenetic distribution of mycorrhizal as well as nonmycorrhizal fungi in the roots of submerged plants have reshaped our views on the fungal diversity in aquatic environment.     

Effect of leaf litter characteristics on leaf conditioning and on consumption by Gammarus pulex

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Microbial impacts on plant-herbivore interactions: the indirect effects of a birch pathogen on a birch aphid

The role of indirect interactions in structuring communities is becoming increasingly recognised. Plant fungi can bring about changes in plant chemistry which may affect insect herbivores that share the same plant, and hence the two may interact indirectly. This study investigated the indirect effects of a fungal pathogen ( Marssonina betulae) of silver birch ( Betula pendula) on an aphid ( Euceraphis betulae), and the processes underpinning the interaction. There was a strong positive association between natural populations of the aphid and leaves bearing high fungal infection. In choice tests, significantly more aphids settled on leaves inoculated with the fungus than on asymptomatic leaves. Individual aphids reared on inoculated leaves were heavier, possessed longer hind tibiae and displayed enhanced embryo development compared with aphids reared on asymptomatic leaves; population growth rate was also positively correlated with fungal infection when groups of aphids were reared on inoculated branches. Changes in leaf chemistry were associated with fungal infection with inoculated leaves containing higher concentrations of free-amino acids. This may reflect a plant-initiated response to fungal attack in which free amino acids from the degradation of mesophyll cells are translocated out of infected leaves via the phloem. These changes in plant chemistry are similar to those occurring during leaf senescence, and are proposed as the mechanistic basis for the positive interaction between the fungus and aphid.     

Aquatic Hyphomycetes in Polluted Groundwater Habitats of Central Germany

Polluted groundwater wells located in a former copper shale mining district (11 sites; Mansfelder Land, Central Germany) and in meadows of the Mulde and Elbe rivers (2 sites) were assessed for occurrence and species richness of aquatic hyphomycetes. Water temperatures at all sites were relatively low and fluctuated less than in surface waters. Oxygen concentrations were always below saturation, whereas sulfate, nitrate, and phosphate levels reached extremely high values in several of the wells. Relatively high levels of Pb, Mn, and Fe were found in some of the wells, but overall few concentrations of individual metals and metalloids exceeded European guidelines for drinking water. Pollen tube growth inhibition, used to assess cytotoxicity of the water, ranged between 4 and 50%. Between 1 and 10 distinct species of aquatic hyphomycetes colonized sterile Alnus glutinosa leaves exposed at the Mansfelder Land sites; for the meadow sites, 8-20 species were found. Heliscus lugdunensis and Anguillospora sp. were the two most widespread species. Fungal colonization occurred much more slowly than in surface water, as demonstrated by scanning electron microscopy and the release of conidia from recovered leaves. The conidial output from exposed alder leaves ranged from 0.2 to 95 conidia mg (-1) dry mass, corresponding to 10% of the values for contaminated surface waters in the same region. Overall, groundwater appears to be a marginal habitat for aquatic hyphomycetes, but may nevertheless play a vital role as long-term reservoir facilitating rapid recolonization following a collapse in fungal communities in surface waters.     

Ergosterol-to-Biomass Conversion Factors for Aquatic Hyphomycetes

Fourteen strains of aquatic hyphomycete species that are common on decaying leaves in running waters were grown in liquid culture and analyzed for total ergosterol contents. Media included an aqueous extract from senescent alder leaves, a malt extract broth, and a glucose-mineral salt solution. Concentrations of ergosterol in fungal mycelium ranged from 2.3 to 11.5 mg/g of dry mass. The overall average was 5.5 mg/g. Differences among both species and growth media were highly significant but followed no systematic pattern. Stationary-phase mycelium had ergosterol contents 10 to 12% lower or higher than mycelium harvested during the growth phase, but these differences were only significant for one of four species examined. Availability of plant sterols in the growth medium had no clear effect on ergosterol concentrations in two species tested. To convert ergosterol contents determined in field samples to biomass values of aquatic hyphomycetes, a general multiplicative factor of 182 is proposed. More accurate estimates would be obtained with species-specific factors. Using these in combination with estimates of the proportion of the dominant species in a naturally established community on leaves resulted in biomass estimates that were typically 20% lower than those obtained with the general conversion factor. Improvements of estimates with species-specific factors may be limited, however, by intraspecific variability in fungal ergosterol content.     

Growth response of Afzelia africana Sm. seedlings to ectomycorrhizal inoculation in a nutrient-deficient soil

 The growth and mineral nutrition responses of seedlings of two provenances of Afzelia africana Sm. from Senegal and Burkina Faso, inoculated with four ectomycorrhizal (ECM) fungi (Scleroderma spp. and an unidentified isolate) from the same regions were assessed in a pot experiment in a savanna ECM-propagule-free soil deficient in NPK. There was little variation in the ability of the different fungal species to colonize roots of either provenance of A. africana or to produce external hyphal in soil. Root colonization by ECM fungi and their hyphal development were not related to mineral nutrition or ECM dependency. Differences in P, N, Mg and Ca concentrations in the leaves of inoculated and non-inoculated Afzelia seedlings were not always associated with production of biomass. Only leaf K concentration increased in both provenances after ECM inoculation. However, the Burkina Faso provenance responded better to inoculation with the two fungal isolates than the Senegal provenance in terms of biomass production. This was due to stimulation of root dry weight of the Burkina Faso provenance. Therefore, the hypothesis arises that non-nutritional rather than nutritional effects explain the contribution of ECM inoculation to the growth of A. africana seedlings. Accepted: 27 April 1999     

Sex-Related Responses of Populus cathayana Shoots and Roots to AM Fungi and Drought Stress

We investigated the impact of drought and arbuscular mycorrhizal (AM) fungi on the morphological structure and physiological function of shoots and roots of male and female seedlings of the dioecious plant Populus cathayana Rehder. Pot-grown seedlings were subjected to well watered or water-limiting conditions (drought) and were grown in soil that was either inoculated or not inoculated with the AM fungus Rhizophagus intraradices. No significant differences were found in the infection rates between the two sexes. Drought decreased root and shoot growth, biomass and root morphological characteristics, whereas superoxide radical (O₂–) and hydrogen peroxide content, peroxidase (POD) activity, malondialdehyde (MDA) concentration and proline content were significantly enhanced in both sexes. Male plants that formed an AM fungal symbiosis showed a significant increase in shoot and root morphological growth, increased proline content of leaves and roots, and increased POD activity in roots under both watering regimes; however, MDA concentration in the roots decreased. By contrast, AM fungi either had no effect or a slight negative effect on the shoot and root growth of female plants, with lower root biomass, total biomass and root/shoot ration under drought. In females, MDA concentration increased in leaves and roots under both watering regimes, and the proline content and POD activity of roots increased under drought conditions; however, POD activity significantly decreased under well-watered conditions. These findings suggest that AM fungi enhanced the tolerance of male plants to drought by improving shoot and root growth, biomass and the antioxidant system. Further investigation is needed to unravel the complex effects of AM fungi on the growth and antioxidant system of female plants.     

Aquatic hyphomycetes as endophytes of riparian plant roots

Eighteen species of aquatic hyphomycetes were recorded as root endophytes in roots of living plants including grasses and pteridophytes from wet fields near ravine areas. Alatospora acuminata, A. pulchella, Acaulopage tetraceros, Anguillospora crassa, Campylospora chaetocladia, Lemonniera cornuta, L. pseudofloscula, L. terrestris, Pestalotiopsis submersus and Tetrachaetum elegans were found for the first time as root endophytes. A. longissima, Campylospora purvula, Clavariopsis aquatica, Cylindrocarpon aquaticum, Heliscus lugdunensis, Lunulospora curvula, Tetracladium marchalianum and T. setigerum, which were known previously as root endophytes, are reported here on new hosts. Maximum occurrence was found in November and December.     

The influence of genotypic variation on metabolite diversity in populations of two endophytic fungal species

The relationship between metabolite production and genotypic diversity in two endophytic fungi was investigated. We selected populations of Cylindrocarpon destructans and Heliscus lugdunensis from the roots of a single tree. A total of 49 isolates of both species were selected and classified by simple genotypic tests (random amplified polymorphic DNA analysis and rDNA-ITS sequencing). In a blind test, the ability of these fungi to produce natural products was tested by ethyl acetate extraction of hyphae and culture filtrates, followed by high-performance liquid chromatography analysis (HPLC). A positive relationship was found between genotype classification and the pattern of natural products produced by a given isolate. To test the robustness of this correlation, a discriminate selection procedure was carried out by collecting fungal isolates from a second site and selecting a sub-set of the population, on the basis of genotypic variability. This sub-set of fungal isolates produced greater numbers of unique metabolites than those selected indiscriminately.     

Effects of Nutrient Enrichment on Decomposition and Fungal Colonization of Sweet Chestnut Leaves in an Iberian Stream (Central Portugal)

This study assessed the effect of nutrient enrichment on rates of decomposition, ergosterol concentrations (as a measure of fungal biomass), and rates of fungal sporulation of sweet chestnut (Castanea sativa Miller) leaves in a 3rd order stream (Central Portugal), with medium to high background values of nutrients. Coarse and fine mesh leaf bags were attached to nutrient diffusing substrata containing NaNO₃, KH₂PO₄, both nutrients, or no additions. Leaf breakdown rates were similar in the four treatments and in the two mesh sizes (k=−0.0155 to −0.0219 day⁻¹). Phosphorus content of P or N + P enriched leaves was higher than in the other treatments after 28 days, but there were no differences in N concentrations. Ergosterol concentrations associated with decomposing leaves were similar among treatments. The peak sporulation rates of aquatic hyphomycetes were stimulated by the addition of N + P and N but not by P alone. Results from the experiment provide evidence that leaf breakdown in the study stream, as a model for streams with naturally medium to high level of nutrients, was not nutrient-limited, and that fungal reproductive activity was limited by dissolved N but not by dissolved P in stream water.     

Effects of burial on leaf litter quality,microbial conditioning and palatability to three shredder taxa

Summary 1. Heterotrophic microorganisms are crucial for mineralising leaf litter and rendering it more palatable to leaf‐shredding invertebrates. A substantial part of leaf litter entering running waters may be buried in the streambed and thus be exposed to the constraining conditions prevailing in the hyporheic zone. The fate of this buried organic matter and particularly the role of microbial conditioning in this habitat remain largely unexplored. 2. The aim of this study was to determine how the location of leaf litter within the streambed (i.e. at the surface or buried), as well as the leaf litter burial history, may affect the leaf‐associated aquatic hyphomycete communities and therefore leaf consumption by invertebrate detritivores. We tested the hypotheses that (i) burial of leaf litter would result in lower decomposition rates associated with changes in microbial assemblages compared with leaf litter at the surface and (ii) altered microbial conditioning of buried leaf litter would lead to decreased quality and palatability to their consumers, translating into lower growth rates of detritivores. 3. These hypotheses were tested experimentally in a second‐order stream where leaf‐associated microbial communities, as well as leaf litter decomposition rates, elemental composition and toughness, were compared across controlled treatments differing by their location within the streambed. We examined the effects of the diverse conditioning treatments on decaying leaf palatability to consumers through feeding trials on three shredder taxa including a freshwater amphipod, of which we also determined the growth rate. 4. Microbial leaf litter decomposition, fungal biomass and sporulation rates were reduced when leaf litter was buried in the hyporheic zone. While the total species richness of fungal assemblages was similar among treatments, the composition of fungal assemblages was affected by leaf litter burial in sediment. 5. Leaf litter burial markedly affected the food quality (especially P content) of leaf material, probably due to the changes in microbial conditioning. Leaf litter palatability to shredders was highest for leaves exposed at the sediment surface and tended to be negatively related to leaf litter toughness and C/P ratio. In addition, burial of leaf litter led to lower amphipod growth rates, which were positively correlated with leaf litter P content. 6. These results emphasise the importance of leaf colonisation by aquatic fungi in the hyporheic zone of headwater streams, where fungal conditioning of leaf litter appears particularly critical for nutrient and energy transfer to higher trophic levels.     

Lower marine fungi (labyrinthulomycetes) and the decay of mangrove leaf litter

This paper deals with the association of members of the Labyrinthulomycetes (Thraustochytriales and Labyrinthulales) with decaying or decayed leaves at an intertidal mangrove at Morib, Malaysia. Representatives of both orders of these obligately marine unicellular eukaryotes of unresolved taxonomic affinities (Chamberlain & Moss, 1998) were consistently isolated from leaves at all stages of decay from the recently fallen to those in an advanced stage of decay, but not from either green or senescent yellow leaves attached to trees. Baiting experiments using -irradiated leaf discs of Sonneratia and Rhizophora spp. immersed in the aquatic environment of the mangrove, revealed that leaf material was colonised by both labyrinthulids and thraustochytrids within 24 hours of immersion at the test site and these organisms were isolated from the leaf material throughout the 14 day study period. In vitro experiments using axenic cultures of three thraustochytrid genera inoculated onto sterile discs of Sonneratia leaves and incubated for 14 days caused loss of both biomass and structural integrity of the leaf material. Freeze fracture, followed by scanning electron microscopy of leaves inoculated with a thraustochytrid and a strain of Labyrinthula, revealed that penetration of the leaf occured after 4 days and that the thraustochytrid was associated with localised degradation of internal leaf tissues. Cellulase production by an isolate of Schizochytrium aggregatum was detected. The results of all the above investigations are discussed with reference to the role of members of the Labyrinthulomycetes in nutrient cycling in the mangrove.     

Comparison of ATP and Ergosterol as Indicators of Fungal Biomass Associated with Decomposing Leaves in Streams

ATP and ergosterol were compared as indicators of fungal biomass associated with leaves decomposing in laboratory microcosms and streams. In all studies, the sporulation rates of the fungi colonizing leaves were also determined to compare patterns of fungal reproductive activity with patterns of mycelial growth. During leaf degradation, ATP concentrations exhibited significant, positive correlations with ergosterol concentrations in the laboratory and when leaves had been air dried prior to being submerged in a stream. However, when freshly shed leaves were submerged in a stream, concentrations of ATP and ergosterol were negatively correlated during degradation. This appeared to be due to the persistence of leaf-derived ATP in freshly shed leaves during the first 1 to 2 weeks in the stream. Estimates of fungal biomass from ergosterol concentrations of leaf litter were one to three times those calculated from ATP concentrations. ATP, ergosterol, and sporulation data generally provided similar information about the fungi associated with decomposing leaves in streams during periods when fungi were growing. Ergosterol concentrations provide a more accurate indication of fungal biomass in situations in which other organisms make significant contributions to ATP pools.     

单列毛壳菌通过促进秸秆降解并调控激素响应基因表达促进玉米生长

为探究生防真菌单列毛壳菌(Chaetomium uniseriatum)对秸秆降解和玉米(Zea mays)生长的影响,将单列毛壳菌接种到玉米盆栽土壤中,其它条件不变,以保证单一变量。于拔节期和抽雄期进行采样,通过测定土壤有机碳、土壤可溶性碳/氮、微生物量碳/氮以及酶活性,探究接种单列毛壳菌对土壤生物化学指标的影响。在抽雄期对秸秆降解率、地上部生物量、叶片SPAD值、玉米根系激素含量及根系转录组进行分析,探究接种单列毛壳菌对秸秆降解和玉米植株生长发育的影响。结果表明,接种单列毛壳菌后,土壤养分含量未出现显著性变化, β-葡萄糖苷酶(β-GC)活性显著降低;抽雄期玉米地上部生物量、叶片SPAD值以及秸秆降解率均显著高于对照组;玉米根系生长激素(IAA)和玉米素(ZR)含量均显著低于对照组。不同处理下玉米根系转录组分析筛选得到990个差异表达基因(383个基因表达上调,607个基因表达下调);对差异基因进行GO富集分析,得到5个植物激素相关的条目;KEGG富集分析得到1个与植物激素相关的通路(Pvalue<0.05,Q value<0.05)。综上,单列毛壳菌通过促进秸秆降解以...     

Laboratory conditions can change the complexity and composition of the natural aquatic mycobiome on Alnus glutinosa leaf litter

Community structure is of major interest when aquatic fungi are studied, particularly in leaf decomposition experiments. Although such studies are often conducted as laboratory experiments with microbial communities taken from the field, it remains unclear to what extent natural fungal communities can be sustained under experimental conditions. Here, we used DNA metabarcoding to investigate the development of fungal communities on alder leaves both under laboratory and field conditions. Five leaf conditioning treatments were compared by colonizing leaves in a stream, exposing stream colonized leaves to a defined medium or filtered stream water and using stream colonized leaves to inoculate sterile leaves in the defined medium or stream water. Fewer species were found on leaves that were inoculated under laboratory conditions, whereas differences in fungal community composition were comparably low in the other treatments, irrespective of the chosen medium. Possible shifts in fungal communities should therefore be considered in laboratory experiments.