北京地区水泡中的丝孢菌及其生态

本文报道北京及其邻近地区4个水域泡沫中的水生丝孢菌14属21种,其中6属11种为中国新记录,它们是:粗水线孢Anguillospora crassa Ingold,膨顶节枝孢Articulospora inflata Ingold,四节枝孢A.tetracladia Ingold,立水枝孢Dendrospora erecta Ingold,梯状小双枝孢Diplocladiella scalaroides Arnaud,星状小钉孢Heliscella stellata(Ing.&Cox)Nilsson ex Marvanova&Nilsson,奴地疣钉孢Heliscus lugdunensis Saccardo&Therry,阿地放射孢Lemonniera alabamensis Sinclair＆Morgan,细丽三枝孢Tricladium gracile Ingold,明丽三枝孢T.splendens Ingold,和多枝变孢霉Varicosporium elodeae Kegel。同时讨论了这类真菌与其生态环境之间的相关性及其分布。     

Diversity and activity of aquatic fungi under low oxygen conditions

1. The objective was to test whether a decrease in oxygen concentration in streams affects the diversity and activity of aquatic hyphomycetes and consequently leaf litter decomposition. 2. Senescent leaves of Alnus glutinosa were immersed for 7 days in a reference stream, for fungal colonization, and then incubated for 18 days in microcosms at five oxygen concentrations (4%, 26%, 54%, 76% and 94% saturation). Leaf decomposition (as loss of leaf toughness), fungal diversity, reproduction (as spore production) and biomass (ergosterol content) were determined. 3. Leaf toughness decreased by 70% in leaves exposed to the highest O₂ concentration, whereas the decrease was substantially less (from 25% to 45%) in treatments with lower O₂. Fungal biomass decreased from 99 to 12 mg fungi g⁻¹ ash‐free dry mass on exposure to 94% and 4% O₂ respectively. Sporulation was strongly inhibited by reduction of dissolved O₂ in water (3.1 × 10⁴ versus 1.3 × 10³ spores per microcosms) for 94% and 4% saturation respectively. 4. A total of 20 species of aquatic hyphomycetes were identified on leaves exposed to 94% O₂, whereas only 12 species were found in the treatment with 4% O₂ saturation. Multidimensional scaling revealed that fungal assemblages exposed to 4% O₂ were separated from all the others. Articulospora tetracladia, Cylindrocarpon sp. and Flagellospora curta were the dominant species in microcosms with 4% O₂, while Flagellospora curvula and Anguillospora filiformis were dominant at higher O₂ concentrations. 5. Overall results suggest that the functional role of aquatic hyphomycetes as decomposers of leaf litter is limited when the concentration of dissolved oxygen in streams is low.     

中国西藏土壤中节格孢属真菌的三个新种

从中国西藏土壤中分离到3种节格孢属Scytalidium真菌,据形态学特征和分子系统学分析,他们不属于该属中任何已知种,遂在本文中作为新种加以描述和发表,它们是：具有多纵隔膜的中国节格孢S. chinense、能产红色色素的西藏节格孢S. tibetense和孢子与菌丝均具瘤突的具瘤节格孢S. tuberculatum。新种的模式标本（干制培养物）分别保藏在山东农业大学植物病理学标本室（HSAUP）和中国科学院菌物标本馆（HMAS）。     

Allelopathic inhibition of primary producer growth and photosynthesis by aquatic fungi

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

葡萄穗霉属四新种暨中国土壤中该属真菌已知种检索表(英文)

从中国不同地区的土壤中分离获得葡萄穗霉属Stachybotrys 4个新种:阿克苏葡萄穗霉S.aksuensis、两形葡萄穗霉S.biformis、海滨葡萄穗霉S.littoralis和玉树葡萄穗霉S.yushuensis。对新种与各自相似种的区别进行了讨论。文中为中国土壤中已知的24种葡萄穗霉菌提供了检索表。新种模式标本(干制培养物)与活菌种保藏于山东农业大学植物病理学标本室(HSAUP),等模式标本(干制培养物)存放在中国科学院菌物标本馆(HMAS)。     

Microscopy- or DNA-based analyses: Which methodology gives a truer picture of stream-dwelling decomposer fungal diversity?

We assessed aquatic hyphomycete diversity in autumn and spring on oak leaves decomposing in five streams along a gradient of eutrophication in the Northwest of Portugal. Diversity was assessed through microscopy-based (identification by spore morphology) and DNA-based techniques (Denaturing Gradient Gel Electrophoresis and 454 pyrosequencing). Pyrosequencing revealed five times greater diversity than DGGE. About 21% of all aquatic hyphomycete species were exclusively detected by pyrosequencing and 26% exclusively by spore identification. In some streams, more than half of the recorded species would have remained undetected if we had relied only on spore identification. Nevertheless, in spring aquatic hyphomycete diversity was higher based on spore identification, probably because many species occurring in this season are not yet connected to ITS barcodes in genetic databases. Pyrosequencing was a powerful tool for revealing aquatic hyphomycete diversity on decomposing plant litter in streams and we strongly encourage researchers to continue the effort in barcoding fungal species.     

Raised water temperature lowers diversity of hyporheic aquatic hyphomycetes

1. The hyporheic zone of a permanent first‐order stream was divided into a treatment and a control section using a 1 m deep sheet‐metal barrier. During a 4‐month pre‐treatment period, water temperatures in two transects of the two sections were not different. Upon heating, the water temperature in the treatment transect increased by an average of 4.3 °C over values in the control transect. 2. Eleven bimonthly core samples were taken from a treatment and a control transect, and recovered CPOM was classified as twigs, wood, grass, roots, cedar and deciduous leaves. 3. In both transects, twigs were the most common and deciduous leaves the least common substrates. The number of leaf fragments declined significantly in the heat‐treated transect. 4. Diversity and frequencies of occurrence of aquatic hyphomycetes were highest on leaves and lowest on grass and wood. On leaves, their frequency of occurrence was higher in control than in treatment samples. 5. Preliminary results with amplified and cloned 18S DNA sequences revealed many fungal taxa with high affinities to Basidiomycota, particularly to Limnoperdon incarnatum. 6. By itself, higher water temperature due to global warming is likely to lower the availability of substrates for, and therefore the occurrence of, aquatic hyphomycetes.     

Intraspecific diversity affects stress response and the ecological performance of a cosmopolitan aquatic fungus

Fungi play an important role in organic matter turnover and ensure key ecosystem services in freshwaters. The relationships between intraspecific fungal diversity and key ecological processes remain largely unknown. We examined the effects of intraspecific diversity of Articulospora tetracladia, a cosmopolitan fungal decomposer thriving on plant detritus in streams. Alder leaves were inoculated with 1 or mixtures of 2–8 fungal strains for 35 d, and leaf litter decomposition and fungal reproduction were quantified in the presence and absence of 2 mg L⁻¹ of cadmium (Cd), a common stressor in polluted streams. Intraspecific diversity and identity affected fungal reproduction, but not leaf decomposition. Under metal stress, leaf decomposition slightly increased with intraspecific diversity. Fungal reproduction increased with intraspecific diversity and was greater in mixed assemblages, either in the absence or presence of Cd. Effect size of intraspecific diversity was higher under Cd stress for fungal reproduction, but no differences were found for leaf mass loss, with or without metal. The impacts of intraspecific diversity loss may jeopardize fungal survival and fungal functions, namely microbial leaf decomposition and leaf litter condition for invertebrate shredders in streams, particularly under metal stress.     

Does the growth rate hypothesis apply to aquatic hyphomycetes?

The growth rate hypothesis states that in many organisms or tissues, the specific growth rate μ correlates with RNA concentrations. Since RNA often accounts for much of the phosphorus content of cells, μ may also correlate positively with P concentrations and negatively with C:P and N:P ratios. We tested this hypothesis with broth cultures of five aquatic hyphomycete species. Samples were harvested on eight occasions after 3–56 d of incubation. Accumulation of biomass was fitted to a rectangular hyperbola, whose parameters were used to estimate μ. There were no consistent trends related to culture age or μ for C, N, P or ergosterol concentrations. RNA and DNA concentrations and RNA:DNA ratios were significantly and negatively correlated with culture age. Only RNA concentrations were positively and linearly correlated with μ. While RNA or DNA concentrations are unsuitable as indicators for total biomass, levels of fungal RNA combined with markers for fungal biomass may allow estimates of the extent to which the mycelia are metabolically active.     

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.