James P. Amon

TEMPERATE ZONE FENS OF THE GLACIATED MIDWESTERN USA

A study of more than 70 fens in the Midwestern United States and a review of the literature indicates that these temperate zone wetlands may differ from fens of the boreal zone and are not adequately differentiated from the by present classification systems. Fens of the Midwestern temperate zone 1) are wetlands with high botanical diversity, 2) are supported in part by ground water with conductivity > 100mS/cm and circumneutral pH, 3) contain water in the root zone during most of the growing season yet are not usually innndated, and 4) accumulate organic and/or carbonate substrates. Individually, none of these descriptors is adequate to distinguish fens from other wetland communities of the Midwest such as marshes, sedge meadows, and wet prairies; yet, when they are taken together, such discrimination is possible. While fens of this zone share many species, our study does not support using indicator species because too few are both faithfully represented and geographically widespread. Midwestern temperate fens are sustained by forces of climate, landscape, and geology, which permit ground water to seep continuously into the root zone in a focused location. Since water availability in the temperate Midwest is less than in the boreal zone, continuous discharge is needed to maintain the saturation conducive to peat formation.

Seasonal dynamics of arbuscular mycorrhizal fungi in differing wetland habitats

The dynamics and role of arbuscular mycorrhizal fungi (AMF) have been well described in terrestrial ecosystems; however, little is known about how the dynamics of AMF are related to the ecology of wetland ecosystems. The seasonal dynamics of arbuscular mycorrhizal (AM) colonization within different wetland habitats were examined in this study to determine the factors that influence AM associations and to further assess the ecological role of AMF in wetlands. Fen and marsh habitats of four wetlands in west central Ohio were sampled monthly from March to September. AMF were found at all four sites for each month sampled and were present in all of the dominant plant species. A significant effect of month (P<0.001) on AM colonization did occur and was attributable to maximum colonization levels in the spring and minimum levels in late summer. This trend existed in all four wetlands in both fen and marsh habitats, regardless of variation in water levels, percent soil moisture, or available phosphorus levels. Because abiotic factors had minimal influence on AM colonization variation and the level of AM colonization paralleled plant growth patterns, we conclude that the AM seasonal dynamic was in response to plant phenology. Our data suggest that AM associations in temperate fen and marsh habitats are prevalent in the spring during new root and vegetative growth, even for plants experiencing flooded conditions. Evidence of an overriding AM seasonal trend indicates that future studies should include a seasonal component to better assess the role and distribution of AMF in wetland ecosystems.

Mycorrhizal fungi associated with plants in ground-water fed wetlands

Studies have documented the flora, fauna, and soils of ground-water fed wetlands, but very little is known about their plant-mycorrhizal associations. This study was designed to determine the presence of arbuscular mycorrhizal (AM) fungi in several wetland plant species associated with fens in west central Ohio, USA. Roots of wetland plant species collected at four sites had mycorrhizal fungal colonization levels ranging from O to 61.5%. Mycorrhizal associations occurred in plants of all wetland categories (OBL, FACW, FAC). We propose that these peatland have lower nutrient availability than some other wetlands and thus may be more dependent on these root fungi for nutrient uptake. Mycorrhizal fungi may be an important consideration in the functional restoration of ground-water driven wetland systems.

Zoosporic true fungi in marine ecosystems: a review

Although many species of zoosporic true fungi have been frequently observed and studied in freshwater and soil ecosystems, only three species have been properly identified and partially characterised from brackish and marine ecosystems, namely Rhizophydium littoreum Amon, Thalassochytrium gracilariopsis Nyvall, Pedersen et Longcore and Chytridium polysiphoniae Cohn. These species are either facultative or obligate parasites of marine macroalgae and invertebrates. Also, some species of Olpidium and Rhizophydium are parasites of small marine green algae and diatoms. Although the physiological effects of these pathogens on the growth and metabolism of their hosts are poorly understood, parasitism by C. polysiphoniae possibly affects the rates of photosynthesis and patterns of growth in infected communities of brown algae. Saprobic ecotypes of R. littoreum can also colonise dead-plant and animal substrates. Zoospores from zoosporic true fungi and other groups of microbes possibly provide important food resources for grazing and filter-feeding zooplankton and metazoans in marine ecosystems where the prevalence of disease is high or where accumulated detritus enhances biodiversity in food webs. However, quantitative studies have not yet been attempted. Recently, environmental sampling with molecular techniques has revealed unknown clades of zoosporic true fungi in extreme marine ecosystems. These fungi have been grossly under-sampled and under-studied in marine environments.

Thraustochytrids and Labyrinthulids of Terrestrial, Aquatic and Hypersaline Environments of the Great Salt Lake, USA

(1978). Thraustochytrids and Labyrinthulids of Terrestrial, Aquatic and Hypersaline Environments of the Great Salt Lake, USA. Mycologia: Vol. 70, No. 6, pp. 1299-1301.

RHIZOPHYDIUM LITTOREUM: A CHYTRID FROM SIPHONACEOUS MARINE ALGAE-AN ULTRASTRUCTURAL EXAMINATION

The obligately marine phototactic chytrid described by Kazama and the chytrid Phlyctochytrium aestuarii Ulken are both placed in the genus Rhizophydium. A comparison shows that Kazamas isolate, the chytrid described by Porter and Smiley, and a new isolate from Codium are probably of the same species.

An Estuarine Species of Phlyctochytrium (Chytridiales) Having A Transient Requirement for Sodium

Microorganisms found exclusively in marine environments appear to exist there because that environment can provide them with the necessary chemical, physical, or biological conditions (10, 12, 22). In studies with some marine bacteria MacLeod (12) found that sodium is required at concentrations approaching that of seawater. Vishniac (22) reported that many lower fungi found in the marine environment also require sodium. Fungi such as Pythilm ml arinnllnl Sparrow (10), Phlyctochytriitt. niangrovii Ulken (21), Dendryphiella salina (Sunderl.) Nico & Pugh (2, 3), and Litzcorthia sp. (5) require either sodium or somle other factor characteristic of the marine environment

Photoresponses of the marine protist Ulkenia sp. zoospores to ambient, artificial and bioluminescent light

Ulkenia sp. zoospores are attracted to 492 nm wavelength light produced by the marine bacterium Vibrio fischeri. Zoospores are positively photoresponsive to wavelengths of 440, 460 and 480 nm and contain a pigment that absorbs blue light. The average velocity of the zoospores is 0.47 m h−1. Stimulatory intensities of these wavelengths ranged from 0.5 to 3.5 μEm−2 s−1 in both laboratory and field studies. The response of this protist to bioluminescence produced by Vibrio fischeri may direct zoospores to a nutrient rich environment colonized by these bacteria. In addition, the greatest responses were found at intensities associated with the light regime found near the bottom of naturally turbid estuaries or at greater depths of nonturbid, offshore waters. Positive phototaxis was not seen in zones of high light intensity either in field or laboratory studies, and there is some indication that zoospores may swim away from high light intensities.

THE EFFECT OF SALINITY ON THE GROWTH OF TWO MARINE FUNGI IN MIXED CULTURE

Phlyctochytrium sp. and Thraustochytrium striatum, isolated from estuarine environments, are described growing in two-member and in single species cultures. Pinus taeda pollen is used to support growth at various salinities ranging from nearly freshwater to hypersaline water. Both species grow poorly or not at all at the lowest salinities. Phlyctochytrium sp. appears to grow better at low to intermediate salinities than T. striatum which grows better in intermediate to hypersaline conditions. In two-member cultures, growth of T. striatum is depressed below the expected rate at low salinities; conversely, growth of Phlyctochytrium sp. is slower than expected at high salinities. When T. striatum is initially numerically dominant, Phlyctochytrium still becomes the dominant species over time in low to intermediate salinities. The result implies the probable distribution by salinity in the natural environment.

Nutritional Studies of a Marine Phlyctochytrium Sp.

An estuarine chytrid, Phlyctochytrium sp., requires higher concentrations of Na+, Mg2+ and Ca2+ than the concentrations in freshwater but lower than those found in ocean water. Good growth is obtained in low concentrations of K+, but high concentrations are not harmful. A pH optimum of 5-8 is attributed to the broad range of pH possible in estuaries. Glucose, starch, maltose, and glutamic acid can serve as sole carbon sources, and NH4C1, but not KNO3, serves as a sole nitrogen source. The organism grows well in the defined medium used. The medium, varied within the limits shown, is suggested as a basal medium for further studies.