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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 ofAMF in wetland ecosystems.

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, Pedersén 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.

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