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Aquatic Microbial Ecology

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AME 32:95-103 (2003)  -  doi:10.3354/ame032095

Fungal content and activities in standing-decaying leaf blades of plants of the Georgia Coastal Ecosystems research area

Steven Y. Newell*

Marine Institute, University of Georgia, Sapelo Island, Georgia 31327, USA

ABSTRACT: Change in salinity, including expansion or contraction of salt- and freshwater marshes, due to altered river outflow may influence a variety of ecosystem processes, and the literature to date suggests that fungal activity in standing-decaying blades of macrophytes may be lower in freshwater marshes than in saltmarshes. I measured living-fungal mass (as ergosterol), rate of CO2 evolution, and rate of fungal membrane synthesis (acetate incorporation into ergosterol) for standing-decaying blades from a series of macrophytes, including saltmarsh cordgrass in both saline and fresher-water sites. Three terrestrial plants with prominent standing-decaying leaf blades were included for comparison. Species involved were: Spartina alterniflora, S. cynosuroides, Zizaniopsis miliacea, Typha angustifolia, Sabal palmetto, Uniola paniculata, and Panicum amarum. Although there was no difference in fungal content of S. alterniflora blades from saltier and fresher sites, there was a significant trend downwards (from >500 to <250 μg ergosterol g-1 system organic mass) in mean content of living-fungal mass moving from saltmarsh-adapted toward freshwater-adapted plants, and 2 of 3 terrestrial plants were also low (ca. 100 μg g-1). The activity measurements (CO2, acetate incorporation) revealed an opposite pattern: blades from fresher-water plants had higher activities per unit living-fungal mass (range of about 4-fold for mean rate of acetate incorporation per unit ergosterol), and lower CO2 release per unit fungal membrane synthesis, than did more saline-adapted plants. It is proposed that this is perhaps largely a consequence of the microstructure (lignification, cuticular hydrophobicity) of the blades of the fresher-water plants (and 2 of the terrestrial plants) limiting duration of fungal activity. Upon thorough wetting, such as eventually occurs when blades move to the marsh-sediment surface, fungi within the fresher-water blades would be permitted to grow quickly, which would explain reported increases in ergosterol content of fallen blades.

KEY WORDS: Fungal biomass · Fungal productivity · CO2 release · Standing decay · Ergosterol · Saltmarsh · Freshwater marsh · Altamaha River

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