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Applied and Environmental Microbiology, March 2000, p. 1114-1119, Vol. 66, No. 3
Department of Biology, Mount Allison
University, Sackville, New Brunswick, Canada E4L
1G7,2 and Department of Biological
Sciences, Mangalore University, Mangalagangotri 574 199, Mangalore,
India1
Received 23 August 1999/Accepted 24 December 1999
Aquatic hyphomycetes dominate leaf decomposition in streams, and
their biomass is an important component in the diet of leaf-eating invertebrates. After 2 weeks of exposure in a first-order stream, maple
leaf disks had low levels of fungal biomass and species diversity.
Spore production by aquatic hyphomycetes also was low. Subsets of these
disks were left in the stream for another 3 weeks or incubated in
defined mineral solutions with one of three levels of nitrate and
phosphate. Stream disks lost mass, increased ergosterol levels and
spore production, and were colonized by additional fungal species.
External N and P significantly stimulated mass loss, ergosterol
accumulation, and spore production of laboratory disks. On disks
incubated without added N and P, ergosterol levels declined while
conidium production continued, suggesting conversion of existing hyphal
biomass to propagules. In all other treatments, approximately equal
amounts of newly synthesized biomass were invested in hyphae and
conidia. Net yield (fungal biomass per leaf mass lost) varied between
1% (in the laboratory, without added N or P) and 31% (decay in
stream). In most treatments, the three aquatic hyphomycete species that
dominated spore production during the first 2 weeks in the stream also
produced the largest numbers of conidia in the following 3 weeks.
Principal-component analysis suggested two divergent trends from the
initial fungal community established after 2 weeks in the stream. One
culminated in the community of the second phase of stream exposure, and
the other culminated in the laboratory treatment with the highest levels of N and P. The results suggest that fungal production in
streams, and, by extension, production of invertebrates and higher
tropic levels, is stimulated by inorganic N and P.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Initial Colonization, Nutrient Supply, and Fungal
Activity on Leaves Decaying in Streams
*
Corresponding author. Mailing address: 63B York St.,
Department of Biology, Mount Allison University, Sackville, New
Brunswick, Canada E4L 1G7. Phone: (506) 364 2513. Fax: (506) 364 2505. E-mail: fbaerlocher{at}mta.ca.
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