Pectinases in leaf degradation by aquatic hyphomycetes I: the field study : The colonization-pattern of aquatic Hyphomycetes on leaf packs in a surrey stream.

The colonization-pattern of aquatic Hyphomycetes on five-gram leaf packs of oak and alder submerged in a stream was quantified and compared. There were three series of alder leaves, submerged two weeks apart, and one series of oak. Colonization of leaves by pectolytic bacteria was also measured. There were marked similarities in the colonization of all four series. Total spore counts/g dry wt of leaf rose to a peak followed by a decline. The time taken to peak colonization was slower in oak than in alder, and in alder depended on the level of inoculum in the stream, as did the extent of colonization. Pectolytic bacteria counts followed the pattern of total spore counts, suggesting the exploitation of the same substrates by bacteria and fungi. Temperature and micro-environmental factors influence the overall rate of leaf degradation. Alder I was skeletonized in 10 wks, Alders II and III in 12 wks and oak in 25 wks.The resource was shown to have an upper limit of microbial colonization, and within this 'unit-community' of microbes, there was an association of four dominant species of aquatic Hyphomycetes, together with about ten occasional species. The dominant species are subject to selection from the inoculum available in the stream and the formation and maintenance of the association appears to be the result of competitive interactions between species which results in a dynamic equilibrium. There is a low degree of resource specificity. The species equilibrium is 14 for all series, and species numbers are initially low, rise to a peak, then tend to decline. There is a taxonomic similarity of about 60% between successive stands of all series and between matched stands of alder.