276 F. L. Bunnell et al. 



during the growing season, and never does attain the levels measured in 

 other habitats. 



In wet meadows, seasonal mean estimates of fungal densities in litter 

 (x ±SE) were 2442 ±654 m mycelia (gdw litter)"' in 1972, and 2127 ±664 

 m mycelia (gdw litter)"' in 1973. The microclimatic regime of the litter 

 layer is typically moister than that for standing dead and the increased 

 precipitation of 1973 apparently was insufficient to alter measures of 

 average litter biomass. 



Fungi in the Soil 



The seasonal patterns of fungal biomass in the surface layer of soil 

 (1 to 2 cm) show a peak immediately after snowmelt followed by a se- 

 cond peak in early August, which may be as pronounced as the first, 

 moderate, or weak (Figure 8-7) (Laursen 1975). The magnitude of the 

 first peak for troughs and basins may be underestimated because the soils 

 were frozen at the time of the first sample and the highest levels may have 

 been reached before the next measurement. More pronounced early 

 peaks in fungal biomass were observed in the surface soil of polygon 

 troughs in 1972 and 1974 (Laursen and Miller 1977). Except for the se- 

 cond, variably expressed increase, a general decline in biomass similar to 

 that observed among litter fungi is evident over the season (Figures 8-6 

 and 8-7). The pattern of a moderate peak followed by a gradual decline 

 that was observed in the wet meadow is also evident in data from 

 Norwegian sites (Hanssen and Goks(^yr 1975). The rapid early growth of 

 fungal biomass in the surface layer of soil, as well as in the litter, may be 

 a response to the release of nutrients during snowmelt. The second peak 

 occurs just before the basidiomycetes fruit and is often more pronounced 

 in the more productive microtopographic units (Figure 8-7). The same 

 factors that restrict biomass of soil fungi in the polygon troughs and 

 basins of low-centered polygons may also restrict the ability of these 

 fungi to respond quickly to favorable conditions. Thus the seasonal 

 courses of fungal biomass are not only lower, but less variable in troughs 

 and basins than in the other microtopographic units. 



Seasonal patterns at a depth of 6 to 7 cm do not mimic patterns at 1 

 to 2 cm depth (Figure 8-7). The only apparent consistency in the seasonal 

 pattern among microtopographic units in the deeper soil is the peak in 

 fungal biomass that occurs in all units around 22 August. The decline in 

 fungal biomass in the surface soil that begins in late August is probably 

 associated with freezing or near-freezing temperatures in that stratum. 

 Fungal biomass in the deeper soil typically equals or exceeds the biomass 

 in the surface soil by mid-September (Laursen and Miller 1977). 



The taxonomic structure of both soil and litter fungi appears to shift 



