TEMPERATURE AND SPORULATION OF AQUATIC HYPHOMYCETES

Temperature appears to be an important factor affecting the occurrence and distribution of aquatic hyphomycetes, the dominant leaf litter-de composing fungi in streams. We compared conidium production by eight s pecies of aquatic hyphomycetes grown on yellow poplar leaves in stream -simulating microcosms at three temperatures (15, 20, and 25 degrees). The greatest conidium production occurred at 15 degrees C for one spe cies, 20 degrees C for two species, and 25 degrees C for two species. Two species produced similar numbers of conidia at 20 and 25 degrees C , and one species produced similar numbers of conidia at all three tem peratures, Linear growth rates were determined on malt extract agar. S ix species had the same pattern of temperature responses for growth on malt extract agar as for sporulation on leaves, as shown by the posit ive correlations between the two parameters at the three temperatures. The species examined also exhibited differences in number of conidia produced from a similar amount of leaf material at a given temperature . These differences appeared to be due primarily to differences in ind ividual conidium mass (determined by weighing conidia produced from cu ltures), as shown by the relationship of the type Y = k/X (r(2) = 0.96 ), where Y is the number of conidia produced, X is the individual coni dium mass in milligrams, and k is a constant empirically determined to be 2.11. This finding supports the hypothesis that aquatic hyphomycet es allocate similar amounts of their resources to reproduction but var y with respect how these resources are partitioned into reproductive u nits (conidia).