THE EFFECT OF TEMPERATURE AND SUBSTRATUM ON COMPETITION AMONG 3 SPECIES OF FOREST LITTER MICROFUNGI

The influence of temperature, substratum type and presence of other fungi on the ability of two low temperature (LT) fungi (Geomyces pannorus and Mortierella hyalina) and one mesophile (Trichoderma longibrachiatum) to germinate, grow and reproduce in an in vitro system was examined. To determine how physical and biotic factors interact to affect niche differentiation among these fungi, spores of each species were placed either singly or in species pairs on oak leaf discs or moth wings and incubated at 0-degrees-C, 10-degrees and 20-degrees. When incubated singly, the two LT species grew on both substrata at all three temperatures. However, the presence of T. longibrachiatum reduced sporulation of G. pannorus and M. hyalina on oak leaves and moth wings at 20-degrees. At 10-degrees T. longibrachiatum proved to be a more effective competitor on oak leaves, while M. hyalina was the best competitor on moth wings. At 0-degrees T. longibrachiatum did not grow on either substratum. Mortierella hyalina was highly competitive against G. pannorus on moth wings at 0-degrees, while G. pannorus was a better competitor than M. hyalina on oak leaves. These results suggest that these soil and litter fungi can occupy separate temporal and spatial niches that are temperature and substrate controlled. During colder seasons when competition from mesophiles such as T. longibrachiatum may be limited, G. pannorus and M. hyalina may be active in the forest floor on plant and invertebrate remains, respectively. Although these LT species are potentially able to colonize these substrata at 20-degrees, their activity may be restricted by interactions with mesophilic fungi in warmer months. However, the relatively high competitive ability of M. hyalina on moth wings even at 20-degrees implies that it could retain a niche on invertebrate remains in litter and upper soil horizons during warmer seasons. The activity of LT fungi throughout much of the year in the forest floor of temperature forests, as well as their roles in deep soil decompositional processes, may be more important than previously recognized.