Seasonality of Trichoderma Species in a Spruce-Forest Soil

SUMMARY

An intensive study of the occurrence of Trichodcrma species in a spruce-forest soil was conducted to investigate the effects of seasonal change on Trichodcrma populations. Nine species of Trichoderma were isolated, of which two are undescribed species. Of the species which occurred at relatively high frequencies, T. polysporum was most abundant in the fall and winter, T. viride in the spring and fall and T. koningii and an undescribed species (LP 58) were most abundant in the summer mo. All species showed a high level of spatial variation at all times of the year. A multiple-regression analysis, relating the occurrence of the Trichodcrma species to measured environmental parameters, indicated that, for T. viride, there was a significant relationship between its occurrence and soil moisture content and temperature. For the other three common species, the best predictive equations incorporated biotic variables, mainly the occurrence of other Trichoderma species. It is therefore suggested that the seasonal variation in the occurrence of Trichodermas is mediated to a large extent by competition with other species rather than by the direct effect of abiotic factors.