Abstract
Each fungus species utilizes various nitrogenous materials for its growth. A large input of urea in the field would always happen sporadically in the field by the urine of mammalians. The urea in the urine would be decomposed mainly by bacteria and then utilized as inorganic nitrogen by many microbes including fungi. Thus, we examined the urease activities of 30 species (82 isolates) of fungi by modified Christensen media. Most of saprobic ammonia fungi such as Amblyosporium botrytis and Ascobolus denudatus and a few non-ammonia fungi such as Am. spongiosum, As. carbonarius, and Microporus vernicipes showed strong urease activities. Most saprobic non-ammonia fungi such as Pleurotus eryngii and Flammulina velutipes did not show urease activities and were killed by urea and/or phenol red added as pH indicator. A few ectomycorhizal ammonia fungi such as Hebeloma vinosophyllum and Alnicola lactariolens showed strong urease activities but ectomycorrhizal non-ammonia fungi such as Lyophyllum shimeji did not show any urease activity. Among tested isolates showing no urease activities, several saprobic non-ammonia fungi such as Trichophaea abundans and Pholiota highlandensis grew on the media. It means that these fungi utilized urea directly as a nitrogen source without its decomposition. The results suggest that most of saprobic ammonia fungi have the ability to colonize just after input of urea in the field whereas ectomycorrhizal ammonia fungi would survive the high stress by urea and/or ammonia derived from urea but have no ability to colonize within short days after urea input.
