Fungi from High Nitrogen Environments—Ammonia Fungi: Eco-Physiological Aspects

Ammonia fungi are a chemoecological group of fungi in which reproductive structures appear after the addition of ammonia, urea, or other nitrogenous materials which react as bases, or of alkalis. The appearance of reproductive structures of ammonia fungi generally proceeds in the sequence: saprobic anamorphic fungi, saprobic fungi in Ascomycota, saprobic fungi in Basidiomycota having smaller fruit-bodies, and followed by mostly biotrophic and a few possibly saprobic fungi in Basidiomycota having larger fruit-bodies. The former three groups are described as early phase fungi (EP fungi) and the latter group described as late phase fungi (LP fungi). Spores germination of most ammonia fungi are stimulated by 10–300 mM NH4-N at pH 7–10. Early-stage EP fungi grow well at pH 7–9 and late-stage EP fungi at pH 6–8, whereas the LP fungi show optimum growth at pH 5–7. Ammonia fungi would be divided into three groups in terms of adaptation to ammonium-ion concentration, namely, high concentration of ammonium-ion adapted species, composed of some EP fungi, wide range concentrations of ammonium-ion adapted species, composed of some EP fungi, and high concentration of ammonium-ion non-adapted species, composed of some EP fungi and LP fungi. Reproductive structure formation of most 190ammonia fungi is accelerated through the vegetative growth stimulated of ammonium-nitrogen under weak alkaline to neutral conditions, although the fruiting of the late-stage EP fungi Coprinopsis spp. is directly induced by the presence of the ammonia or urea. Most early-stage EP fungi intermingle with each other whereas late-stage EP fungi inhibit the growth of early-stage EP fungi or invade into the territories of early-stage EP fungi, irrespective of pH conditions. LP fungus Hebeloma vinosophyllum invades into the territories of early-stage EP fungi under acidic condition, but not into those of late-stage EP at any pH conditions. In the five species cultures (early-stage EP fungi Amblyosporium botrytis and Ascobolus denudatus, late-stage EP fungi Tephrocybe tesquorum and Coprinopsis phlyctidospora, and LP fungus He. vinosophyllum), fruit-body formation of As. denudatus, T. tesquorum and C. phlyctidospora, and He. vinosophyllum are reduced, but not Am. botrytis. These suggest that successive occurrence of ammonia fungi is caused by the interactions among ammonia fungi as well as by the physiological characteristic of each fungus associates with conditions of its inhabiting soils such as pH and nitrogen concentration. Most ammonia fungi have clear cellulolytic and faint ligninolytic activities. The pH optima for the cellulolytic enzymes of EP fungi are between 6.8 and 9.0, and those for the cellulolytic enzymes of LP fungi are between 5.5 and 6.8. In ecosystems, ammonia fungi would have a role in keeping the carbon cycles instead of pre-inhabiting fungi after the addition of a large amount of nitrogenous materials, and ammonia fungi immobilize nitrogen derived from animal wastes such as urine, feces, and dead bodies. This replacement described may be view as a kind of 'compensation process' in nutrient cycle.