Ammonium transporter that mediates the import of ammonium in prespore cells. Controls ammonium homeostasis during growth and development. Ammonium has been shown to function as a morphogen at multiple steps during the development. May function as an ammonia sensor that relays information concerning ammonia concentrations to the signaling pathway involved in the slug versus culmination choice and regulates prestalk gene expression. Predominantly found in the prespores of the slug. Belongs to the ammonia transporter channel (TC 1.A.11.2) family.