Ammonium transporter that mediates the excretion of ammonium. Controls ammonium homeostasis during growth and development. Ammonium has been shown to function as a morphogen at multiple steps during the development. Predominantly found in the prestalk of the slug. Shortens transitional period (when fingers and migrating slugs assess their environment to determine the appropriateness of that environment for culmination and fruiting body formation) of 1 to 2 hours and rarely forms slugs under standard conditions of development. Gives a slightly enhanced growth rate in axenic cultures. Belongs to the ammonia transporter channel (TC 1.A.11.2) family.