How much ammunition did a german rifleman carry in world war 1?

British soldiers in WW1 wore 1908 pattern webbing instead of the usual leather belts used at the time, am invention by the American Mills Equipment Company. This webbing had 2 ammo pouches, each containing 75 rounds, so the answer to your question is 150.

Remember that the weapon on the front given to the common man was the Lee-Enfield Mk III, which a trained user could use to take 20-30 aimed shots a minute, so 150 rounds might not last long.