I don't know the exact specs here, but putting a turbo on a 1.8 car means it requires more air, depending on the size of the turbo it can need more air than a 3.2 litre engine!
Both systems suck air in, NA and Turbo, it is only after the turbo has spooled up that it forces air into the cylinders, but it is still sucking air in from the MAF.