A combustor for a gas turbine engine comprises an inner annular liner and an outer annular liner. A first and a second combustion stages are defined between the liners, each said combustion stage having a plurality of fuel injection bores distributed in a liner wall defining the respective stage. Valves at the fuel injection bores of one of the combustion stages, the valves each defining an air passage from an exterior to an interior of the combustion stage, the valves each having an actuatable member for adjusting a size of a respective air passage for air staging the combustor.