Flow through a multiplexing gas-exchange system for measuring CO2 flux at the moss surface of a boreal forest.  The system sequentially measured the exchange in 10 closed-type chambers, completing a circuit every 3 hours. Air was circulated between the selected chamber and the CO2 gas analyzer (IRGA) and mass flow controller (mfc) at 5 slpm following the arrows. The system was shipped and operated in three weather-tight boxes which sat on the forest  floor within 15 m of the chambers (Goulden and Crill 1997).