Plot net ecosystem exchange (NEE) from Kangerlussuaq (2012 - 2014 growing seasons)

Net ecosystem CO2 exchange data were collected in the center of 1 m2 plots throughout the growing seasons of 2012 - 2014. A custom-built clear acrylic chamber (0.75 x 0.75 x 0.75 cm) was placed over the plot for 60-90 seconds. Air was circulated with two fans attached to the ceiling of the chamber. A pump moved air from the chamber to the infrared gas analyzer (LI-840, LI-COR Environmental, Lincoln, NE), where H2O and CO2 concentration was measured every second. Air temperature and PAR within the chamber were also logged every second. All data were stored on a LI-1400 datalogger (LI-COR Environmental). Clear chamber measurements represent net ecosystem CO2 exchange (NEE). Ecosystem respiration (ER) was measured by covering the chamber with an opaque cloth. Light-response curves were created by gradually darkening the chamber with three shade clothes of increasing density. Gross ecosystem photosynthesis (GEP) was calculated as: GEP = ER - NEE.