Elongated chambers for field studies across atmospheric CO2 gradients

We describe a field facility that controls CO2 along continuous gradients from superambient to subambient concentrations. The facility consists of two transparent, tunnel-shaped chambers, each 1-m wide and tall and 60-m long. Pure CO2 is injected into one chamber during daylight to initiate a superambient CO2 gradient (550–350 µmol mol–1). Ambient air is introduced to the second chamber to initiate a subambient CO2 gradient (350–200 µmol mol–1). CO2 concentrations at night are regulated at 150 µmol mol–1 above daytime values along each gradient. The CO2 gradients are maintained by varying the rate and direction (day/night) of air flow