Li 8150 system

Soil CO₂ concentration measurements were made during the growing season of 2009 using Vaisala CARBOCAP solid‐state CO₂ sensors (model GMT 221, Vaisala, Helsinki, Finland) at depths of 10 and 5 cm and the Li‐8150 system (Li‐Cor, Lincoln, NE, USA) at 0 cm. At the same depths, soil temperature (averaging soil thermocouple probe TCAV; Campbell Scientific) and moisture (ML2x; Delta‐T Devices, Cambridge, UK) were measured, and incident photosynthetically active radiation (PAR) (BF2H; Delta‐T Devices) was measured above the canopy at 2 m height. Continuous recordings at 0.05 Hz were averaged and half‐hourly values recorded using an automated station (CR10X; Campbell Scientific). Values of soil CO₂ concentration were corrected for temperature and pressure using the ideal gas law according to the manufacturer (Vaisala, Helsinki, Finland). Soil CO₂ efflux at the soil surface was measured using an automated soil respiration system (Li‐8100 and Li‐8150; Li‐Cor, Lincoln, NE, USA) over measurement intervals of 2 min. The chambers were white to minimize heating. Possible pressure changes due to a Venturi effect are largely eliminated by the design of the vent used with the chamber [Xu et al., 2006].