2. Technology of CO₂ enrichment

Twenty plots (each 1.1 m²) are exposed to elevated CO₂ (target value of 550 ppm) using a FACE system with pure CO₂ release. Another 20 plots are used as controls at a current ambient CO₂ concentration (370 ppm).

Liquid CO₂ is brought in by helicopter biweekly. CO₂ is then delivered to a control system in the field equipped with an infrared gas analyzer (IRGA) for CO₂ measurement, a control PC and an array of solenoid valves for CO₂ flow control (see Fig. 2). Four enriched plots are supplied with CO₂ according to actual CO₂ concentrations measured within a reference plot.

The pure CO₂ release technology proved suitable for CO₂ enrichment of natural vegetation at our remote treeline site. Reliable CO₂ control was achieved comparable to previous FACE systems with relatively small fluctuations around the target CO₂ concentration (see Fig. 4).

Seasonal averages of CO₂ concentrations (2001-2003; ± SD) were 566 ± 42, 582 ± 35 and 579 ± 52 ppm (data analysis courtesy of G. Grun).