Ecological Archives E093-016-A1

Fernando Alfredo Lattanzi, German Darío Berone, Wolfgang Feneis, and Hans Schnyder. 2012. 13C-labeling shows the effect of hierarchy on the carbon gain of individuals and functional groups in dense field stands. Ecology 93:169–179.

Appendix A. A scheme of the labeling facility.

Fig. A1. MFC: digital adjustable mass flow controller, FM: optical flow meter, NV: needle valve, IRGA: infrared gas analyzer for monitoring of pCO2 inside the labeling chamber. Arrows indicate flow of atmospheric air (green), CO2-/H2O-free air (blue), pure CO2 (red), and mixed, labeling air (black).

The labeling apparatus produced CO2-free air (air generating unit), mixed it with pure CO2 of known isotopic composition (air mixing unit), and distributed it to transparent chambers enclosing the stands to be labeled (air distribution unit). The elements of the air generating unit were two: a compressor and an adsorption dryer. The compressor generated a flow of air at constant pressure (8 atm), and the dryer contained a molecular sieve (Silicagel WS plus Aluminiumgel F200) that trapped CO2 and H2O vapor (residual pCO2 < 5 µbar).

The dryer comprised two columns, each with 79 kg of molecular sieve. While one column was in operation at 7 atm, one-third of the CO2-/H2O-free air produced was diverted to pass through the second column (at 1 atm), to vent desorbed CO2 and H2O. A valve switched the air flow between columns every 5 min. The pressure and overflow requirements of this cold self-regeneration system reduced usable air flow to about 45% of the compressor technical specification, i.e., from 4000 L min-1 (at 8 atm) to 1800 L/min.

Air was filtered before (EC 48 and EE 48, Kaeser; G14XPD, Zander) and after the dryer (G14VHD, Zander). Thus cleaned from oil and dust, CO2-/H2O-free air was routed to a buffer tank (500 L), and then to an additional set of filters (FFG 48, Kaeser). Air flow rate and CO2 partial pressure (pCO2) were manually controlled via two digital mass flow controllers (Fig. 1), one for CO2-/H2O-free air (range: 150 to 3000 L/min) and one for pure CO2 (range: 0.005 to 1.0 L/min). Pure 13C-enriched CO2 was kept in an aluminum cylinder fitted with a pressure regulator and Teflon tubing. Mixing of the labeling CO2 and the CO2-/H2O-free air occurred in a simple ‘T’ connector.

Air was partitioned between groups of labeling chambers in an air distribution unit consisting of a set of connectors that routed air flow to four optical volumetric flow meters, each fitted with a needle valve. Chambers located at different distances from the air mixing unit experienced different pressure drops (depending on tubing length), which caused differences in flow. These differences were detected by the flow meters and neutralized by manual adjustment of the needle valves.

The total cost of the facility (except 13CO2) was ~ € 50,000.- (at 2007 prices).

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