A LABELING CHAMBER FOR C-13 ENRICHMENT OF PLANT-TISSUE FOR DECOMPOSITION STUDIES

Isotope labeling with a (CO2)-C-13-enriched atmosphere was conducted on four raised beds of grain sorghum. A temporary rain shelter with clear polyethylene roofing material was constructed to allow controlled watering of the beds. Labeling chambers were constructed with aluminum frames, polyethylene sides and propofilm C tops. The chamber length (4 m) was one-quarter of the total bed length and enclosed a total volume of approximately 3000 l. A fan recirculated air in the chamber through polyvinyl chloride pipes. An outlet allowed sampling of chamber atmosphere for CO2 concentration, while another opening downstream provided an inlet for (CO2)-C-13 injection. An elevated extension was added when the grain sorphum grew to exceed the 50-cm height of the chamber, doubling the enclosed volume. Enrichment of the chamber atmosphere with (CO2)-C-13 was monitored with infrared gas analyzers. Gas flowmeters were used to measure isotope additions.