FIG. 1.

C₂H₂ reduction by organisms beneath shards from the gypsum rock, sampled in March 2003. Shards from the gypsum rock with a distinct bluish-green layer beneath were transferred to 1-liter flasks, covered with Suba-Seal septa, and supplemented with 10 ml of C₂H₂ at the field site (zero point on the abscissa of the graph). Two flasks were kept in continuous daylight (▴), whereas the other two (□) were assayed in the dark (wrapped with aluminum foil). Standard deviations (error bars) refer to different C₂H₄ determinations in the gas chromatograph (n = 2). Each point in this graph (and in Fig. 2 and 3) reflects the sum of the gas produced from the beginning till the determination.