FIG. 2.

C₂H₂ reduction by organisms beneath shards from the gypsum rock after a prolonged period of drought. Shards were sampled in June 2003, after a period of drought lasting at least 6 weeks. The experimental conditions were the same as those for Fig. 1. Since no activity was obtained during the first 7 days, moisture was added to the flasks (arrow). After the 7th day, conditions in the flasks were as follows: 2% O₂, natural light-dark cycle, moisture added (solid triangles with dashed lines); air, natural light-dark cycle, moisture added (solid triangles with solid lines); 2% O₂, dark, moisture added (open squares with dashed lines); air, dark, moisture added (open squares with solid lines); air, natural light-dark cycle, but no moisture added (starbursts with solid lines).