Fig. 6.

Effects of chemical conditions on nitrogenase activity of microbial mats

Acetylene-reducing activity was measured using dispersed microbial mats in artificial hot spring water without Na₂S under the following conditions: “under argon gas”, “under H₂:CO₂ (4:1, v/v) gas”, “under H₂ gas”, and “under H₂:CO₂ (4:1, v/v) gas in artificial hot spring water containing no sodium sulfate”. Error bars represent the standard deviation of three replicates. Asterisks denote significant differences between complete (sample 2) and incomplete conditions (P values <0.05).