Figure 1

Acetylene reduction assay (ARA) as a proxy for N₂ fixation activity in intertidal microbial mats from Laguna Ojo de Liebre, Baja California, Mexico. Each time point measurement in each diel cycle experiment was conducted in triplicate (values in graphs depict the average of the three replicate measurements per time point per experiment including the s.d. as error bars). The horizontal bars indicate the incubation intervals of mat cores with acetylene in the ARA (incubation time was 3 h). (a) The diel cycle experiment was conducted in Guerrero Negro, Mexico, before the mats were transported to CA, USA, for detailed analysis. Two replicate diel cycle experiments are shown in the graph. (b, c) Diel cycle experiments of intertidal mats from Laguna Ojo de Liebre conducted in the laboratory at NASA Ames, CA, USA. Note the reduced N₂ fixation rates of controls (‘in situ water’) compared to the experiments in Guerrero Negro. (b) Experiment investigating the effect of DCMU on nitrogenase activity. (c) Experiment investigating the effect of molybdate on nitrogenase activity. No significant difference was detected in control ARAs conducted with in situ water versus artificial seawater (average±s.d.: 63±36 vs 64±36 C₂H₄ m⁻² h⁻¹, P=0.3386).