Nitrogen fixation patterns displayed by cyanobacterial consortia in Alchichica crater-lake, Mexico

Alchichica is a saline crater-lake located in Mexico. Tufa grows on its periphery and a wind-driven Nodularia cf. spumigena bloom occurs annually. Fixation rates were assayed by the acetylene reduction method. Here, we describe the patterns of nitrogen fixation on two tufa forms before, during and after the bloom, as well as those from the planktonic cyanobacteria. We also analyzed the effect of ultraviolet radiation (under 390 nm) on the nitrogen fixation rates. Tufa showed light-stimulated nitrogen fixation, while N. cf. spumigena peaks in early morning and midnight. Both tufa forms diminished their nitrogen fixation rates after the planktonic bloom. UV radiation affected negatively nitrogen fixation rates in all forms.