Analysis of microbial mats metabolism with microsensors after incubation under different light sources

Since electrochemical microsensors became commercially available, experimental applications of this advanced technique attracts increasing attention from average limnologists. This work aims at sharing results of analysing metabolism in stratified communities from the Chiprana salt-lake (SE Spain) for three metabolism attributes, which are representative of photosynthesis and respiration. Microbial mats from this lake, the only permanent hypersaline one in Spain, were incubated until stabilization in aquariums under four light sources, i.e. indoor sunlight, a Carrefour 12 W fluorescent tube, and shadowed and unshadowed Osram Decostar 50 W halogen lamps. Photosynthetic active radiation (PAR) was measured with a Li-Cor LI-1000 datalogger and flat quantum sensor. Unisense MiniProfiler MP4 microsensors for dissolved oxygen (Clark), pH and redox potential were used to compare the adequacy of light sources for mat growth and development. Three vertical microprofiles per attribute and light treatment were performed (total height about 1 cm, measurement interval 50 µ), in randomly-selected locations throughout microenvironment surface. PAR values (µmol s-1 m-2) were lower under halogen than under fluorescent light (8,33 in shadowed and 15,59 in unshadowed, vs. 17,40 in fluorescent treatment). The highest PAR values were recorded under sunlight (478 µmol s-1 m-2). Absolute maximum mat metabolism was higher under shadowed halogen light (27,24 mg O2 L-1), but average maximum value for the three unshadowed locations was higher. However, dissolved oxygen in the later was most variable across depth among all treatments (coefficient of variation 211-246 %). These results show that light source attributes (intensity and PAR) do not show simple correspondence with metabolism attributes. The highest values of dissolved oxygen were recorded under light sources with the lowest PAR values, but not necessarily with the lowest light intensities. Despite this apparent prevalence of light quality, excessive intensity might explain differences between shadowed and unshadowed halogen treatments