Predominance of deterministic microbial community dynamics in salterns exposed to different light intensities

While the dynamics of microbial community assembly driven by environmental perturbations have been extensively studied, our understanding is far from complete, particularly for light-induced perturbations. Extremely halophilic communities thriving in coastal solar salterns are mainly influenced by two environmental factors—salt concentrations and high sunlight irradiation. By experimentally manipulating light intensity through the application of shading, we showed that light acts as a deterministic factor that ultimately drives the establishment of recurrent microbial communities under near-saturation salt concentrations. In particular, the stable and highly change-resistant communities that established under high-light intensities were dominated (>90% of metagenomic reads) by Haloquadratum spp. and Salinibacter spp. On the other hand, under 37-fold lower light intensity, different, less stable and change-resistant communities were established, mainly dominated by yet unclassified haloarchaea and relatively diverse photosynthetic microorganisms. These communities harboured, in general, much lower carotenoid pigment content than their high-irradiation counterparts. Both assemblage types appeared to be highly resilient, re-establishing when favourable conditions returned after perturbation (i.e. high-irradiation for the former communities and low-irradiation for the latter ones). Overall, our results revealed that stochastic processes were of limited significance to explain these patterns.