Comparative Analysis of Bacterial Diversity and Functional Potential in Two Athalassohaline Lagoons in the Monegros Desert (NE Spain)

This study compared bacterial diversity and putative functionality between two saline lagoons, La Muerte and Salineta, in the Monegros desert ecosystem. Amplicon sequencing analysis revealed distinct taxonomic and functional patterns between the lagoons. Pseudomonadota dominated both systems, averaging 31.0% in La Muerte and 47.4% in Salineta, reflecting their well-documented osmotic stress tolerance. However, significant compositional differences were observed: Cyanobacteriota comprised 18.4% of La Muerte communities but remained below 1% in Salineta, while Bacteroidota showed higher abundance in La Muerte (16.6%) compared to Salineta (6.7%). Principal coordinate analysis demonstrated strong community differentiation between lagoons (Bray-Curtis dissimilarity <i>p</i> < 0.05). Functional profiling revealed contrasting metabolic capabilities: La Muerte communities showed enhanced autotrophic carbon fixation pathways (especially the Calvin-Benson cycle) and nitrogen cycling processes, while Salineta exhibited stronger denitrification signatures indicative of anoxic conditions. Carbohydrate indices suggested different organic matter quality and polymer composition between lagoons. La Muerte demonstrated significantly elevated stress response mechanisms compared to Salineta, which can be attributed to its ephemeral, shallow, and high evaporation rates that collectively generate more severe osmotic, thermal, and oxidative stress conditions for the sediment microbiota. These findings demonstrate that site-specific environmental factors, including hydroperiod variability and salinity dynamics, strongly influence microbial community structure and metabolic potential in saline wetland ecosystems.