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bioRxiv · 10.64898/2026.10.04.756594

Depth-Resolved Microbial Community Structure and Phosphorus Deficiency Across a 34-cm Mat-Sediment Core in Poza Roja 2, Cuatrocienegas

Gonzalez-Sanchez, A.·Ibarra-Arzave, G.·Paniagua-Vargas, A.·Garcia-Oliva, F.·Olmedo-Alvarez, G.
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Abstract

Stratified benthic deposits offer crucial modern analogs for Precambrian biogeochemical dynamics, yet whether the vertical organization of deep sedimentary columns reflects depositional history, present-day geochemical conditions, or both remains poorly understood, particularly under extreme oligotrophy. Here, we present a depth-resolved exploratory survey of a continuous 34-cm sediment core partitioned into 11 discrete horizons (L1 to L11) from Poza Roja 2, an alkaline, sub-hypersaline pond in the Cuatro Cienegas Basin, Mexico. Integrating physical stratigraphy, organic carbon and nutrient stoichiometry, and 16S rRNA gene metabarcoding, we evaluated down-core microbial community structure alongside acute phosphorus scarcity. Molar C:Po and N:Po ratios exceeded canonical Redfield proportions (106:16:1) in every layer, by up to 48.5-fold and 87.8-fold, respectively, both peaking in layer L4. Unconstrained ordination (PCoA) and hierarchical clustering grouped the layers into three compositional zones: upper (L2-L4), intermediate (L5-L6), and basal (L8-L11), with L1 and L7 occupying transitional positions. Archaea accounted for 31.0% of prokaryotic reads, ranging from 8.3% (L5) to 43.7% (L9), and were dominated by SM1-50 (Thermoplasmatota) and Halobacteriota. The phototrophic heliobacterium Heliorestis peaked in the intermediate zone (47.6% of bacterial reads in L6). Constrained Redundancy Analysis models lacked statistical significance (P >= 0.12), highlighting the exploratory nature of a single core (n = 11). This pilot characterization provides a baseline for understanding deep biogenic archives under severe nutrient limitation.

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Gonzalez-Sanchez, A., Ibarra-Arzave, G., Paniagua-Vargas, A., Garcia-Oliva, F., Olmedo-Alvarez, G.. 2026-10-05. Depth-Resolved Microbial Community Structure and Phosphorus Deficiency Across a 34-cm Mat-Sediment Core in Poza Roja 2, Cuatrocienegas. https://doi.org/10.64898/2026.10.04.756594

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