Spatiotemporal intermittence effect on periphyton microbial communities in a tropical drying river network.

Drying river networks (DRNs) are globally expanding ecosystems where hydrological intermittence, including surface-flow cessation and habitat fragmentation, profoundly shapes biodiversity, ecological functions, and biogeochemical processes. Despite growing knowledge, the role of microbial communities inhabiting periphyton in tropical DRNs remains poorly understood. Here, we conducted the first spatiotemporal metabarcoding assessment (16S & 18S V4 amplicon sequencing) of bacteria, phototrophs, and fungi in stream periphyton across the Cube Drying River Network, located in Ecuador's Chocó-Darién biodiversity hotspot. We sampled 20 reaches spanning perennial and intermittent sites during six campaigns across an intermittence gradient. Microbial α-diversity increased with drying, peaking at the highest intermittence (45%), with phototrophs and fungi exhibiting significant gains compared to wetter phases. Community β-diversity declined as intermittence intensified, indicating homogenization of assemblages under sustained hydric stress and restricted dispersal due to disconnection of surface flow. Variation partitioning showed that major dissolved constituents (e.g., Ca