Periphyton microbial communities of artificial streams impacted similarly by distinct phosphorus enrichment patterns

Phosphorus (P) enrichment of stream water influences the diversity and composition of periphyton assemblages. However, P enrichment can vary temporally with the source of P and there is limited knowledge of the relative impacts of different enrichment patterns on periphyton communities. To address this knowledge gap, we conducted a 25-day mesocosm experiment using nine artificial streams exposed to three P enrichment loading patterns: unenriched, continuously enriched, or event enriched. Periphyton samples were collected from each stream at six time points during the experiment and high throughput sequencing of 16S and 18S rRNA genes was performed to characterize prokaryotic and eukaryotic microbial assemblages. Microbial community compositions of stream periphyton were similar by the end of the experiment for continuously and event enriched streams, and both treatments differed from end point microbial community profiles of unenriched mesocosms. This similarity among periphyton samples from enriched stream mesocosms was primarily due to the shared dominance of green algae (Desmodesmus) and Proteobacteria (Comamonadaceae) for eukaryotic and prokaryotic assemblages, respectively. Richness of both microbial assemblages declined with enrichment, regardless of loading pattern. In contrast, evenness only differed among eukaryotic assemblages, with lower evenness in the enriched streams compared to the unenriched. Overall, our data demonstrate that the amount of P enrichment, rather than pattern of enrichment, regulates periphyton microbial community composition. Management of P enrichment may thus benefit from targeting the most efficient way to reduce P loads regardless of source.