Periphytic algal community adaptive strategies in N and P enriched experiments in a tropical oligotrophic reservoir

Abstract

This study aimed at evaluating periphytic algae adaptive strategies, including size class, growth, and adherence forms, and the CRS functional groups model under nitrogen and phosphorus artificial enrichment in a Brazilian tropical shallow and oligotrophic reservoir. Four treatments were designed using enclosures (n = 3) filled with 185 L of reservoir water: control (no nutrient addition), P+ (isolated P addition, N-limiting condition); N+ (isolated N addition, P-limiting condition); and NP+ (combined addition, no limitation). N:P ratios were maintained throughout the experiment. Glass slides were used for periphyton growth, and sampling campaigns were carried out at short regular intervals (3–5 days) over a 31-day succession. Enrichment favored replacement of flagellates and loosely attached (mobile) forms by firmly attached mainly prostrate and entangled forms over succession. Isolated or combined P addition favored C–S-strategists green algae, whereas P limitation kept R-strategists over succession, promoting R-Cyanobacteria under high P limitation. Our results were supported by the species density and biovolume due to the dominance of small size classes (small-sized classes) in the community (nano and picoperiphyton). Overall, only the CRS strategies were more predictive of the experimental nutritional conditions.