Periphytic algae of subtropical Andean streams in Argentina along an altitudinal gradient: a taxonomic and functional trait approach

Abstract

Abstract: Aim The research aimed to determine how environmental variables and seasonal hydrology influence biological organization by integrating taxonomic metrics with functional ecology. Methods Six streams were sampled during summer and winter. Physicochemical parameters were measured alongside periphytic algae collection to analyze density, diversity (Hill numbers), and functional traits (size, mucilage, and siliceous walls). Multi-table multivariate ordination and co-inertia models integrated these datasets across altitudinal strata and seasonal periods. Results The community (147 taxa, predominantly diatoms) is governed by a dual regulatory regime. Winter low-water periods promoted mature biofilms with higher diversity and biomass due to bed stability, whereas summer floods acted as a disruptive physical disturbance (scouring) that reset successional stages. The altitudinal gradient operated as a deterministic filter, establishing a distinct spatial segregation: higher altitude streams (lower temperatures, higher current velocity) favored specialized traits like silica cell walls, while low and mid-altitude sites (higher mineralization and phosphates) favored high biovolume and mucilage production. Conclusions The structural and functional organization of periphytic algae assemblages is shaped by a dual regime of spatial and temporal filters. This study provides the first functional baseline for the region, which is crucial for understanding ecosystem stability in Andean lotic systems under climate variability.