Synergistic effects of nutrients and light favor Nostocales over non-heterocystous cyanobacteria

A. AGUILERA; L. AUBRIOT; R.O. ECHINIQUE; G.L. SALERNO; B.M. BRENA; M. PIREZ; S. BONILLA

HYDROBIOLOGIA

SPRINGER

Lugar: Berlin; Año: 2016

0018-8158

The recent increase of heterocystous cyanobacteria (Nostocales) blooms around the world has been explained by the combined effects of climate change and eutrophication.  According to nutrient stoichiometry and physiological differences between cyanobacterial  groups, the replacement of Nostocales over non-heterocystous species is favored when  dissolved inorganic nitrogen decreases. However, some studies show different trends. In  this work, we used microcosm experiments to evaluate the concomitant effects of light and  nutrient enrichment on the species composition and cyanotoxin concentration of  phytoplankton assemblages dominated by non-heterocystous filamentous cyanobacteria.   Three nutrient conditions (no addition, addition of phosphate, and nitrate and phosphate)  and two light intensities (40 and 80 µmol photon m-2 s-1) were assayed. Nostocales replaced non-heterocystous species in almost all treatments by the end of the study. This shift in community composition led to an increase in species diversity, even at high total  biovolume, contradicting the inverse general trend between biovolume and diversity. The highest saxitoxin concentrations were found in control treatments, which link toxin  production to nutritional stress. Nostocales showed higher phenotypic plasticity than non- heterocystous species in terms of changes in individual volume and growth rates. These  results help to understand the increasing predominance of Nostocales blooms in freshwaters  of temperate zones.