Nutrientes e luz determinam a estrutura taxonômica e funcional da comunidade fitoplanctônica : uma abordagem experimental de oligotrofização.

Abstract

Light and nutrients are essential for phytoplankton. Factors affecting the availability of these resources may cause changes in the taxonomic and functional structure of these primary producers and consequently in ecosystems processes. In rivers, reservoirs return to the area, reducing nutrient concentration and increasing transparency in downstream regions. Used Reynolds Functional Groups (RFG) to test experimentally the factors the effects of light in conjunction with nutrient limitations (oligotrophic) on the phytoplankton structure. Tested the hypothesis that this status is negatively adjusted for growth (richness, biovolume, and growth rate). Collected phytoplankton in lakes of the Upper Paraná River Floodplain and subsequently exposed it to treatments (three replicates) with different combinations of resource availability (availability of light with limitation nutrient, limitation of light and disponibility of nutrients, limitation of light and nutrients without limitation of this factors). We collected samples in the beginning and after 10 days. The results indicated that the limitation of nutrients affected negatively the richness and the biovolume phytoplankton. The species richness and the RFGs were significantly limited by light availability conditions and limitation for nutrients (ANOVA). Light limitation conditions and nutrients available affects positively the taxons numbers dos RFGs F and J. The biovolume of RFG H1 and X1 were highest in all established conditions. The RFGs F and G presented growth ratio significantly in conditions the light conditions and nutrients (ANOVA). Showed that environmental with light available, however limited by nutrients selected RFGs (e.g H1 and X1) represented by species with traits that optimization the capitation of resource, as highest ration of surface/volume. Concluded that changes in the nutrients concentration and in the light available, entailed by reservoir and mutant, can decrease the phytoplankton functional diversity in downstream regions, that consequently can affect the primary production and interfere with the water chains.