doctoralThesis
Mixotrofia do fitoplâncton em um gradiente de luz e nutrientes
Fecha
2019-04-26Registro en:
COSTA, Mariana Rodrigues Amaral da. Mixotrofia do fitoplâncton em um gradiente de luz e nutrientes. 2019. 96f. Tese (Doutorado em Ecologia) - Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, 2019.
Autor
Costa, Mariana Rodrigues Amaral da
Resumen
Precipitation events and water level fluctuations are environmental factors that affects
aquatic ecosystem functioning influencing phytoplankton dynamic and their resources.
Nutrient availability and trophic state of arid and semi-arid regions are controlled by
quantity and rain periodicity. Future climate scenario predicts an increase in intensity
and frequency of droughts in semi-arid regions. Drought leads to water level reduction
and consequently increase nutrients concentrations, turbidity, salinity and conductivity,
favoring cyanobacteria blooms. However, recent studies shows that mixotrophic algae
can be better competitors under more extreme conditions, such as prolonged periods of
droughts. Mixotrophic organisms play important role as producers and consumers
reflecting in the structure of food webs. In this work, we evaluate the effect of
precipitation gradient in semi-arid region on the structure of phytoplankton community
based on a trait-based approach. We confirm the hypothesis that in dry period the main
phytoplankton traits are related to a high cyanobacteria biomass (nitrogen fixation,
filaments, coloniality), however, in extremely drought periods with critical water level,
cyanobacteria collapse and shifts the dominance to mixotrophic algae. To confirm that
the reduction on light availability caused by sediment resuspension was the main factor
on phytoplankton pattern, we performed laboratory experiments with competition
between cyanobacteria and a mixotrophic species, manipulating light and sediment
addition in systems with high levels of nutrients. Besides this, we also performed
grazing experiments to estimate bacterivory by flagellate algae in distinct light and
nutrients conditions and propose new methodologies to facilitate ingestion rates
quantification. Our study shows the importance of mixotrophic algae in eutrophic
environments, such as semi-arid systems affected by hydric deficit, and compare
methodologies in order to facilitate bacterivory rates quantification, allowing a better
knowledge about this kind of mixed nutrition. Therefore, research about mixotrophy
implies in paradigmatic changes in how we understand aquatic food webs nowadays, in
particular this is even more critic when it links to shifts in environmental conditions in a
changing climatic world.