Elena Fukasawa Galvanese

Doutorado | 4° ano

elenagalvanese@gmail.com


Orientador

André Andrian Padial


Coorientadores

Luis Aubriot

Michele Burford

Possible Implications of phosphorus availability patterns on freshwater cyanobacterial growth at community level

The study of the maintenance of biological diversity implies studying species’ interactions, which interacts with the study of the relation between the environment and populations. As the environment is constantly changing, it is particularly important to evaluate how the organisms respond to changes in key environmental drivers, as well as the limits of responses. Intending to evaluate the impacts of distinct supplies of phosphorus (P) in freshwater cyanobacteria communities, we performed experiments with mono and mixed cultures of three species of cyanobacteria using 33P isotope. The experiments encompassed submitting deficient cultures to saturating and no saturating P additions. The same total P concentration was given either in one addition or divided in 10 times (i.e. pulses; hereafter 1P and 10P respectively). We measured the P uptake, the growth by using optical density at 750nm, and assessed the use of organic P through the alkaline phosphatase activity (APA) with fluorescence method in monocultures. The preliminary results showed different uptake rates, growth rates and APA among species. Beyond the expected reduction in APA as the exponential phase starts, we found reductions of APA in 1P treatment and increases in 10P along the growth curve. Despite the different physiological responses regarding APA, the growth rates were similar between 1P and 10P (except for one species). As the growth curve was not followed until the stationary phase, it is unsure if the biomass and/or APA would differ among treatments. The APA results are another evidence that the species might rely on organic and inorganic sources at different levels. Considering the APA results and the growth rates between treatments, we demonstrated how difficult is to directly link nutrient availability (concentration and quality) to population growth and community dynamics, mainly in models with fixed physiological parameters.