AVALIAÇÃO DO CRESCIMENTO, PADRÕES METABÓLICOS E CAPACIDADE FOTOSSINTÉTICA DE Microcystis panniformis Komárek et al. (CYANOBACTERIA) E Ankistrodesmus gracilis (Reisch) Korsikov (CHLOROPHYTA) EM FONTES DE NITROGÊNIO INORGÂNICAS E ORGÂNICAS

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The phytoplankton, constituted mainly of planktonic algae and cyanobacteria, is extremely important in the aquatic ecosystems since, besides being a food source for aquatic animals, it also produces oxygen. The cyanobacteria are becoming an important group mostly in eutrophic systems. Several hypotheses tried to explain the dominance of cyanobacteria and many emphasize the importance of the type of the nitrogen sources for their success. In this study we evaluated the effect of inorganic (nitrate and ammonium) and organic (arginine, glycine and urea) nitrogen sources on the growth, biochemical composition and photosynthetic capacity for the chlorophycean Ankistrodesmus gracilis and the cyanobacteria Microcystis panniformis, as well as the concentration of the cyanotoxin microcystin for the latter. The study was run in batch cultures on a WC medium with different nitrogen sources, one at a time. The cultures were maintained at a temperature of 20C and light intensity of 75 μmol de fótons.m-2.s-1 on a light/dark cycle of 12:12h. A growth curve was obtained through 15 days experiments and samples were taken at a two days interval. The biochemical composition (carbohydrate and protein) and the concentration of chlorophyll a and microcystin were measured at the end of seven days experiments (exponential growth phase). The measurement of the photosynthetic capacity was also measured after seven days. The results showed that both species had higher growth rates in ammonium than in nitrate. On the organic sources results were different between the two species. Final cellular density was higher in nitrate than in ammonium and showed similar and high concentration in the organic nitrogen sources. Chlorophyll concentration showed little variation, with higher values on glycine for both species. In general higher content of carbohydrate were found on organic sources for both A. gracilis and M. panniformis, and higher protein concentration on inorganic sources, except for A. gracilis in ammonium. The microcystin concentration was higher on the ammonium and urea treatments (with or without nickel). For both species, the photosynthetic capacity was xiii superior in nitrate than ammonium and on glycine than arginine. About the urea treatment with and without nickel, it was not possible to observe any difference between them, but generally urea showed lower growth rates, chlorophyll and protein content, and photosynthetic performance. Our results suggest that the organic nitrogen sources were able to allow growth of both the chlorophycean and the cyanobacteria. For the chlorophycean nitrate allowed higher production of protein relative to chlorophyll and carbohydrate than all other sources. The cyanobacteria when growing on inorganic sources also showed higher protein to chlorophyll and to carbohydrate ratios when compared to the organic sources.

ASSUNTO(S)

recursos hidricos 1. nitrogênio - teses. 2. fotossíntese - teses. 3. metabolismo - teses. i. universidade federal de ouro preto. ii. título.

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