Efeitos da limitação de fósforo na eficiência fotossintética, na morfologia e no crescimento de Cylindrospermopsis raciborskii

Abstract

Cylindrospermopsis raciborskii is a filamentous cyanobacteria able to fix N2 and has been object of many studies because of its potential toxicity and wide ecophysiologic adaptability. Its success is ascribed to, among other things, its shade adaptability, high affinity for phosphorus besides being able to store this nutrient. Since there has been many recent blooms of C. raciborskii around the world it become indispensable to know the ecology and physiology of these species. These work intent to evaluate the effects of phosphorus limitation on photosynthetic efficiency, morphology and growth of C. raciborskii. The species showed a low photosynthetic efficiency (α) under natural conditions and an even lower α after P limitation, which were attributed to its low chlorophyll a content. However, C. raciborskii had a high photosynthetic capacity (Pmb), before and after P limitation period. These ability is essential for the development of blooms. P limitation also reduced the growth and induced extreme morphological changes, such as: low surface:volume ratio, formation of akinetes, trichomes with different cell sizes proving the relevance of these nutrient on morphology of the species. These morphological changes had also influenced the low α found in these work. Our results suggest prudence on the taxonomic identification of C. raciborskii based on morphological characteristics and they demonstrate that the discontinuity on P load to aquatic ecosystems subject to C. raciborskii blooms does not assure that the blooms will not happen.