Ecological aspects of cyanobacteria from the rice fields of Corrientes (Argentina)

Abstract

Nitrogen-fixing cyanobacteria are relevant organisms in rice fields. Their use as biofertilizers for this crop is well developed in Asia, where industrial fertilizers are scarcely available. In the rice fields of Corrientes, Argentina, these fertilizers are used abundantly, with an increase in yield but at the cost of ammonium and nitrate pollution in the local water supplies which are mainly from Paraná River.

In order to avoid this nuisance, and to establish a sustainable cropping system, the use of cyanobacteria as an alternative or complementary nitrogen source is proposed here. For this report, we studied cyanobacterial community composition in two ecosystems, together with some environmental factors that can regulate their growth and enzymatic activity.

The most representative strains belong to the genera Lyngbya and Microcystis, present in almost all samples; other important genera include Oscillatoria, Anabaena, Chroococcus and Plectonema. Apart from Anabaena,other nitrogen-fixing strains found in Corrientes belonged to the genera Gloeothece, Nostoc and Calothrix. In many of them, SOD, catalases and other enzymes related to nitrogenase protection were studied for their potential use as biofertilizers. Tests with triphenyl tetrazolium chloride were conducted to localize the sites of nitrogen fixation.