The role of the heterocyte in the ecology of two bloom forming nitrogen fixing cyanobacteria

YEMA L.; LITCHMAN E.; DE TEZANOS PINTO P.

Granada

Congreso; Aquatic Science Meeting; 2015

Association for the Sciences of Limnology and Oceanography (ASLO)

In nitrogen fixing cyanobacteria the trait of nitrogen fixation (heterocyte) usually favors blooms in situations with low nitrogen, yet blooms can also occur at high nitrogen. We studied the role of the heterocyte in the ecology of two species (Dolichospermum flos?aquae and Cylindrospermopsis raciborskii) which have contrasting position of the heterocyte in its filaments. We exposed monocultures to contrasting nitrogen (0 and 1000 μmol/L) and phosphorous (2 and 15 μmol/L) concentrations, for 4 weeks. In both species nitrogen fixation occurred (range 22-37 μmol/L d-1) only in the absence of nitrogen, coinciding with high heterocyte density. D.flos aquae (heterocytes develop intercalary in the filament) achieved high biomass regardless of nitrogen availability, yet filaments were longer when heterocytes developed. C. raciborskii (heterocytes develop at the end of the filament) achieved little biomass when relying on fixation, and its filaments were extremely short. But, at nitrogen sufficiency, it achieved high biomass and long filaments;also heterocytes were expressed (but no fixation occurred). Heterocyte position may explain the contrasting ecologies of D. flos aquae and C. raciborskii (biomass, filament length, heterocyte expression).