Microscale Vertical Profiles of N2 Fixation, Photosynthesis, O2, Chlorophyll a, and Light in a Cyanobacterial Assemblage

AUTOR(ES)

Dodds, Walter K.

RESUMO

Profiles of 15N2 fixation, O2 production (gross photosynthesis), O2 concentration, chlorophyll a concentration, and photon fluence rates were measured with 50-μm resolution in colonies of the heterocyst-forming cyanobacterium Nostoc parmelioides. Microelectrode measurements were made after 20 h of incubation under 15N2 gas. Colonies were frozen, and 50-μm sections were prepared by using a freezing microtome and analyzed for 15N enrichment and chlorophyll a concentration. Colonies exhibited steep spatial gradients in rates of gross photosynthesis, O2 concentration, and irradiance, with the highest values generally occurring at the surface. O2 concentration, photosynthesis, and irradiance all showed positive correlations, but chlorophyll a concentrations varied independently of photosynthesis and irradiance. Forty-four percent of the variation in 15N incorporation was explained by gross photosynthesis (a positive correlation) when incorporation of 15N was expressed per unit of biomass (chlorophyll a).

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