Heterogeneity of Oxygen Production and Consumption in a Photosynthetic Microbial Mat as Studied by Planar Optodes

Abstract

By applying planar optodes and imaging techniques to a benthic photosynthetic mat, we demonstrated an extensive vertical and horizontal variation in O2 concentrations, O2 consumption, and O2 production. In light, the oxic zone could be divided into three horizons: 1) an upper zone dominated by diatoms that had a moderate net O2 production, 2) another zone dominated by Microcoleus‐like cyanobacteria with a high net O2 production, and 3) a lower zone with disintegrating microalgae and cyanobacteria with a high O2 consumption rate. From the O2 images, the net O2 production/consumption was calculated at a spatial resolution of 130 μM. This allowed us to identify microsites with high rates of O2 turnover within the photic zone. Sites with high net O2 consumption (>1.5 nmol·cm−3·s−1) were typically situated next to sites with a relatively high net production (>2 nmol·cm−3·s−1), revealing a mosaic in which the highest O2 consumption sites were surrounded by the highest O2 production sites. This suggested a tight spatial coupling between production and consumption of O2 within the photic zone. Light stimulated the O2 consumption within the photic zone. At irradiances above 400 μmol photons·m−2·s−1, the stimulated O2 production was almost completely balanced by enhanced O2 consumption at microsites exhibiting net consumption of O2 even at maximum irradiance (578 μmol photons·m−2·s−1). Our observations strongly supported the idea that light‐stimulated respiration was caused by stimulated heterotrophic activity fueled by organic carbon leakage from the phototrophs. Despite microsites with high net O2 consumption, anoxic microniches were not encountered in the investigated mat. Images of gross photosynthetic rates also revealed an extensive horizontal variation in gross rates, with microsites of low or no photosynthesis within the otherwise photic zone. Calculations based on the obtained images revealed that at maximum light (578 μmol photons·m−2·s−1), 90% of the O2 produced was consumed within the photic zone. The presented data demonstrate the great potential offered by planar optode for studies of benthic photosynthetic communities.

Eutrophication in shallow coastal bays and lagoons: the role of plants in the coastal filter

“…Photosynthesis and respiration by benthic microalgae in the top few millimeters of the sediments cause large diel variations in oxygen concentrations and penetration depth, dissolved inorganic carbon (DIC) concentrations and pH (e.g. Glud et al 1999). The steep and dynamic oxygen gradients created by benthic microalgal activity affect the vertical position and rates of redox-sensitive processes such nitrification, denitrification, DNRA, anammox and reduction of Mn, Fe and sulfate (e.g.…”

Primary Production in the Ocean

“…Optodes work by using fluorescence quenching by oxygen of a luminophore. The intensity of fluorescence is inversely proportional to the O 2 partial pressure at the luminophore (Glud et al, 1999). For example, Glud et al (1999) used the luminophore ruthenium (III)-Tris-4,7-diphenyl-1,10-phena-throline, which absorbs blue light (450 nm), with the intensity of the emitted red light (650 nm) decreasing with increasing O 2 partial pressure.…”

“…Unlike Clark-type oxygen electrodes, optodes do not consume oxygen. Two designs of optodes are used in photosynthesis measurements: optodes that are used in a similar way to oxygen microelectrodes (Miller & Dunton 2007), and planer optodes that produce a two-dimensional image of oxygen concentrations (Glud et al, 1999(Glud et al, , 2001). Miller & Dunton (2007) used a micro-optode to measure photosynthesisirradiance curves for the kelp Laminaria hyperborea.…”

“…Miller & Dunton (2007) used a micro-optode to measure photosynthesisirradiance curves for the kelp Laminaria hyperborea. Planar optodes have been used to produce images of oxygen concentrations across the sediment-water interface in sediments colonized by photosynthetic biofilms (Glud et al, 1999(Glud et al, , 2001. As planar optodes produce a two dimensional image, multiple oxygen profiles can be extracted from a single measurement (Glud et al, 2001).…”

“…As planar optodes produce a two dimensional image, multiple oxygen profiles can be extracted from a single measurement (Glud et al, 2001). Moreover, the light-dark shift method can be used to measure gross photosynthesis rates (Glud et al, 1999).…”