Light-enhanced oxygen respiration in benthic phototrophic communities

Abstract

ABSTRACT. Two microelectrode s t u d~e s demonstrate the effect of light intensity and photosynthesis on areal oxygen respiration in a hypersaline mat at Guerrero Negro, Mexico, and in an intertidal sediment at Texel, The Netherlands. The hypersaline mat was studied in the laboratory at light intensities of 0, 10, 25, 50, 100, 200, and 500 pE m-2 S -' using the light-dark shift technique to measure gross photosynthesis rates. Areal gross photosynthesis increased from 0 to 31.3 nmol O2 cni-' m i n ' and areal net photosynthesis increased from -3.9 to 16.7 nmol O2 cm-' min-' with increasing light intensities. Areal respiration, calculated from the difference between areal gross and areal net photosynthesis, increased from 3 9 to 14.4 nmol O? cin-Z min-l with increasing surface irradiance. This light-enhanced areal respiration was related to an increase in oxygen penetration depth from 0.2 to 2.0 mm, thus expanding the volume of sediment involved in oxygen respiration beneath the mat surface. The mean rate of oxygen respiration per volume of mat remained constant at a rate of -100 nmol O2 min-l. Oxygen profiles for the intertidal sediment were recorded in s~t u during the day at prevailing light intensities. A l-dimensional diffusion-reaction model was used to estimate gross photosynthesis and oxygen resplration per volume of sediment, as well as the euphotic depth and the s e d i m e n t -~d t e r interface concentration of oxygen. Areal gross photosynthesis ranged from 9.7 to 26.3 nmol 0, cm-' min-' and areal net photosynthesis ranged from 1.1 to 8.1 nmol O2 cm-' mln-l, both showing maximum values in the early afternoon. Areal respiration ranged from 8.1 to 18.2 nn~ol 0, cm-l min.' and showed a good positive linear correlation w~t h areal gross photosynthes~s ( R = 0.97, n = 9 ) . The enhanced areal respiration In the intertidal sediment was due to an lncrease in mean resp~ratlon per volume of sedlment from 18.5 to 52 nmol O L c m 7 m i n ' . The oxygen penetration depth only varied between 3.5 and 4.3 mm. Both studies thus indicate that areal respiration is enhanced significantly with increasing light intensities due to increased areal gross photosynthesis By assumlng that areal respiration in darkness is equal to areal respiration in the l~g h t , bell jar incubations would have underestimated areal resplration i.n the light 3.7-fold and areal gross photosynthesis 1.5-fold for the hypersaline mat and 10.7-and 2.6-fold for the intertidal sediment.

Irradiance Regulation of Photosynthesis and Respiration in Modern Marine Microbialites Built by Benthic Cyanobacteria in a Tropical Lagoon (New Caledonia)

“…Lightenhanced respiration can also be a consequence of downward migration of cyanobacterial filaments in microbialites, because it increases the diffusion distance of oxygen to the water column. As a result, the residence time of oxygen in the photic zone is increased, which stimulates R phot and thus reduces NP [17]. While downward migration appears as a very good strategy to evade the potentially inhibiting surface light intensities, the trade-off is that cells become increasingly separated from the water column, which acts as a sink for oxygen.…”

Temperature effects on respiration and photosynthesis in three diatom-dominated benthic communities

“…Sediment porosity (φ) was determined by core slicing and subsequent drying, but resulted in underestimated values due to an unavoidable loss of water in the relatively sandy sediment (data not shown). Therefore, porosity was instead estimated from the ratio between the O 2 concentration gradient measured immediately above and below the sediment surface (Glud et al 1995, Epping & Jørgensen 1996. In addition, porosity was estimated from resistivity measurements according to Klinkenberg (1951) and Ullman & Aller (1982).…”

“…Temperature studies of aerobic activity based on traditional bell jar approaches can easily be misinterpreted, as they do not account for changes in O 2 penetration depth (Epping & Jørgensen 1996). Further, it is to be expected that data from slurry samples can be biased due to changes in the benthic community structure and in the environmental controls.…”

“…Studying the temperature response of intact benthic microbial communities is complicated by the simultaneous impact on physical and chemical controls, and by the fact that benthic microbial communities host a complex phototrophic and heterotrophic diversity (Revsbech et al 1981, Epping & Jørgensen 1996, Fenchel & Glud 2000. Temperature studies of aerobic activity based on traditional bell jar approaches can easily be misinterpreted, as they do not account for changes in O 2 penetration depth (Epping & Jørgensen 1996).…”

“…3) (e.g. MacIntyre & Cullen 1995, Epping & Jørgensen 1996. Based on measured O 2 profiles in darkness, specific consumption rates were calculated for each zone, as R dark,vol,prod and R dark,vol,nprod , respectively.…”