Conversion and conservation of light energy in a photosynthetic microbial mat ecosystem

Abstract

Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (J abs ). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scattering-absorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with 499% of the absorbed light energy being dissipated as heat and o1% used by photosynthesis at J abs 4700 lmol photon m À2 s À1 (4150 J m À2 s À1). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014À0.047 O 2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at J abs 4700 lmol photon m À2 s À1 , they reached around 10% of the maximum values at depths 0À0.3 mm and progressively increased toward 100% below 0.3 mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.

Thermal effects of tissue optics in symbiont‐bearing reef‐building corals

“…Similarly, the heat budgets of intertidal invertebrates during air exposure sensibly ignore metabolic heat production, which is all but negligible when compared to irradiance, convection, and conduction (Helmuth 1998). Energy budgets in optically dense microbial mats also showed that heat dissipation from light absorption is predominant (Al-Najjar et al 2010). …”

Structure and function of natural sulphide-oxidizing microbial mats under dynamic input of light and chemical energy

“…Fluxes of incident light energy were estimated from the measured downwelling irradiance, assuming that the average energy content of photons of photosynthetically available radiation is 217.5 kJ (mol photons) − 1 (Al-Najjar et al, 2010). The fraction of the incident light energy absorbed by the cyanobacterial population in the mats was estimated from the measured reflectance of the mats (see Supplementary Information 1).…”

Effects of Climate Change and LUCC on Terrestrial Biomass in the Lower Heihe River Basin during 2001–2010

“…About 3.8ˆ10 24 J solar energy is annually absorbed by the surface and atmosphere of the Earth, 95.5% of which dissipates as the sensible and latent heat fluxes, only 4.5% is channeled into photosynthesis [6,7]. The photosynthesis using the photosynthetically active radiation (PAR) as the energy source is the only process by which carbon dioxide (CO 2 ) is converted into organic carbon and the solar energy is converted into chemical energy and stored as biomass [6,8].…”

“…About 3.8ˆ10 24 J solar energy is annually absorbed by the surface and atmosphere of the Earth, 95.5% of which dissipates as the sensible and latent heat fluxes, only 4.5% is channeled into photosynthesis [6,7]. The photosynthesis using the photosynthetically active radiation (PAR) as the energy source is the only process by which carbon dioxide (CO 2 ) is converted into organic carbon and the solar energy is converted into chemical energy and stored as biomass [6,8]. Once stored, the biomass can provide food for heterotrophic organisms and can be processed into usable energy such as renewable fuel or bioenergy, which has currently attracted great interest in the global energy scenario [6,[9][10][11][12][13][14].…”

“…Ecosystem services are tightly coupled with the availability of solar energy and its partition into energy fluxes in the heterogeneous landscape, which was dominated by heat dissipation on the expense of photosynthesis [1][2][3][4][5][6]. About 3.8ˆ10 24 J solar energy is annually absorbed by the surface and atmosphere of the Earth, 95.5% of which dissipates as the sensible and latent heat fluxes, only 4.5% is channeled into photosynthesis [6,7].…”