Abstract
Abstract. Light-use efficiency defines the ability of primary producers to convert sunlight energy to primary production and is computed as the ratio between the gross primary production and the intercepted photosynthetic active radiation. While this measure has been applied broadly within terrestrial ecology to investigate habitat resource-use efficiency, it remains underused within the aquatic realm. This report provides a conceptual framework to compute hourly and daily light-use efficiency using underwater O2 eddy covariance, a recent technological development that produces habitat-scale rates of primary production under unaltered in situ conditions. The analysis, tested on two benthic flux datasets, documents that hourly light-use efficiency may approach the theoretical limit of 0.125 O2 per photon under low-light conditions, but it decreases rapidly towards the middle of the day and is typically 10-fold lower on a 24 h basis. Overall, light-use efficiency provides a useful measure of habitat functioning and facilitates site comparison in time and space.
Highlights
1.1 Light-use efficiencyGross primary production can be formulated as the product of incident photosynthetic active radiation (PAR), the fraction of absorbed PAR, and the light-use efficiency (LUE), that is GPP = PAR × fAPAR × LUE (Monteith et al, 1977)
Phytoplankton studies typically investigate the quantum yield of photosynthetic production (Falkowski, 1992), whereas benthic studies have examined LUE on the microscale to quantify energy budgets of photosynthetic microbial mats and symbiont-bearing corals (Al-Najjar et al, 2010, 2012; Brodersen et al, 2014). These microscale measurements reveal that most (>80 %) of the incident solar energy is dissipated as heat, and conservation by photosynthesis typically is
Despite the fluxes originating from different parts of the sea floor, the flow direction did not have a substantial impact on hourly GPP, indicating that the eddy covariance measurements adequately integrated over habitat patchiness (Fig. 2)
Summary
Phytoplankton studies typically investigate the quantum yield of photosynthetic production (Falkowski, 1992), whereas benthic studies have examined LUE on the microscale to quantify energy budgets of photosynthetic microbial mats and symbiont-bearing corals (Al-Najjar et al, 2010, 2012; Brodersen et al, 2014). These microscale measurements reveal that most (>80 %) of the incident solar energy is dissipated as heat, and conservation by photosynthesis typically is
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