A simple light meter for measurements of PAR (400 to 700 nm) with fiber-optic microprobes: application for P vs E0 (PAR) measurements

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Journal Article
Aquatic Microbial Ecology, 1997, 13 pp. 197 - 207
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A simple portable light meter for use with fiber-optic microprobes was developed. The meter has a flat spectral quantum responsivity for 400 to 700 nm light (photosynthetically available radiation, PAR). With scalar irradiance microprobes connected to the meter, it was possible to directly measure photosynthetically available quantum scalar irradiance, E0(PAR), at <100 µm spatial resolution and over a dynamic range from <1 to >1300 µmol photons m-2 s-1. We used the new instrument for scalar irradiance measurements in microbial mats from a freshwater lake (Lake Stigsholm, Denmark) and from a hypersaline pond (Eilat, Israel). Combined measurements of quantum scalar irradiance by fiber-optic microprobes and oxygenic photosynthesis by oxygen microelectrodes made it possible to measure gross photosynthesis as a function of the prevailing scalar irradiance (P vs E0 curves) at distinct depths within an undisturbed hypersaline microbial mat of immotile unicellular cyanobacteria (Aphanothece spp.).
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