Toward autonomous measurements of photosynthetic electron transport rates: An evaluation of active fluorescence‐based measurements of photochemistry

<jats:title>Abstract</jats:title><jats:p>This study presents a methods evaluation and intercalibration of active fluorescence‐based measurements of the quantum yield ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0001.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0001" />) and absorption coefficient ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0002.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0002" />) of photosystem II (PSII) photochemistry. Measurements of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0003.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0003" />, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0004.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0004" />, and irradiance (<jats:italic>E</jats:italic>) can be scaled to derive photosynthetic electron transport rates ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0005.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0005" />), the process that fuels phytoplankton carbon fixation and growth. Bio‐optical estimates of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0006.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0006" /> and <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0007.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0007" /> were evaluated using 10 phytoplankton cultures across different pigment groups with varying bio‐optical absorption characteristics on six different fast‐repetition rate fluorometers that span two different manufacturers and four different models. Culture measurements of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0008.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0008" /> and the effective absorption cross section of PSII photochemistry ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0009.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0009" />, a constituent of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0010.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0010" />) showed a high degree of correspondence across instruments, although some instrument‐specific biases are identified. A range of approaches have been used in the literature to estimate <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0011.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0011" /> and are evaluated here. With the exception of ex situ <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0012.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0012" /> estimates from paired <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0013.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0013" /> and PSII reaction center concentration ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0014.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0014" />) measurements, the accuracy and precision of in situ <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0015.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0015" /> methodologies are largely determined by the variance of method‐specific coefficients. The accuracy and precision of these coefficients are evaluated, compared to literature data, and discussed within a framework of autonomous <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0016.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0016" /> measurements. This study supports the application of an instrument‐specific calibration coefficient ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0017.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0017" />) that scales minimum fluorescence in the dark ( <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0018.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0018" />) to <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0019.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0019" /> as both the most accurate in situ measurement of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0020.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0020" />, and the methodology best suited for highly resolved autonomous <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/lom310014-math-0021.png" xlink:title="urn:x-wiley:15415856:media:lom310014:lom310014-math-0021" /> measurements.© 2014 Association for the Sciences of Limnology and Oceanography</jats:p>