Net photosynthetic growth as controlled by dynamic light regimes

Hewes, CD.  2017.  Net photosynthetic growth as controlled by dynamic light regimes. Journal of Plankton Research. 39:930-942.

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The photosynthetic response of the marine diatom Thalassiosira pseudonana to a matrix of dynamic light regimes is described. Ash-free dry weight and chlorophyll-a were measured as a function of dynamic irradiance having maximum intensities of 250, 500, 1000 and 2000 μmol photons m−2 s−1 with lengths of day being 6, 9, 12, 18 and 24-h periods. Incident irradiance followed a Gaussian (normal) distribution, which provided a statistical standard for the integrated quantum flux into a 20 cm water column. The matrix of conditions resulted with growth occurring in three groups (low, high and intermediate light) as a function of the amount for residual irradiance estimated at the mixing depth of 20 cm. The low light group displayed shade-limited (“linear” from self-shading), and the high light group displayed light-limited (“exponential” with no self-shading) phases of the light-controlled growth dynamic. For the same range of integrated daily incident irradiances, cultures growing under the phase of “linear” growth had higher biomass yields per quantum than cultures growing under an “exponential” phase of the growth dynamic. The difference in net quantum efficiency due to phase of the growth dynamic entails the relationship between photic zone and mixing depth, and provides a new perspective for interpreting Sverdrup's Critical Depth Model.