Complexity in oceanic photosynthesis

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Photosynthetic saturation of open PSII over 100 microseconds, simulating a fast repetition rate saturation phase transient measurement.

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Enhancement due to 'connectivity' between individual photosystems in this model, showing how cooperation between photosystems can in principle increase overall photosynthetic efficiency.

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» jpy_07-187_153404.pdf
Laney et al. J. Phycology, 2009

Many of the core aspects of light harvesting by phytoplankton (and all plants) are strongly nonlinear and difficult to model using typical, equation-based approaches. I developed a Monte Carlo approach for simulating photon capture and uptake by phytoplankton, in order to assess the dynamics of this initial, important step in phytoplankton photosynthesis. The results of this simulation are used to indicate particular combinations of model parameters that may lead to nonlinear enhancement of light harvesting, to answer the question of whether or not phytoplankton can find a 'sweet spot' in parameter space (Laney et al., J. Phycol., 2009).

The model represents a populations of photosystems within a model space (right), where each photosystem can be assigned different values of specific physiological properties related to light harvesting & photon capture (left). The Monte Carlo method is used to simulate how individual photons passing through the model space (representing sunlight) interact with the individual photosystems in the population.

The algorithm of this Monte Carlo simulation can be represented by a simple flowchart that determines the fate of each individual, incoming photon:

The model can be run to steady state, to determine how specific PSII structures and physiological combinations produce a given electron flow rate. It can also be run to assess the transient dynamics of this system, e.g., to replicate physiological transients such as would be produced experimentally with FRR fluorometry.


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