Ocean's 16: Dynamical, evolutionary and molecular origins of Redfield ratio N : P = 16 in oceans.
By Dr Irakli Loladze, University of Nebraska-Lincoln, USA.
Tuesday, July 21, 2009
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Abstract
Among the biosphere's largest patterns is atomic nitrogen: phosphorus ratio (N : P) = 16 found throughout deep ocean; though N : P of individual phytoplankton species ranges from 6 to 60, the average N : P of plankton is also 16.
Discovered empirically by Redfield over 70 years ago, this pattern is crucial to carbon sequestration, climate change and biogeochemical cycling models. However, the rationale behind N : P = 16 is not known. Here, we show that N : P = 16 is the result of biogeochemical homeostasis that originates on a molecular scale while evolutionary forcing and feedback of upwelling amplify the pattern to the global scale. First, we show that when nutrients are replete, Redfield ratio stems from five fundamental molecular values, including N in amino acids, N and P in nucleotides.
Next, we construct a dynamical model that considers RNA:protein ratio as an evolutionary trait; it shows that when nutrients are limiting, an evolutionary stable strategy is for N : P of plankton to deviate toward N : P of the inflow. Finally, we show that upwelling of nutrients in our model provides a feedback that results in the convergence of N : P of plankton to Redfield ratio over geological times.
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