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Notes on “Linking physiology to ecology: towards a new generation of plankton models” by Allen and Polimene (2011)

“We start from the assumption that, in the marine planktonic environment, biogeochemistry and ecology evolve from physiology and not vice versa. This means that biogeochemistry and ecology are generated by a limited number of “physiological rules” such as photosynthesis, respiration, antioxidant response, autophagy etc. that are “prescribed” and common to all phytoplanktonic organisms. To avoid any misinterpretation of our statement, we need to carefully discriminate between the “physiological potential” and “physiological activity”. Life is bound by certain combinations of chemical reactions that manifest themselves as cell physiology. We define “physiological potential” as the underlying conserved processes (“genetic capacity”) which describe the generic chemical functions of all cells. The “physiological activity” refers to the chemical fluxes generated by the physiology as modified by species differences (genetic constrains), external environmental drivers and the interactions between the two. Essentially, we consider the physiological potential as the “potentiality” that the organisms have to grow and survive and the “physiological activity” the “implementation” of the “physiological potential”; photosynthesis is the generic “physiological rule”, the photosynthetic rate is the “physiological activity”. Consequently, considering the “physiological rules”, we can look at the phytoplankton as a single “generic” organism, while, on the basis of the physiological activity, we can account for phytoplankton diversity. It is on the basis of cellular “physiological activity” that the environment selects a particular species in a particular niche and is also through physiological activities that a single species can acclimate to changing environmental conditions. Given an accurate description of the main physiological mechanisms (the “physiological potential”), it should be possible to create as emergent properties a feedback (circular) mechanism accounting for physiological activity, biogeochemistry and ecology.”

The idea is to create a generic cell, common to all phytoplankton species, that has the potentiality of different physiology. Depending on the environment and other factors, the expression of each physiology will differ from cell to cell, and diversity and species would arise automatically, as an emergent properties, and would be a function of the environment, fitting our conceptual view of ecosystem.

“The succession between diatoms and dinoflagellates can be viewed as an emergent property generated from the physiological landscape. Although the underlying physiology is ubiquitous (common to both groups), the physiological activity, which accounts for the biogeochemical differences between the two groups, is different. All phytoplankton have antioxidant responses allowing a certain grade of acclimation, but some groups can do it better than others. In other words, the emergent property arises from a different implementation (the “physiological activity”), which is driven by environmental forcing (light, nutrient deficiency etc.), of the same, generic, “physiological potential” (the antioxidant response).”

“PFT modellers generally have been focusing the model development at the level of organization, where they have the most empirical information. Unfortunately, this information lies at an intermediate level of organization lying between intra- and inter-cellular processes rather than at the levels at which emergence actually occurs, i.e. at the intra- and inter-cellular levels.”