New cell-based model of photosynthesis and photo-acclimation: accumulation and mobilisation of energy reserves in phytoplankton

Abstract

In this study, we present a new model of acclimation to light under nutrient-replete conditions based on the photo-acclimation model by Geider et al. (1998; Limnol Oceanogr 43:679-694). Rather than being solely carbon (C)-based, the new model employs the cell as the basic unit, which makes it more amenable for application in individual-based (Lagrangian) modelling approaches. The model differentiates between a functional C pool which also contains nitrogen (N) and an energy reserve pool which does not contain N. The cell-specific light-saturated photosynthetic rate is assumed to scale with the size of the functional pool, and the light-limited photosynthetic rate with the cellular chlorophyll content. Through the explicit inclusion of a C (energy) storage pool, an improved regulatory term for chlorophyll synthesis, and the addition of an optional acceleratory term, the dynamics of the model in comparison to the original model could be improved. This is demonstrated by observations during a light-shift experiment on the diatom Skeletonema costatum.

Modelling the effect of vertical mixing on bottle incubations for determining in situ phytoplankton dynamics. I. Growth rates

“…We extend the RG I model from Ross & Geider (2009) to account for photoinhibition using a similar approach as in Cianelli et al (2004) except that we apply the inhibition primarily to the initial slope of the photosynthesis-light curve, α Chl , and only once the damage becomes more substantial also to the maximum cellbased carbon production, P cell max . The proportion of still functional reaction centres, ϑ, depends on the damage probability, k d , and the recovery rate, k r , of the D1 protein as (cf.…”

“…The cell-specific light-saturated photosynthetic rate is assumed to scale with the size of the functional pool, and the light-limited photosynthesis rate with the cellular chlorophyll content. The model has been validated against data from light shift experiments on Skeletonema costatum (Anning et al 2000, Ross & Geider 2009) and the values of the growth and acclimation parameters we use in this study are representative of this diatom. As we are not concerned about absolute growth rates but content ourselves with comparative analyses, the results presented in this study are insensitive to small changes in these parameter values and are therefore deemed to be valid for a wider range of phytoplankton species.…”

“…The biological model used in the simulations is based on the RG I model in Ross & Geider (2009). Rather than being solely carbon-based, the biological model employs the cell as the basic unit, which is a more natural choice for use in individual-based modelling approaches such as this one.…”

“…Han 2002, Cianelli et al 2004: (6) where σ PSII is the absorption cross-section of Photosystem II (PSII), a Chl the Chl specific absorption coefficient and φ max the maximum quantum yield of photosynthesis (Table 1). The values chosen for k d and k r from Table 1 Chl was determined experimentally for Thalassiosira pseudonana (Ross & Geider 2009). The parameter ϑ describes the proportion of still functional PSII reaction centres (RCII) (0 ≤ ϑ ≤ 1) with the extremes of ϑ = 1 corresponding to zero inhibition (i.e.…”

“…We therefore do not re-iterate the entire model description but limit our description to the new and modified parts of the model. A complete set of the biological model equations, including the unchanged parts from the original RG I model, is contained in Appendix 1 (see Ross & Geider 2009 for additional information).…”