Modeling Net Growth of Phaeocystis antarctica Based on Physiological and Optical Responses to Light and Temperature Co-limitation

Tiffany A Moisan,B Greg Mitchell

doi:10.3389/fmars.2017.00437

Abstract

Temperature and light are fundamental environmental variables which regulate phytoplankton growth rates when nutrients are in excess. For polar coastal oceans that are undergoing changes in sea ice cover and warming, light and temperature are particularly important for bloom dynamics. Using colonial Phaeocystis antarctica cultures grown at steady-state, we assessed the combined effect of these two environmental controls on net growth rate (n), chlorophyll-specific absorption of light (a*ph ()), and quantum yields for growth (). Specific net growth rates (n) varied from 0.04 to 0.34 day-1 within a matrix of light and temperature ranging from 14 to 542 mol quanta m-2 s-1 and –1.5 to 4C. Values of a*ph () varied significantly with light but only slightly with temperature. Values of  ranged from 0.003 to 0.09 mol C (mol quanta absorbed)-1 with highest values at low light and 4oC. For excess irradiances or low temperatures where growth rate is inhibited, quantum yields were low. The low μ values are attributed both to increased absorption by photoprotective pigments compared to photosynthetic pigments and thermodynamic control of dark reaction enzymes. The systematic changes in photophysiological properties of P. antarctica in relation to temperature and light were used to develop a series of nested light- and temperature-dependent models for n, a*ph (), and . A model for a*ph (300-700 nm) was developed that takes into account the systematic changes in a*ph () due to pigment packaging effects and cellular concentrations of chlorophylls and photoprotective pigments. Also, a model for  was developed based on a cumulative one-hit Poisson probability function. These model parameterizations for absorption and quantum yield are combined into an overall model of net growth that can be applied easily to Phaeocystis antarctica bloom dynamics using remote sensing data for temperature, light, and chlorophyll a. Furthermore modeling based on the biophysical variables a*ph (), and  that are shown to regulate the growth rate provides a more fundamental mechanistic approach compared to other modeling methods that do not explicitly resolve photon flux into the cell or the quantum yield.

Highlights

The colonial prymnesiophyte Phaeocystis can dominate coastal, ice edge, and open ocean blooms in polar and temperate waters with significant implications for carbon export (Smith et al, 1991; DiTullio et al, 2000; van Leeuwe et al, 2007; Pavlov et al, 2017)
The light, temperature, and nutrient- dependence of phytoplankton growth has been well-characterized for a variety of species under a wide range of experimentally controlled laboratory conditions providing the basis for generalized models of phytoplankton growth for temperature, nutrients, and light limitation
Often these regulate growth in an interactive co-limitation matrix (Sosik and Mitchell, 1994; Sunda and Huntsman, 1997, 2011) there is lacking a mechanistic framework for modeling phytoplankton growth rate based on the biophysical variables of cellular absorption and quantum yield under simultaneous co-limitation

Summary

Introduction

The colonial prymnesiophyte Phaeocystis can dominate coastal, ice edge, and open ocean blooms in polar and temperate waters with significant implications for carbon export (Smith et al, 1991; DiTullio et al, 2000; van Leeuwe et al, 2007; Pavlov et al, 2017). We model steadystate growth based on the mechanistic biophysical parameters of chl-a specific spectral absorption and photosynthetic quantum yeield (a∗ph (λ) and φμ,) which are directly regulated by light, temperature, and nutrients (Kiefer and Mitchell, 1983; Sakshaug et al, 1989; Cullen, 1990; Moisan and Mitchell, 1999).

Results

Conclusion