Curvature in models of the photosynthesis‐irradiance response

Abstract

An equation for the rate of photosynthesis as a function of irradiance introduced by T. T. Bannister included an empirical parameter b to account for observed variations in curvature between the initial slope and the maximum rate of photosynthesis. Yet researchers have generally favored equations with fixed curvature, possibly because b was viewed as having no physiological meaning. We developed an analytic photosynthesis-irradiance equation relating variations in curvature to changes in the degree of connectivity between photosystems, and also considered a recently published alternative, based on changes in the size of the plastoquinone pool. When fitted to a set of 185 observed photosynthesisirradiance curves, it was found that the Bannister equation provided the best fit more frequently compared to either of the analytic equations. While Bannister's curvature parameter engendered negligible improvement in the statistical fit to the study data, we argued that the parameter is nevertheless quite useful because it allows for consistent estimates of initial slope and saturation irradiance for observations exhibiting a range of curvatures, which would otherwise have to be fitted to different fixed-curvature equations. Using theoretical models, we also found that intra-and intercellular self-shading can result in biased estimates of both curvature and the saturation irradiance parameter. We concluded that Bannister's is the best currently available equation accounting for variations in curvature precisely because it does not assign inappropriate physiological meaning to its curvature parameter, and we proposed that b should be thought of as the expression of the integration of all factors impacting curvature.Key index words: connectivity; curvature; models of photosynthetic rate versus irradiance; pigment packaging; saturation irradiance Abbreviations: ETC, electron transport chain; PQ, photosynthetic quotient; PSU, photosynthetic unit; PUR, photosynthetically utilizable irradiance; WNS, Webb, Newton, and StarrThe aquatic food web is based on the conversion of inorganic carbon into organic compounds by photosynthetic organisms, including benthic microalgae, macroalgae, seagrasses, and phytoplankton. While the focus here is on phytoplankton, in part because of the relative simplicity of the optical fields that can be assumed for dilute samples of photosynthetic microbes, our findings are based on generally applicable principles and have some relevance to all photosynthetic systems.Like all photosynthetic organisms, phytoplankton depends on light and nutrients for growth. Accurate estimation of the productive potential of an assemblage of phytoplankton is predicated on accurate quantification of the efficiency with which these resources are utilized, and can be crucial in the assessment of the structure and functioning of an aquatic ecosystem, estimation of the rate of carbon sequestration in climate models, and determination of the commercial feasibility of algal culture for the production of fuel, protein or other ...

Growth, Chl a content, photosynthesis, and elemental composition in polar and temperate microalgae

“…This is an important result because it shows that light limited photosynthesis is not significantly affected by temperature in polar species. These results must be interpreted with caution because data are scarce, protocols are numerous (i.e., different light sources) and values of α * are estimated by different models, which can lead to significant differences (Frenette ; Jones et al ).…”

Photosynthetic light requirements and vertical distribution of macroalgae in newly ice-free areas in Potter Cove, South Shetland Islands, Antarctica

“…The Webb equation is ubiquitous in the literature, probably because it is mathematically convenient and generally fits observations well. Jassby and Platt (1976) found that their hyperbolic tangent equation provided the best overall fit to close to 200 observed curves in a comparison of various equations (Jassby and Platt 1976;Jones et al 2014). Nevertheless, recent studies performed by Jones et al (2014) recommend that Bannister's model (Bannister 1979) is the most appropriate of existing P-I curve equations.…”

“…Jassby and Platt (1976) found that their hyperbolic tangent equation provided the best overall fit to close to 200 observed curves in a comparison of various equations (Jassby and Platt 1976;Jones et al 2014). Nevertheless, recent studies performed by Jones et al (2014) recommend that Bannister's model (Bannister 1979) is the most appropriate of existing P-I curve equations. This single model with variable curvature could solve the problem of P-I models with fixed curvatures that although they fit observations well they are not always comparable (Frenette et al 1993).…”

“…Lower case letters significant differences for P. decipiens among areas, and capital letters for significant differences for H. grandifolius between areas and depths Polar Biol (2016) 39:153-166 163 experimental data (Nelson and Siegrist 1987;Saba et al 2010;Jones et al 2014). In our study and for our data sets, Model 1 (hyperbolic tangent, Jassby and Platt 1976) was better suited than model 2 (exponential, Webb et al 1974) to explain our data because it had a better overall fit, highest AIC and precision in photosynthetic estimates.…”

“…Mathematical models relating light irradiance to photosynthesis are usually used to estimate primary productivity (Jassby and Platt 1976;Nelson and Siegrist 1987;Henley 1993, Jones et al 2014. However, the values of the obtained photosynthetic parameters may differ depending on the selected fitting model (Smith 1936;Steele 1962;Webb et al 1974;Jassby and Platt 1976;Cullen 1990;Frenette et al 1993;Henley 1993).…”