An Integrated Response of Trichodesmium erythraeum IMS101 Growth and Photo-Physiology to Iron, CO2, and Light Intensity

Abstract

We have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m−2 s−1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe′) concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe′ concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.

Inorganic carbon and pH dependency of photosynthetic rates in Trichodesmium

“…The increased growth rates that we observed from low- (180 µmol mol –1 ) to mid- (380 µmol mol –1 ) and high-CO 2 treatments (720 µmol mol –1 ) were similar to previous findings ( Barcelos e Ramos et al , 2007 ; Boatman et al , 2017 , 2018 b ). The growth rate at high CO 2 was 8% greater than at mid-CO 2 , but this difference was not statistically significant.…”

“…The growth rates reported here were comparable to the 2-µM EDTA, iron-replete (unchelated) treatments in Boatman et al (2017) , as well as 20-µM EDTA, iron-replete (chelated) cultures ( Boatman et al , 2018 b ), which suggests that our cultures were not exposed to toxic concentrations of certain trace metals (e.g. copper) caused from low trace metal buffering capacity, as reported by Hong et al (2017) .…”

Projected expansion of Trichodesmium’s geographical distribution and increase in growth potential in response to climate change

“…The data groupings consisted of: (a) combined low/mid CO 2 , (b) combined low/high CO 2 , (c) combined mid/ high CO 2 and (d) all CO 2 data combined. Note, as previous studies have shown that Trichodesmium's maximum growth rate (µ max ) is significantly reduced at low CO 2 relative to mid CO 2 , and is consistently ~10% higher from mid to high CO 2 (Boatman, Davey, Lawson, & Geider, 2018;Boatman et al, 2017;Boatman, Mangan, Lawson, & Geider, 2018;Boatman, Oxborough, et al, 2018), ′ max was maintained independent between CO 2 conditions. Having processed all model iterations by optimizing all parameter groupings, maximum likelihood (L) values were calculated using each model's residual sum of squares and the number of data points (n = 184).…”

“…Trichodesmium's fundamental niche will be principally determined by the direct physiological relationship between abundance and SST. Other research suggests that CO 2 concentrations projected for the end of this century (~720/750 ppm CO 2 ) could enhance rates of photosynthesis, nitrogen fixation and growth of Trichodesmium (Barcelos e Ramos, Biswas, Schulz, Laroche, & Riebesell, 2007;Boatman, Lawson, & Geider, 2017;Boatman, Oxborough, Gledhill, Lawson, & Geider, 2018;Hutchins et al, 2007;Levitan et al, 2007).…”

“…A more detailed description of the laboratory methodology, culturing technique and analytical procedure is reported in our previous studies (Boatman et al, 2017;Boatman, Oxborough, et al, 2018).…”