Abstract
Trichodesmium is a globally important marine diazotroph that accounts for approximately 60 − 80% of marine biological N2 fixation and as such plays a key role in marine N and C cycles. We undertook a comprehensive assessment of how the growth rate of Trichodesmium erythraeum IMS101 was directly affected by the combined interactions of temperature, pCO2 and light intensity. Our key findings were: low pCO2 affected the lower temperature tolerance limit (Tmin) but had no effect on the optimum temperature (Topt) at which growth was maximal or the maximum temperature tolerance limit (Tmax); low pCO2 had a greater effect on the thermal niche width than low-light; the effect of pCO2 on growth rate was more pronounced at suboptimal temperatures than at supraoptimal temperatures; temperature and light had a stronger effect on the photosynthetic efficiency (Fv/Fm) than did CO2; and at Topt, the maximum growth rate increased with increasing CO2, but the initial slope of the growth-irradiance curve was not affected by CO2. In the context of environmental change, our results suggest that the (i) nutrient replete growth rate of Trichodesmium IMS101 would have been severely limited by low pCO2 at the last glacial maximum (LGM), (ii) future increases in pCO2 will increase growth rates in areas where temperature ranges between Tmin to Topt, but will have negligible effect at temperatures between Topt and Tmax, (iii) areal increase of warm surface waters (> 18°C) has allowed the geographic range to increase significantly from the LGM to present and that the range will continue to expand to higher latitudes with continued warming, but (iv) continued global warming may exclude Trichodesmium spp. from some tropical regions by 2100 where temperature exceeds Topt.
Highlights
The ocean is a major sink for anthropogenic emissions [1], of which the capacity to store CO2 is strongly affected by biological processes [2]
The growth-light and growth-temperature curve fits for each CO2 or light treatment were fitted using a weighted non-linear squares algorithm, where weights were the reciprocals of the standard errors associated with the median growth rates
The growth responses were non-symmetrical around the optimum temperature for growth (Topt ranging between 24.7 to 26.9 ̊C); the effect of pCO2 on growth was more pronounced at suboptimal than supraoptimal temperatures (Fig 1A and 1B)
Summary
The Interacting Effects of Temperature, CO2 and Light on the Growth of Trichodesmium erythraeum IMS101. OPEN ACCESS Citation: Boatman TG, Lawson T, Geider RJ (2017) A Key Marine Diazotroph in a Changing Ocean: The Interacting Effects of Temperature, CO2 and Light on the Growth of Trichodesmium erythraeum IMS101.
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