Interactions between Thermal Acclimation, Growth Rate, and Phylogeny Influence Prochlorococcus Elemental Stoichiometry

Abstract

Variability in plankton elemental requirements can be important for global ocean biogeochemistry but we currently have a limited understanding of how ocean temperature influences the plankton C/N/P ratio. Multiple studies have put forward a ‘translation-compensation’ hypothesis to describe the positive relationship between temperature and plankton N/P or C/P as cells should have lower demand for P-rich ribosomes and associated depressed QP when growing at higher temperature. However, temperature affects many cellular processes beyond translation with unknown outcomes on cellular elemental composition. In addition, the impact of temperature on growth and elemental composition of phytoplankton is likely modulated by the life history and growth rate of the organism. To test the direct and indirect (via growth rate changes) effect of temperature, we here analyzed the elemental composition and ratios in six strains affiliated with the globally abundant marine Cyanobacteria Prochlorococcus. We found that temperature had a significant positive effect on the carbon and nitrogen cell quota, whereas no clear trend was observed for the phosphorus cell quota. The effect on N/P and C/P were marginally significantly positive across Prochlorococcus. The elemental composition and ratios of individual strains were also affected but we found complex interactions between the strain identity, temperature, and growth rate in controlling the individual elemental ratios in Prochlorococcus and no common trends emerged. Thus, the observations presented here does not support the ‘translation-compensation’ theory and instead suggest unique cellular elemental effects as a result of rising temperature among closely related phytoplankton lineages. Thus, the biodiversity context should be considered when predicting future elemental ratios and how cycles of carbon, nitrogen, and phosphorus may change in a future ocean.

The cobalt cycle in the Tropical Pacific Ocean

“…Agreement between cellular P quotas (1.1 ± 0.4 x 10 7 atoms per cell) and literature data for this strain (0.4-0.7 x 10 7 atoms per cell (Martiny et al, 2016)) and Prochlorococcus Med4 (0.2-2 x 10 7 atoms per cell, (Bertilsson et al, 2003)) indicate that ICPMS and flow cytometry determinations are robust. The 1.7 M bp genome of Prochlorococcus MIT9215 alone accounts for 0.3 x 10 7 P atoms per cell, a considerable fraction of the cellular P quota.…”

Phytoplankton as Key Mediators of the Biological Carbon Pump: Their Responses to a Changing Climate

“…They attributed the observed rise in algal N:P and C:P ratios, with rising temperatures, to decline in cellular quotas of P-rich assembly machinery (ribosomes), relative to N-rich light harvesting machinery (chloroplasts and proteins), with increasing temperature. On the contrary, Martiny et al [65], showed that thermal effect leads to increased cellular quotas of nitrogen and carbon, whereas the cellular phosphorous quota changes very little in the marine cyanobacterium, Prochlorococcus. Their results point towards other physiological acclimation mechanisms as the principal drivers of elemental changes in Prochlorococcus.…”

Functional Genomics Differentiate Inherent and Environmentally Influenced Traits in Dinoflagellate and Diatom Communities

“…Temperature has been shown to positively correlate with C:P and N:P ratios, but not with C:N. These shifts occur because fewer P-rich ribosomes are required at warmer temperatures due to their increased use efficiency [62,63,67,68]. However, elevated C and N content and a decrease of P have also been attributed to observed stoichiometric changes in warm-acclimated phytoplankton cells [69]. Hence, more than one process potentially causes temperature-dependent shifts in elemental ratios.…”