Figure 1.
Effect of increasing CO2 concentrations on growth and calcification.
(A) Specific growth rate, (B) PIC and POC, (C) PIC:POC ratio, and (D) fraction of completed cysts. Solid lines indicate linear regressions (n = 12) with (A) R2 = 0.94, P<0.001, (B) POC: R2 = 0.35, P = 0.042, and PIC: R2 = 0.66, P = 0.001, (C) R2 = 0.70, P<0.001, and (D) R2 = 0.98, P<0.001.
Figure 2.
Effect of elevated pCO2 on cyst morphology.
Cells grown under (A–C) 150 µatm CO2 and (D–H) 1400 µatm CO2. Black arrows indicate cysts that are shown in detailed images, white arrows show collapsed cysts.
Figure 3.
Effect of increasing CO2 concentrations on the stable isotope composition.
(A) 13C fractionation of organic carbon (εp) and calcite (εk), (B) 18O composition of calcite (δ18Ocalcite) and DIC (δ18ODIC), and (C) relationship between the oxygen isotopic composition of calcite (δ18Ocalcite-water) in Thoracosphaera from this study (open diamonds) and from Ziveri et al. [9] (grey diamonds). Horizontal lines in (B) indicate δ18O values for HCO3− and CO32−, and dashed line indicates trend of curve. Solid lines indicate linear regressions (n = 12) with (A) εp: R2 = 0.75, P<0.001, and εk: R2 = 0.90, P<0.001, (B) δ18ODIC: R2 = 0.76, P<0.001, and (C) This study: R2 = 0.99, P<0.001, and Ziveri et al. (2012), (n = 7): R2 = 0.95, P<0.001.
Figure 4.
Effect of elevated pCO2 on gene regulation.
Number of readings found for genes associated to ion transport and Ci acquisition in the 150 µatm and 1400 µatm CO2 treatments relative to the present-day (380 µatm) CO2 treatment.
Figure 5.
Conceptual model of regulated proteins in a T. heimii cell.
The regulated proteins involved in ion transport and Ci acquisition are shown on their putative locations [39], [49], [57]. Proteins involved in vacuolar Ca2+ and H+ transport include P-type Ca2+ ATPases (P-ATPase), Ca2+/Na+ exchangers (NCX), Ca2+/H+ antiporters (VCX), and vacuolar H+ ATPases (V-ATPase). Active uptake of HCO3− may occur via a SLC4 family anion exchanger (AE) or an SLC26 family SO43−/HCO3−/C2O42− anion exchanger (SAT-1). Carbonic anhydrases (CA) are located intracellularly or extracellularly and enhance the interconversion between CO2 and HCO3−.