Table 1.

Net photosynthetic rates of the diatom Thalassiosira weissflogii grown and measured under four pO₂/pCO₂ conditions with and without the extracellular (periplasmic) carbonic anhydrase inhibitor acetazolamide (AZ).

		-AZ	+ AZ	Inhibition
		(fmol O2 cell−1 min−1)	(fmol O2 cell−1 min−1)	(%)
AC	AO	41 ± 2.9b	36 ± 2.3cd	11 ± 1.6b
	LO	45 ± 3.5b	37 ± 2.6c	18 ± 2.1a
HC	AO	43 ± 2.7b	44 ± 3.0b	None
	LO	55 ± 2.1a	56 ± 2.3a	None

Values represent means ± standard deviation (n = 3) for replicate cultures under ambient (AO, ~255 μM) and low O₂ levels (LO, ~57 μM) with ambient (AC, ~15 μM) and elevated CO₂ levels (HC, ~35 μM), and different letters (superscripted) represent significant differences (P < 0.05, LSD test) among +AZ and −AZ treatments. Photosynthetic inhibition in high CO₂-grown cells was not detected (none), while low O₂-grown cells showed the highest photosynthetic inhibition. The detailed information for the experimental features and timing points are shown in Supplementary Fig. 3.