Table 3.
Net C fixation, net CO2 uptake, HCO3− uptake, eCA activity and leakage of Scrippsiella trochoidea and Alexandrium tamarense in the different CO2 treatments. Values for Vmax and K1/2 are given in µmol mg−1 Chl a h−1 and µmol l−1, respectively. A dash indicates that values could not be determined. If not stated otherwise, values represent the mean ± sd of triplicate incubations (n = 3). A significant difference between treatments is denoted by different letters
| pCO2 (µatm) | Net C fixation | Net CO2 uptake | HCO3− uptake | eCA activity U (µg−1 Chl a) | Leakage CO2 efflux: total Ci uptake | ||||
|---|---|---|---|---|---|---|---|---|---|
| Vmax | K1/2 (CO2) | K1/2 (DIC) | Vmax | K1/2 (CO2) | Vmax | K1/2 (HCO3−) | |||
| S. trochoidea | |||||||||
| 180 | 199 ± 41 | 3.8 ± 0.5 | 94 ± 50 | −13 ± 37a | – | 194 ± 5 | 7.2 ± 12.4 | 1573 ± 108 | 0.56 ± 0.06 |
| 380 | 239 ± 62 | 4.7 ± 1.1 | 160 ± 40 | −7 ± 29a | – | 225 ± 40 | 17 ± 1.4 | 1416 ± 22 | 0.53 ± 0.06 |
| 800 | 246 ± 62 | 5.5 ± 0.9 | 263 ± 51 | −3 ± 40ab | – | 202 ± 32 | 3.7 ± 5.5 | 1232 ± 144 | 0.54 ± 0.01 |
| 1200 | 239 ± 38 | 5.1 ± 0.4 | 269 ± 78 | 89 ± 22b | 20.1 ± 0.6 | 165 ± 26 | 10.3 ± 17 | 1301 ± 99 | 0.48 ± 0.04 |
| A. tamarense | |||||||||
| 180 | 101 ± 2a | 2.4 ± 0.1 | 267 ± 43 | 66 ± 9a | 3.3 ± 0.2 | 36 ± 5 | 105 ± 45 | 19 ± 48 (n = 2) | 0.44 ± 0.01a |
| 380 | 101 ± 14ab | 2.8 ± 0.2 | 309 ± 67 | 60 ± 16ab | 3.3 ± 0.3 | 38 ± 7 | 220 ± 96 | 86 ± 2 (n = 2) | 0.46 ± 0.02a |
| 800 | 83 ± 7ab | 2.0 ± 0.9 | 206 ± 65 | 42 ± 8ab | 3.1 ± 1.0 | 42 ± 10 | 158 ± 143 | 156 ± 12 (n = 2) | 0.53 ± 0.02b |
| 1200 | 61 ± 8c | 2.5 ± 0.2 | 173 ± 15 | 23 ± 26b | 4.5 ± 0.8 | 38 ± 13 | 148 ± 28 | 124 (n = 1) | 0.63 ± 0.05c |