Regulation of inorganic carbon acquisition in a red tide alga (<i>Skeletonema costatum</i>): the importance of phosphorus availability
<p><i>Skeletonema costatum</i> is a common bloom-forming diatom and encounters eutrophication and severe carbon dioxide (CO<sub>2</sub>) limitation during red tides. However, little is known regarding the role of phosphorus (P) in modulating inorganic carbon acquisit...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-08-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/4871/2018/bg-15-4871-2018.pdf |
| Summary: | <p><i>Skeletonema costatum</i> is a common bloom-forming diatom and encounters
eutrophication and severe carbon dioxide (CO<sub>2</sub>) limitation during red
tides. However, little is known regarding the role of phosphorus (P) in
modulating inorganic carbon acquisition in <i>S. costatum</i>, particularly
under CO<sub>2</sub> limitation conditions. We cultured <i>S. costatum</i> under
five phosphate levels (0.05, 0.25, 1, 4, 10 µmol L<sup>−1</sup>) and then
treated it with two CO<sub>2</sub> conditions (2.8 and 12.6 µmol L<sup>−1</sup>)
for 2 h. The lower CO<sub>2</sub> reduced net photosynthetic rate at lower
phosphate levels (< 4 µmol L<sup>−1</sup>) but did not affect it at
higher phosphate levels (4 and 10 µmol L<sup>−1</sup>). In contrast, the lower
CO<sub>2</sub> induced a higher dark respiration rate at lower phosphate levels (0.05
and 0.25 µmol L<sup>−1</sup>) and did not affect it at higher phosphate levels
(> 1 µmol L<sup>−1</sup>). The lower CO<sub>2</sub> did not change
relative electron transport rate (rETR) at lower phosphate levels (0.05 and
0.25 µmol L<sup>−1</sup>) and increased it at higher phosphate levels
(> 1 µmol L<sup>−1</sup>). Photosynthetic CO<sub>2</sub> affinity
(1/<i>K</i><sub>0.5</sub>) increased with phosphate levels. The lower CO<sub>2</sub> did not
affect photosynthetic CO<sub>2</sub> affinity at 0.05 µmol L<sup>−1</sup> phosphate but enhanced it at the other phosphate levels. Activity of
extracellular carbonic anhydrase was dramatically induced by the lower
CO<sub>2</sub> in phosphate-replete conditions (> 0.25 µmol L<sup>−1</sup>) and the same pattern also occurred for redox activity of the plasma
membrane. Direct bicarbonate (HCO<sub>3</sub><sup>−</sup>) use was induced when phosphate
concentration was more than 1 µmol L<sup>−1</sup>. These findings indicate P
enrichment could enhance inorganic carbon acquisition and thus maintain the
photosynthesis rate in <i>S. costatum</i> grown under CO<sub>2</sub>-limiting
conditions via increasing activity of extracellular carbonic anhydrase and
facilitating direct HCO<sub>3</sub><sup>−</sup> use. This study sheds light on how
bloom-forming algae cope with carbon limitation during the development of red
tides.</p> |
|---|---|
| ISSN: | 1726-4170 1726-4189 |