Functional macrophyte trait variation as a response to the source of inorganic carbon acquisition

Background This study aims to compare variation in a range of aquatic macrophyte species leaf traits into three carbon acquisition groups: HCO3−, free CO2 and atmospheric CO2. Methods The leaf functional traits were measured for 30 species from 30 softwater lakes. Macrophyte species were classified into (1) free CO2, (2) atmospheric CO2 and (3) bicarbonate HCO3− groups. In each lake we collected water samples and measured eight environmental variables: depth, Secchi depth, photosynthetically active radiation (PAR), pH of water, conductivity, calcium concentration, total nitrogen and total phosphorus. In this study we applied the RLQ analysis to investigate the relationships between species functional traits (Q) and their relationship with environmental variables (R) constrained by species abundance (L). Results The results showed that: (1) Aquatic macrophytes exhibited high leaf trait variations as a response to different inorganic carbon acquisition; (2) Traits of leaves refer to the acquisition of carbon for photosynthesis and serve to maximise this process; (3) In the wide softwater habitat, macrophyte species exhibited an extreme range of leaf economic spectrum (leaf area, leaf dry weight and specific leaf area) and wide range of shape trait expressed as circularity; (4) Macrophyte leaf traits are the result of adaptation to carbon acquisition in ambient environment.

Regulation of inorganic carbon acquisition in a red tide alga (<i>Skeletonema costatum</i>): the importance of phosphorus availability

Skeletonema costatum is a common bloom-forming diatom and encounters eutrophication and severe carbon dioxide (CO2) limitation during red tides. However, little is known regarding the role of phosphorus (P) in modulating inorganic carbon acquisition in S. costatum, particularly under CO2 limitation conditions. We cultured S. costatum under five phosphate levels (0.05, 0.25, 1, 4, 10 µmol L−1) and then treated it with two CO2 conditions (2.8 and 12.6 µmol L−1) for 2 h. The lower CO2 reduced net photosynthetic rate at lower phosphate levels (< 4 µmol L−1) but did not affect it at higher phosphate levels (4 and 10 µmol L−1). In contrast, the lower CO2 induced a higher dark respiration rate at lower phosphate levels (0.05 and 0.25 µmol L−1) and did not affect it at higher phosphate levels (> 1 µmol L−1). The lower CO2 did not change relative electron transport rate (rETR) at lower phosphate levels (0.05 and 0.25 µmol L−1) and increased it at higher phosphate levels (> 1 µmol L−1). Photosynthetic CO2 affinity (1/K0.5) increased with phosphate levels. The lower CO2 did not affect photosynthetic CO2 affinity at 0.05 µmol L−1 phosphate but enhanced it at the other phosphate levels. Activity of extracellular carbonic anhydrase was dramatically induced by the lower CO2 in phosphate-replete conditions (> 0.25 µmol L−1) and the same pattern also occurred for redox activity of the plasma membrane. Direct bicarbonate (HCO3-) use was induced when phosphate concentration was more than 1 µmol L−1. These findings indicate P enrichment could enhance inorganic carbon acquisition and thus maintain the photosynthesis rate in S. costatum grown under CO2-limiting conditions via increasing activity of extracellular carbonic anhydrase and facilitating direct HCO3- use. This study sheds light on how bloom-forming algae cope with carbon limitation during the development of red tides.

Regulation of inorganic carbon acquisition in a red tide alga (<i>Skeletonema costatum</i>): the importance of phosphorus availability

S. costatum is a common bloom-forming diatom and encounters eutrophication and severe CO2 limitation during red tides. However, little is known regarding the role of phosphorus in modulating inorganic carbon acquisition in S. costatum，particularly under CO2 limitation conditions. We cultured S. costatum under five phosphate levels (0.05, 0.25, 1, 4, 10 μmol L−1) and then treated it with two CO2 conditions (2.8 and 12.6 μmol L−1) for two hours. The lower CO2 reduced net photosynthetic rate at lower phosphate levels ( 1 μmol L−1). The lower CO2 did not change rETR at lower phosphate levels (0.05 and 0.25 μmol L−1) and increased it at higher phosphate levels (> 1 μmol L−1). Photosynthetic CO2 affinity (K0.5) decreased with phosphate levels. The lower CO2 did not affect K0.5 at 0.05 μmol L−1 phosphate but reduced it at the other phosphate levels. Activity of extracellular carbonic anhydrase was dramatically induced by the lower CO2 at phosphate replete conditions (> 0.25 μmol L−1) and the same pattern also occurred for redox activity of plasma membrane. Direct HCO3− use was induced when phosphate concentration is more than 1 μmol L−1. This study indicates the essential role of P in regulating inorganic carbon acquisition and CO2 concentrating mechanisms (CCMs) in S. costatum and sheds light on how bloom-forming algae cope with carbon limitation during the development of red tides.