Ocean Acidification

Highlights

• Effects of light availability and pCO₂ on Kappaphycus alvarezii were examined.
• Moderate increases in light intensity and pCO₂ had positive effects on K. alvarezii.
• OA and high light promoted carbon accumulation, but they had negative impacts on nitrogen.

Abstract

The concentration of atmospheric carbon dioxide (CO₂) has increased drastically over the past several decades, resulting in the pH of the ocean decreasing by 0.44 ± 0.005 units, known as ocean acidification (OA). The Kappaphycus alvarezii (Rhodophyta, Solieriaceae), is a commercially and ecologically important red macroalga with significant CO₂ absorption potential from seawater. The K. alvarezii also experienced light variations from self-shading and varied cultivation depths. Thus, the aim of present study was to investigate the effects of two pCO₂ levels (450 and 1200 ppmv) and three light intensities (50, 100, and 150 μmol photons·m⁻²·s⁻¹) on photosynthesis and the biochemical components in K. alvarezii. The results of the present study showed that a light intensity of 50 μmol photons·m⁻²·s⁻¹ was optimal for K. alvarezii photosynthesis with 0.663 ± 0.030 of F_v/F_m and 0.672 ± 0.025 of F_v’/F_m’. Phycoerythrin contents at two pCO₂ levels decreased significantly with an increase in light intensity by 57.14–87.76%, while phycocyanin contents only decreased from 0.0069 ± 0.001 mg g⁻¹ FW to 0.0047 ± 0.001 mg g⁻¹ FW with an increase in light intensity at 1200 ppmv of pCO₂. Moreover, moderate increases in light intensity and pCO₂ had certain positive effects on the physiological performance of K. alvarezii, specifically in terms of increasing soluble carbohydrate production. Although OA and high light levels promoted total organic carbon accumulation (21.730 ± 0.205% DW) in K. alvarezii, they had a negative impact on total nitrogen accumulation (0.600 ± 0.017% DW).

Zhang Y., Xiao Z., Wei Z. & Long L., 2024. Increased light intensity enhances photosynthesis and biochemical components of red macroalga of commercial importance, Kappaphycus alvarezii, in response to ocean acidification. Plant Physiology and Biochemistry 208: 108465. doi: 10.1016/j.plaphy.2024.108465. Article.