Ocean Acidification

Highlights

• The ratio of Chl a/b is reduced by the interaction between CO₂ and NO₃-N.
• The interaction between CO₂ and NO₃-N reduces the soluble sugar contents in leaves.
• CO₂ promotes the content of soluble protein in leaves while reduces that in roots.
• CO₂ reduces both the SOD activities of the rhizomes and the eelgrass mortality rate.
• Eelgrass has complex carbon supply and conversion mechanisms to ensure its survival.

Abstract

Carbon deficiency in the eelgrass caused by nutrient eutrophication and high concentrations of sulfate causes eelgrass mortality; however, ocean acidification provides sufficient carbon. Thus, it is inferred that ocean acidification might reduce the carbon deficiency. To verify this hypothesis, eelgrass clonal ramets were exposed to 72—h combined conditions of ocean acidification (CO₂), nitrate (NO₃-N), ammonia (NH₄-N), phosphate (PO₄-P) and sulfate (SO₄-S). The pigment contents were affected by nutrients; however, the Chl a/b ratio was inhibited by the interaction between CO₂ and NO₃-N and was promoted by interaction between NO₃-N and NH₄-N. The soluble protein contents in leaves were increased by CO₂; however, the soluble protein contents in roots were reduced by CO₂. The soluble sugar contents in the leaves had negatively correlation with the interaction between NO₃-N and CO₂. Moreover, the SOD activities of the rhizomes were inhibited by CO₂. All these findings suggest that ocean acidification does not seem to effectively alleviate the deficiency of soluble carbon in eelgrass under eutrophication and high concentrations of sulfate; however, the eelgrass mortality rate was inhibited by CO₂ and the interaction between PO₄-P and SO₄-S. Thus, eelgrass has extremely complex carbon supply and conversion mechanisms to ensure its survival under composite conditions or eelgrass has another mechanism of death in eutrophication.

Tan Q., Yang Q., Zhang H., Gu W., He Q., Wang Y., Liu H. & Ge C., 2025. Can ocean acidification alleviate carbon deficiency in eelgrass Zostera marina clonal ramets under conditions of nutrients, sulfate and ocean acidification? Regional Studies in Marine Science 91: 104548. doi: 10.1016/j.rsma.2025.104548. Article (restricted access).