Articles | Volume 14, issue 3
Biogeosciences, 14, 671–681, 2017
https://doi.org/10.5194/bg-14-671-2017
Biogeosciences, 14, 671–681, 2017
https://doi.org/10.5194/bg-14-671-2017

Research article 10 Feb 2017

Research article | 10 Feb 2017

Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification and phosphorus enrichment

Zhiguang Xu1,2, Guang Gao1,3, Juntian Xu1, and Hongyan Wu4 Zhiguang Xu et al.
  • 1Marine Resources Development Institute of Jiangsu, Huaihai Institute of Technology, Lianyungang 222005, China
  • 2Marine Biology Institute of Shandong Province, Qingdao 266104, China
  • 3School of Marine Science and Technology, Ridley Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
  • 4Hubei University of Technology, Wuhan 430068, China

Abstract. The development of golden tides is potentially influenced by global change factors, such as ocean acidification and eutrophication, but related studies are very scarce. In this study, we cultured a golden tide alga, Sargasssum muticum, at two levels of pCO2 (400 and 1000 µatm) and phosphate (0.5 and 40 µM) to investigate the interactive effects of elevated pCO2 and phosphate on the physiological properties of the thalli. Higher pCO2 and phosphate (P) levels alone increased the relative growth rate by 41 and 48 %, the net photosynthetic rate by 46 and 55 %, and the soluble carbohydrates by 33 and 62 %, respectively, while the combination of these two levels did not promote growth or soluble carbohydrates further. The higher levels of pCO2 and P alone also enhanced the nitrate uptake rate by 68 and 36 %, the nitrate reductase activity (NRA) by 89 and 39 %, and the soluble protein by 19 and 15 %, respectively. The nitrate uptake rate and soluble protein was further enhanced, although the nitrate reductase activity was reduced when the higher levels of pCO2 and P worked together. The higher pCO2 and higher P levels alone did not affect the dark respiration rate of the thalli, but together they increased it by 32 % compared to the condition of lower pCO2 and lower P. The neutral effect of the higher levels of pCO2 and higher P on growth and soluble carbohydrates, combined with the promoting effect on soluble protein and dark respiration, suggests that more energy was drawn from carbon assimilation to nitrogen assimilation under conditions of higher pCO2 and higher P; this is most likely to act against the higher pCO2 that caused acid–base perturbation via synthesizing H+ transport-related protein. Our results indicate that ocean acidification and eutrophication may not boost golden tide events synergistically, although each one has a promoting effect.

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Higher levels of CO2 and phosphate increased the relative growth rate, nitrate uptake rate, soluble carbohydrates, and soluble protein in a golden tide alga (Sargassum muticum), but the combination of these two levels did not promote growth further. Our results indicate that ocean acidification and eutrophication may not boost golden tide events synergistically, although each one has a promoting effect.
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