Effects of elevated pCO2 and nutrient enrichment on the growth, photosynthesis, and biochemical compositions of the brown alga Saccharina japonica (Laminariaceae, Phaeophyta).

Yaoyao Chu,Jingyu Li,Qingli Gong,Yan Liu

doi:10.7717/peerj.8040

Abstract

Ocean acidification and eutrophication are two major environmental issues affecting kelp mariculture. In this study, the growth, photosynthesis, and biochemical compositions of adult sporophytes of Saccharina japonica were evaluated at different levels of pCO2 (400 and 800 µatm) and nutrients (nutrient-enriched and non-enriched seawater). The relative growth rate (RGR), net photosynthetic rate, and all tested biochemical contents (including chlorophyll (Chl) a, Chl c, soluble carbohydrates, and soluble proteins) were significantly lower at 800 µatm than at 400 µatm pCO2. The RGR and the contents of Chl a and soluble proteins were significantly higher under nutrient-enriched conditions than under non-enriched conditions. Moreover, the negative effects of the elevated pCO2 level on the RGR, net photosynthetic rate, Chl c and the soluble carbohydrates and proteins contents were synergized by the elevated nutrient availability. These results implied that increased pCO2could suppress the growth and biochemical composition of adult sporophytes of S. japonica. The interactive effects of ocean acidification and eutrophication constitute a great threat to the cultivation of S. japonica due to growth inhibition and a reduction in quality.

Highlights

Due to intensive anthropogenic activities in recent years, the level of CO2 in the atmosphere has increased from 285 μatm in 1975 to >400 μatm at present (IPCC, 2014)
The discs were stock-cultured in a plastic tank containing 6 L filtered seawater, which was obtained from the coast of Taipingjiao, Qingdao with a salinity of approximately 30 psu
The two-way analysis of variance (ANOVA) (p = 0.05) showed that pCO2 had a significant effect on all parameters except for Total alkalinity (TA), whereas the nutrient level did not have a significant influence on any parameter

Summary

Introduction

Due to intensive anthropogenic activities in recent years, the level of CO2 in the atmosphere has increased from 285 μatm in 1975 to >400 μatm at present (IPCC, 2014). This caused an increase in the concentration of dissolved CO2 in the ocean, resulting in a decrease in seawater pH, which is called ocean acidification (OA). Excessive nutrient inputs can lead to harmful algal blooms (Bricker et al, 2008; Cai et al, 2011; Smetacek & Zingone, 2013), which decrease oxygen concentrations in the water column and produce toxins that might be lethal to marine organisms, thereby resulting in shifts in species dominance and community structure (Glibert et al, 2005; Xiao et al, 2017)

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Results

Discussion

Conclusion