Effecets Of Increased Carbon Dioxide On Nutrient Metabolites In Kelp

As an important food source for some segments of human population,kelps rich in calcium,iron,sodium,magnesium,linoleic acid and lecithin.Meanwhile,as an impormant primary producer of the ocean,kelps provides critical services for coastal food chains and ecosystem.With the intensification of human production activities and the change of global climate,the carbon dioxide continues increases,it caused greenhouse effect and global warming.However,ocean as the natural storage of carbon dioxide,it absorbs about 30% of human carbon dioxide emissions.Despite their ecological importance,little is known about long-term impacts of elevated CO₂（eCO₂） on nutrient metabolites in kelps.In this study,the kelp Saccharina japonica was cultured in CO₂ enriched coastal mesocosm systems for up to 3 months.We found that:（1）eCO₂ significantly increased the growth rate of S.japonica,the average blade length,width and weight under eCO₂ were 49.9%,40.3% and 70.1% higher relative to the controls,respectively.（2）eCO₂ significantly increased kelps carbon concentrations and C/N ratio of S.japonica,C content were 8.5% higher relative to the controls.（3）Elevated CO₂ had a significantly negative effect on lipid content.Lipid content decreased by 26.7% and 18.8%after cultivation for 2 and 3 months under eCO₂,respectively,but there was no significant effect of eCO₂ on the ω6/ω3 ratio compared to the control.（4）The phosphorus and potassium contents were significantly increased in eCO₂ by 14.11% and 14.09% respectively after 3-month cultivation,but it had no statistically significant effect on zinc or iron contents,on the contrary,eCO₂ significantly decreased contents of magnesium,sodium and calcium by 12.6%,18.7% and 16.4%,respectively after 3-month cultivation and lowered sodium content by 11.7% after 2 months.