Abstract
The responses of macroalgae to ocean acidification could be altered by availability of macronutrients, such as ammonium (NH4+). This study determined how the opportunistic macroalga, Ulva australis responded to simultaneous changes in decreasing pH and NH4+ enrichment. This was investigated in a week-long growth experiment across a range of predicted future pHs with ambient and enriched NH4+ treatments followed by measurements of relative growth rates (RGR), NH4+ uptake rates and pools, total chlorophyll, and tissue carbon and nitrogen content. Rapid light curves (RLCs) were used to measure the maximum relative electron transport rate (rETRmax) and maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm). Photosynthetic capacity was derived from the RLCs and included the efficiency of light harvesting (α), slope of photoinhibition (β), and the light saturation point (Ek). The results showed that NH4+ enrichment did not modify the effects of pH on RGRs, NH4+ uptake rates and pools, total chlorophyll, rETRmax, α, β, Fv/Fm, tissue C and N, and the C:N ratio. However, Ek was differentially affected by pH under different NH4+ treatments. Ek increased with decreasing pH in the ambient NH4+ treatment, but not in the enriched NH4+ treatment. NH4+ enrichment increased RGRs, NH4+ pools, total chlorophyll, rETRmax, α, β, Fv/Fm, and tissue N, and decreased NH4+ uptake rates and the C:N ratio. Decreased pH increased total chlorophyll content, rETRmax, Fv/Fm, and tissue N content, and decreased the C:N ratio. Therefore, the results indicate that U. australis growth is increased with NH4+ enrichment and not with decreasing pH. While decreasing pH influenced the carbon and nitrogen metabolisms of U. australis, it did not result in changes in growth.
Highlights
Since the industrial revolution, the atmospheric CO2 concentration has increased from 280 μatm to over 390 μatm, and about 30% of the additional CO2 has been absorbed by the ocean [1]
The growth, nutrient, and photosynthetic physiology of Ulva australis with increased pCO2/ decreased pH did not depend on the NH4+ treatment, with the exception of Ek
This was counter to the hypothesis that NH4+ enrichment and increased pCO2/decreased pH would interact to change U. australis growth and physiology
Summary
The atmospheric CO2 concentration has increased from 280 μatm to over 390 μatm, and about 30% of the additional CO2 has been absorbed by the ocean [1]. This results in ocean acidification, a term which describes the contemporary reduction in seawater pH by ca. Excess nitrogen is the commonly regarded cause for green algal blooms world-wide, and they are typically dominated by macroalgae from the genus Ulva [8,9,10]. In order to understand how nutrientopportunistic macroalgae, such as Ulva spp. will respond to future oceanic conditions, it is important to consider the interaction of elevated nutrients with decreasing pH
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
