Carbon stable isotope discrimination during respiration in three seaweed species

Abstract

Very little is known about seaweed stable carbon isotope discrimination during respiration (Δ r , defined here as the difference between respired CO 2 δ 13 C and algal tissue δ 13 C). However, Δ r can give information on carbon metabolic pathways in seaweeds, and can also be helpful to better understand their role in carbon cycling. Here we measured the Δ r of Ulva sp. (Chlorophyta), Pterocladia capillacea Bornet (Rhodophyta) and Sargassum sp. (Ochrophyta) under 3 different experimental conditions: at 15 and 25°C after strong illumination for 30 to 60 min, and at 25°C after at least 20 h in the dark. We observed a correlation between Δ r and the respiratory quotient (RQ, defined as the ratio between CO 2 release and O 2 consumption), suggesting changes in the organic substrate used for respiration in the different treatments. Δ r was positive in most cases, suggesting that carbohydrates were the likely substrate for respiration; however, Δ r (and the RQ) decreased with an increase in temperature, suggesting increased use of lipids as substrates. Although Δ r was not large (averaging 3 ‰), the influence of seaweed respiration on the δ 13 C of dissolved inorganic carbon may need to be taken into account in ecosystems where seaweeds dominate primary production (i.e. eutrophic lagoons). Δ r may also be important when interpreting seaweed δ 13 C values to determine the form of inorganic carbon used in photosynthesis. KEY WORDS:13 C · Fractionation · Macroalgae · Respiration · Respiratory quotient · Short-term incubation Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 437: [41][42][43][44][45][46][47][48][49] 2011 the bulk algal tissue) influence on the overall organism δ 13 C can be important. Aquatic respiration is typically dominated by microbial respiration (Del Giorgio & Williams 2005), including respiration of seaweed detritus. However, respiration by seaweeds comprises the bulk of the respiration in some coastal communities (Middelburg et al. 2005), which means that CO 2 respired by seaweeds may influence the δ 13 C of dissolved inorganic carbon in nearby waters, especially in rocky tidal pools during low tide.In terrestrial plants, there has been a growing recognition that not only Δ p , but also Δ r , can shape plant δ 13 C (Ghashghaie et al. 2003, Pataki 2005, Tcherkez et al. 2010, although this has largely been ignored in aquatic plants. It is un known if the patterns found for Δ r in land plants are also observed in algae; thus, studies addressing Δ r could enhance understanding of the variation of δ 13 C in algae. Investigations in land plants have shown that temperature and light exposure affect Δ r (Tcherkez et al. 2003, Gessler et al. 2009, Werner et al. 2009). An increase in temperature can cause an increased rate of lipid consumption, which is reflected in Δ r (Tcherkez et al. 2003). Light exposure inhibits part of the Krebs cycle, leading to the accumulation of metabolites which are preferentially consumed in the first minutes of darkness,...

Light respiration by subtropical seaweeds

“…For both species, temperature clearly influenced OCR (Fig. ), as is often observed for aquatic organisms (Del Giorgio and Williams , Carvalho and Eyre , ). However, temperature did not clearly influenced light CRR (Fig.…”

“…Incubations were done following the procedures in Carvalho and Eyre (, ) with minor modifications. Briefly, pre‐acclimated thalli were transferred to the incubation chambers (transparent 80 mL plastic syringes with magnetic stir bars inside), and the incubation medium was added (filtered seawater and ~2% of extra 13 C; in one case, by mistake, only 0.3% was added, but this did not compromise the results because of the large change in dissolved inorganic carbon [DIC] concentrations in the incubations).…”

Climate change and ocean acidification effects on seagrasses and marine macroalgae

“…Seagrasses tend to have negative d 13 values reminiscent of C 4 photosynthesis. However, the photosynthetic use of both CO 2 and HCO 3 À , which differ in d 13 values, as well as enhanced recycling of CO 2 due to aqueous DIC diffusion restraints, make d 13 isotopic C signatures an unreliable indicator for C 4 photosynthesis in the aquatic environment, and thus C 4 predictions based on such data should be viewed with caution (Andrews & Abel, 1979;McMillan et al, 1980;Carvalho & Eyre, 2011). Among marine macroalgae reviewed (Table 1), the presence of a single-cell C 4 pathway has been documented in the tropical chlorophyte Udotea flabellum Reiskind & Bowes, 1991).…”

Carbon Isotopic Fractionation in Organic Matter Production Consistent With Benthic Community Composition Across a Coral Reef Flat

“…Photosynthetic preference for either CO 2 or HCO − 3 will also affect estimates of ǫ OM because of the equilibrium fractionation between CO 2 and HCO − 3 (ǫ CO 2 −HCO 3 −~-10‰) (Zeebe and Wolf-Gladrow, 2001), as well as the different photosynthetic pathways and degrees of "leakage" between photosynthetic cells and the ambient seawater (Carvalho et al, 2015). Algal respiration may exhibit some small isotopic fractionation (~3‰), with resulting changes reflected in the δ 13 C DIC (Carvalho and Eyre, 2011). We also ignored any potential contributions of air/sea CO 2 fluxes to the δ 13 C DIC variability because we calculated small air/sea CO 2 fluxes.…”