Abstract
Abstract. The isotopic composition of carbon in macroalgae (δ13C) is highly variable, and its prediction is complex concerning terrestrial plants. The determinants of δ13C macroalgal variations were analyzed in a large stock of specimens that vary in taxa and morphology and were collected in shallow marine habitats in the Gulf of California (GC) with distinctive environmental conditions. A large δ13C variability (−34.6 ‰ to −2.2 ‰) was observed. Life-forms (taxonomy 57 %, morphology and structural organization 34 %) explain the variability related to carbon use physiology. Environmental conditions influenced the δ13C macroalgal values but did not change the physiology, which is most likely inherently species-specific. Values of δ13C were used as indicators of the presence or absence of carbon concentrating mechanisms (CCMs) and as integrative values of the isotope discrimination during carbon assimilation in the life cycle macroalgae. Based on δ13C signals, macroalgae were classified in three strategies relative to the capacity of CCM: (1) HCO3- uptake (δ13C > −10 ‰), (2) using a mix of CO2 and HCO3- uptake (-10<δ13C > −30 ‰), and (3) CO2 diffusive entry (δ13C < −30 ‰). Most species showed a δ13C that indicates a CCM using a mix of CO2 and HCO3- uptake. HCO3- uptake is also widespread among GC macroalgae, with many Ochrophyta species. Few species belonging to Rhodophyta relied on CO2 diffusive entry exclusively, while calcifying macroalgae species using HCO3- included only Amphiroa and Jania. The isotopic signature evidenced the activity of CCM, but it was inconclusive about the preferential uptake of HCO3- and CO2 in photosynthesis and the CCM type expressed in macroalgae. In the study of carbon use strategies, diverse, species-specific, and complementary techniques to the isotopic tools are required.
Highlights
Macroalgae show a wide diversity of thallus morphologies, structural organization, and various photosynthetic pigments (e.g., Chlorophyll a, b, phycocyanin) (Lobban and Harrison, 1994)
An analysis of the biogeographical diversity among sectors evidenced that P3 (43 genera of 63, 68 %) and C3 (63 %) in the north recorded the highest number of the genus, followed by C1 (38 %) and P1 (29 %) in the south, and P2 (27 %) and C2 (22 %)
Regression coefficients were estimated for each fitted regression model, which are used as indicators of the quality of the regression (Burnham and Anderson, 2002; Draper and Smith, 1998) as was described in Methods; the description of our results focused on the coefficients of determination (R2 and adjusted R2)
Summary
Macroalgae show a wide diversity of thallus morphologies (e.g., filamentous, articulated, flattened), structural organization (e.g., surface area : volume ratio), and various photosynthetic pigments (e.g., Chlorophyll a, b, phycocyanin) (Lobban and Harrison, 1994). The interaction of morphologies and photosynthetic pigments is classified into dozens of groups (Balata et al, 2011; Littler and Littler, 1980; Littler and Arnold, 1982). The mixture of chlorophyll (a, b) and carotenoids is dominant in Chlorophyta, and chlorophyll (a, c) and fucoxanthin carotenoid are dominant in Ochrophyta, while Rhodophyta contains chlorophyll (a, d), carotenoid, and a mixture of phycobilin (e.g., phycocyanin, phycoerythrin, allophycocyanin) (Bold and Wynne, 1978; Gateau et al, 2017; Masojidek et al, 2004). Velázquez-Ochoa et al.: An analysis of the variability in δ13C in macroalgae
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