An analysis of the variability in δ 13 C in macroalgae from the Gulf of California: indicative of carbon concentration mechanisms and isotope discrimination during carbon assimilation

[摘要] The isotopic composition of carbon in macroalgae ( δ 13 C) ishighly variable, and its prediction is complex concerning terrestrialplants. The determinants of δ 13 C macroalgal variations wereanalyzed in a large stock of specimens that vary in taxa and morphology and werecollected in shallow marine habitats in the Gulf of California (GC) withdistinctive environmental conditions. A large δ 13 C 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. Environmentalconditions influenced the δ 13 C macroalgal values but did notchange the physiology, which is most likely inherently species-specific.Values of δ 13 C were used as indicators of the presence orabsence of carbon concentrating mechanisms (CCMs) and as integrative valuesof the isotope discrimination during carbon assimilation in the life cyclemacroalgae. Based on δ 13 C signals, macroalgae were classifiedin three strategies relative to the capacity of CCM: (1) HCO 3 - uptake ( δ 13 C  >   −10  ‰), (2) using amix of CO 2 and HCO 3 - uptake ( - 10 δ 13 C  >   −30  ‰), and (3) CO 2 diffusiveentry ( δ 13 C    −30  ‰). Most speciesshowed a δ 13 C that indicates a CCM using a mix of CO 2 andHCO 3 - uptake. HCO 3 - uptake is also widespread among GCmacroalgae, with many Ochrophyta species. Few species belonging toRhodophyta relied on CO 2 diffusive entry exclusively, while calcifyingmacroalgae species using HCO 3 - included only Amphiroa and Jania . The isotopicsignature evidenced the activity of CCM, but it was inconclusive about thepreferential uptake of HCO 3 - and CO 2 in photosynthesis andthe CCM type expressed in macroalgae. In the study of carbon use strategies,diverse, species-specific, and complementary techniques to the isotopic toolsare required.

[学科分类] 大气科学