Mechanistic interpretation of carbon isotope discrimination by marine macroalgae and seagrasses

Abstract

The literature, and previously unpublished data from the authors’ laboratories, shows that the δ13C of organic matter in marine macroalgae and seagrasses collected from the natural environment ranges from –3 to –35‰. While some marine macroalgae have δ13C values ranging over more than 10‰ within the thallus of an individual (some brown macroalgae), in other cases the range within a species collected over a very wide geographical range is only 5‰ (e.g. the red alga Plocamium cartilagineum which has values between –30 and –35‰). The organisms with very negative δ13C (lower than –30‰) are mainly subtidal red algae, with some intertidal red algae and a few green algae; those with very positive δ13C values (higher than –10‰) are mainly green macroalgae and seagrasses, with some red and brown macroalgae. The δ13C value correlates primarily with taxonomy and secondarily with ecology. None of the organisms with δ13C values lower than –30‰ have pyrenoids. Previous work showed a good correlation between δ13C values lower than –30‰ and the lack of CO2 concentrating mechanisms for several species of marine red algae. The extent to which the low δ13C values are confined to organisms with diffusive CO2 entry is discussed. Diffusive CO2 entry could also occur in organisms with higher δ13C values if diffusive conductance was relatively low. The photosynthesis of organisms with δ13C values more positive than –10‰ (i.e. more positive than the δ13C of CO2 in seawater) must involve HCO3- use.

Algal evolution in relation to atmospheric CO 2 : carboxylases, carbon-concentrating mechanisms and carbon oxidation cycles

“…Modified from [10]. Further details and references are given in the text and in [10][11][12]101,105,106,110,[112][113][114][115][116][117][118][119][120]. Predicted resource costs of synthesizing and operating a photosynthetic apparatus using a CCM relative to one relying on entry of CO 2 by diffusion [66,[68][69][70][71]73,91,105,121] Pleistocene, they would have had to have survived intervening period(s) of higher CO 2 and higher temperatures.…”

“…General references on earliest known occurrence of algae: [6][7][8]. References on presence or absence of CO 2 -concentrating mechanisms (CCMs): [9][10][11][12][13][14]. CCM absent in all ?…”

“…Entry of CO 2 to Rubisco by diffusion is found today in the majority, by species number and contribution to global primary productivity, of terrestrial oxygenic photosynthetic organisms, but in a minority of oxygenic photosynthetic organisms in aquatic environments where photolithotrophs with CCMs predominate [11][12][13]34,67,79,[98][99][100][101] (table 1). The references just cited show that CCMs are very widely distributed among algae, both phylogenetically and geographically, although they seem to be absent from chrysophycean and synurophycean algae [9].…”

Stable Isotope (δ13C, δ15N, δ18O, δD) Composition and Nutrient Concentration of Red Sea Primary Producers

“…While in continental plants carbon isotope composition depends mainly of specific enzymatic mechanisms of primary production (e.g., C3, C4, or CAM) and WUE (Water Use Efficiency), in marine plants, all C3 (RuBisCO) depends on the supply and source of carbon (CO 2 or HCO 3 -) and specific mechanisms of primary production (e.g., C3 or C4), light level, plant size and growth rate, among others (Farquhar et al, 1989;Descolas-Gros and Fontungne, 1990;Maberly et al, 1992;Hemminga and Mateo, 1996;Burkhardt et al, 1999;Raven et al, 2002). As such, the isotope composition differs significantly from phytoplankton, with δ 13 C signatures of about −22‰, to seagrasses, often growing under CO 2 -limitation leading to heavy isotopic signatures with values of around −8‰ (Hemminga and Mateo, 1996).…”

Latitudinal trends in stable isotope signatures and carbon concentrating mechanisms of northeast Atlantic rhodoliths

“…taken up by marine macroalgae influences the stable carbon isotope signature of the tissue (Maberly et al, 1992;Raven et al, 2002). Therefore, the ratio of stable carbon isotopes (∂ 13 C) in macroalgal tissue can be used as an indicator of whether or not a carbon concentrating mechanism is present (Raven et al, 2002) using the formula 5 Many studies have investigated the presence/absence of CCMs using ∂ 13 C signatures across taxonomic groups and environmental gradients such as depth/light, CO 2 , and latitude (Hepburn et al, 2011;Moulin et al, 2011;Raven et al, 2011;Stepien, 2015;Stepien et al, 2016), but so far few studies have investigated the flexibility of CCMs in a single species or group of marine macroalgae (Cornelisen et al, 2007;Cornwall et al, 2017;Mackey et al, 2015).…”