Comparisons of ?13C values in leaves of aquatic macrophytes from different habitats in Britain and Finland; some implications for photosynthetic processes in aquatic plants

Abstract

The δC values of submerged aquatic plants from contrasting but relatively defined habitats, and the δC values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the δC values of dissolved inorganic carbon in the water were also measured. Plant δC values in the vicinity of-40 to-50‰ were found in rapidly flowing spring waters with carbonate δC values of-16 to-21‰, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO via RuP carboxylase. Plant δC values in the vicinity of-10 to-15‰ in sluggish water with carbonate δC values of about-5‰ were observed, consistent with the notion that boundary layer diffusion and/or HCO uptake may determine the δC value of submerged aquatic plants in these circumstances. Comparisons of δC values of the same or related species growing in waters of similar carbonate δC value but different flow rates confirmed this view; more negative δC values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the δC values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The δC value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO, as opposed to atmospheric carbon. The contributions of these variations in δC of the carbon source, and of isotope fractionation in diffusion, to the δC value of submerged parts of dimorphic plants is discussed.

Marine mammals and the community structure of the Estuary and Gulf of St Lawrence, Canada: evidence from stable isotope analysis

“…Macroalgae from the infralittoral (Laminaria longicruris) and intertidal (Ascophyllum nodosum) zones differed markedly in their δ 13 C values. This large variation (4 ‰) is likely attributable to lower turbulence and recycling of dissolved C in the boundary layer of infralittoral species, resulting in a progressive increase in 13 C concentration, as well as greater access by intertidal species to 13 C-depleted air CO 2 during emersion (Osmond et al 1981, Surif & Raven 1990. Despite this variation, macroalgae still differed from POM by 5.3 to 9.1 ‰.…”

“…Although this makes C a less reliable index of trophic position, it is still useful to the study of diet through its use as a tracer of sources of primary productivity. Primary producers vary in their isotopic C signatures according to their origin (terrestrial or aquatic), C pool used and concentration (CO 2 in air, dissolved CO 2 or HCO 3 -in water), prevailing C pathways (C 3 vs C 4 plants), and the condition of the surrounding environment (well mixed or stagnant) (Smith & Epstein 1971, Osmond et al 1981, France 1995, Fry 1996. These properties assist in discriminating between animals which obtain their resources from terrestrial versus aquatic, benthic versus pelagic or inshore versus offshore environments (Ramsay & Hobson 1991, Smith et al 1996, Page 1997.…”

Food resources and ingestion patterns of insects along a west coast, South Island, river system∗

“…A particularly dramatic demonstration of these 2 carbon pathways is provided by stable carbon data for insects and their potential foods from a very small, slow-flowing stream in the Maimai Experimental Catchment Area (Winterboum & Rounick unpublished). In this stream, algae were highly depleted in 13 C (-39.9 %o), indicating use of biogenic (respiration) CO 2 for photosynthesis (Rau 1978;Osmond et al 1981), and stone-surface dwelling Deleatidium larvae which appeared to ingest few algae were correspondingly depleted in 13 C (-41.8 %o). In contrast, the 6 13 C value for Spaniocercoides cowleyi, a small detritivorous stonefly which was abundant in muddy pools choked with fine particles was -27.5 %o, consistent with that of its detrital food (-28.1 %o).…”

Carbon Uptake in Aquatic Plants Deduced From Their Natural 13C and 14C Content

“…Thus, Q13C = (bl C plant -s13C source carbon) was introduced (Osmond et al, 1981;Richardson et al, 1984).…”

“…The large scatter in 813C values of aquatic plants has been partly attributed to variations in the s13C content of the carbon source itself: dissolved inorganic carbon (DIC) in water. 13C values in several aquatic plants reflect, besides the photosynthetic pathway, the difference in water chemistry, water depth, water flow, seasonal and other ecological factors (Osmond et al, 1981), which makes the interpretation of isotopic data even more difficult. Thus, in aquatic plants, of which most fall within the C3 category, at least biochemically, the situation is complicated by the influence of various ecological factors as well as lack of knowledge of the exact photosynthetic steps following carbon uptake.…”