Inorganic carbon acquisition by aquatic photolithoatrophs of the Dighty Burn, Angus, U.K.: uses and limitations of natural abundance measurements of carbon isotopes

Abstract

SUMMARYThe '^C/'^C ratio (expressed as ^''^C) ot" benthic photolithotrophs in the Dighty Water (= Burn) were measured for comparison with that of the potential inorganic carbon sources, CO^ and HCO^ , in the Burn. The Burn water contains an average of 657 mmol m^ CO^ with rf'''C of -147?i^, and 1600 mmol m"'HCO^ with ^"C of -4-0%a. ^^"C values of riparian vegetation were also measured as contrihutors, after respiration in the soil or the Bum, to the (J'^C of inorganic carhon in the Burn. The potential range of differences in '•''C/'^C between dissolved CO., and plant organic C is set by the intrinsic 'KV'^C discrimination (a value) in CO^ fixation by Rubisco. Main results and conclusions are as follows, (i) A literature survey suggests that there is no convincing evidence that the a, values (rate constant for '-CO^ fixation relative to that for '''CO, fixation by Uubisco in the ab.sence of COt ransport limitation) for the 'lower plants' in the Burn (diatoms, green and red aigae, mosses) are significantly difterent from the well-estabhshed a,, values for the flowering plant enzyme, (ii) In confirmation of earlier work, the semi-erect 'streamer' gametophytes of the red alga Lcmanea mamilhsa and the moss Fontmalis anfjpyretica have S^^C values which can only be interpreted in terms of diffusive CO^ entry with minimal limitation of photosynthesis by CO^ diffusion, (iii) The semi-erect green aiga Cladophora glomerata and the flowering plant Ravum-ulus penidllotus ssp. pseudofluilons {formt-Tly var. calcareus)-^Te both able to use HCO.,". Their (^'''C \alues indicate that, if the HCO., -use system does not (as is likelv) discriminate significantly between '^C and '^C, then a substantial fraction of the inorganic C made available lo Rubisco must return to the medium, carrying '^C-inorgamc C not fixed by Rubisco. (i\') Two sets nf rt'^'C data from different hydrodynamic regimes (distance from leading edge of a flat stone; dift"erent size of thalli) show thai the attainable differences »i situ m thickness of the diffusion houndary layer do not alter the fractional limitation of photosynthesis of Cladophora by external diffusion of inorganic C, considered with HCO^" use. (vi) The encrusting red alga Hildenhrondia rivutaris has a rS'^C value suggestive of CO, as the morganic C source, hut not entirely ruling out HCO, . Marine species of both HUdenbraridia and Cladophora hax e i^'''C values which, even when corrected for source inorganic C ^^"'C values, are 10?™ tnore positive than the freshwater species, (vii) Mats of pennate diatoms were shown by pH-drift to be able lo use HCO^"; the relatively high (i.e. not very negative) ^''C value of these mats could relate to a relatively 'non-leaky' HCO.," acquisition mechanism and/or to limitation by external diffusion (e.g. through the mat).

Stable isotope analysis of the origins of zooplankton carbon in lakes of differing trophic state

“…Variation in phytoplankton δ 13 C reflects both the isotopic signature of the inorganic carbon source and the degree to which fractionation occurs during photosynthesis. In freshwaters, the source of DIC may have a particular impact on phytoplankton δ 13 C (Raven et al 1994) and it is a shortcoming of this study that a successful protocol for determination of the δ 13 C of DIC was not in our use at the time of the survey. Literature δ 13 C values for lakewater DIC are often around -5‰, although hypolimnetic DIC may be more 13 Cdepleted during stratification (Keough et al 1996).…”

Influences of different nitrogen sources on nitrogen- and water-use efficiency, and carbon isotope discrimination, in C 3 Triticum aestivum L. and C 4 Zea mays L. plants

“…The d 13 C value of the organic C in the specimens was determined as described by Raven et al (1994); 1 mg of each ground sample was analysed in a VG ISOGAS SIRA Series II isotope ratio mass spectrometer (UG Analytical, Crewe, UK) with a Carlo-Erba CHN Analyser employed as a combustion unit. The 13 C/ 12 C ratios are expressed in the d notation, and d 13 C is de®ned as the 13 C/ 12 C of organic C in a plant (a sample) compared to inorganic C (a standard) by the following expression:…”

Implications of 13C natural abundance measurements for photosynthetic performance by marine macrophytes in their natural environment

“…(4), adlfl is taken as 1.0004 (O'Leary 19841, while aCarb is taken as 1.028. The rationale for aCarb = 1.028 is that a~~~~~~~ for red and green algae is, on the basis of dissolved CO2, 1.029 (Raven et al 1994). These values are not known to be influenced by pH, salinity or temperature (O'Leary 1984, Faraquhar et al 1989, Raven et al 1994.…”

“…The rationale for aCarb = 1.028 is that a~~~~~~~ for red and green algae is, on the basis of dissolved CO2, 1.029 (Raven et al 1994). These values are not known to be influenced by pH, salinity or temperature (O'Leary 1984, Faraquhar et al 1989, Raven et al 1994. Correction for the contribution of PEPC and CPS to aCarb is based on their a values, and the assumption that, in algae, essentially all of the CPS and PEPC activity relates to the synthesis of C skeletons for N assimilation for a (molar) C:N ratio in the algae of 10 (see Raven & Farquhar 1990).…”

“…For calcified specimens, a 1 h treatment with 100 m01 HC1 m-3 followed by a rinse in distilled water was used to remove the CaCO,. The 6I3C value of the organic C in the specimens was determined as described by Maberly et al (1992) and Raven et al (1994). In brief, dried material was ground, and 1 mg samples were analysed in a VG ISOGAS SIRA Series I1 isotope ratio mass spectrometer with a Carlo-Erba CHN analyser employed as a combustion unit.…”