engleski

Carbon isotope fractionation during photosynthesis in submerged moss and aquatic plants

Radiocarbon activity (a14C) and ratio of stable isotopes 13C/12C (delta13C values) were measured in plant samples collected 2011-2012 in the natural habitat of the Plitvice Lakes, Croatia: terrestrial moss, water submerged moss, marsh and aquatic plants. All collected samples are C3 photosynthetic cycle plants. The a14C and delta13C values of the plant tissue were compared with values of carbon reservoirs the plants use in photosynthesis: atmospheric CO2 and/or dissolved inorganic carbon (DIC) as well as with the carbon isotope composition of plants measured 30 years ago [1]. The fraction of each carbon reservoir in plants was determined and the 13C fractionation factor between DIC and organic tissue of a plant was calculated. Since there were no systematic paired measurements for a14CDIC and a14C of plants at some locations in the old data set, we approximated the missing a14CDIC values by the values taken from [2]. There is a very good correlation between a14C and delta13C of moss plant tissue in both periods which is a result of variation of the ratio of atmospheric and dissolved inorganic carbon in moss. The fraction of atmospheric carbon in submerged mosses ranges from 8 to 66 %. Calculated 13C fractionation factor between DIC and organic tissue of moss is -41 ± 3 ‰. Aquatic plants (algae, submersed species) sampled from ~30 cm depth show higher fraction of atmospheric carbon (~20 %) than a sample from 14 m depth (~0 %). Floating plants have 15 – 20 % of atmospheric carbon, while emersed plants have 90 – 100 % of atmospheric carbon (marsh plants, sedge, grasses). Calculated 13C fractionation factor between DIC and plant tissue for submersed and floating plants is -22 ± 3 ‰, which is the same as the 13C fractionation factor between the atmospheric CO2 and plant tissue for C3 plants. Emersed samples have higher dispersion in 13C fractionation factor values (from -9 ‰ to -147 ‰). The difference between the determined 13C fractionation factors for mosses and for aquatic plants (algae and floating plants) could be a result of different plant adjustment to photosynthesis of HCO3-(aq) and CO32-(aq) molecules from DIC. Mosses are known to be adjusted to photosynthetic assimilation of CO2 there is probably an extra step of transformation of HCO3-(aq) and CO32-(aq) to CO2 resulting in a larger 13C fractionation factor between DIC and plant tissue for mosses than for aquatic plants. [1] Marčenko E, Srdoč D, Golubić S, Pezdič J, Head MJ. Radiocarbon 31 (1989) 785-794. [2] Srdoč D, Krajcar Bronić I, Horvatinčić N, Obelić B. Radiocarbon 28 (1986) 515-521.

Carbon isotope fractionation ; photosynthesis ; submerged moss ; aquatic plants

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