engleski

C-isotope composition od freshwater submerged mosses as an indicator of carbon during photosynthesis

Carbon isotopes compositions (a14C and δ13C) of freshwater submerged mosses and of dissolved inorganic carbon (DIC) were measured in the karst region of Croatia - at the Plitvice Lakes and along the water path of the Zrmanja and Krupa rivers. The moss samples were identified and they all belong to the C3 type plants regarding the photosynthesis pathway. The carbon isotope composition of mosses was compared to that of DIC and of atmospheric CO2, i.e., carbon reservoirs from which mosses pull carbon for photosynthesis. The current measured values at the Plitvice Lakes region were compared to the values measured 30 years ago, when the a14C of the atmosphere was about 30 % higher than today (Srdoč et al. 1986 ; Marčenko et al. 1989). The share of atmospheric carbon to carbon from DIC incorporated in mosses (ωatm) was calculated. Most moss species had ωatm values between 0 % and 66 %. A good correlation found for δ13Cmoss vs. ωatm gives a potential of using fossil mosses found in inactive tufas in determination of age of tufa formation, which is important for reconstruction of rivers’ palaeoflow, palaeoclimate and palaeoenvironment. However, two species of mosses (Cinclidotus aquaticus and Ptychostomum pseudotriquetrum) had a14C values bellow the a14CDIC which implied that they incorporated carbon only from DIC, i.e. that they turned to anabiosis during dry periods. Therefore, these moss species can be used as an indicator of an average a14C of DIC which is used to determine the initial activity of secondary carbonates (tufa and lake sediments) at the sampling sites. Values of a14CDIC for grab samples can have fluctuations depending on the water levels and are therefore not as reliable as the a14C values of composite samples such as the anabiotic moss species. From ωatm and δ13Cmoss values, the 13C fractionation between DIC and organic tissue of a moss was calculated (εDIC-moss) and it ranged from -50 ‰ to -29 ‰ which was probably the result of moss adjustment to synthesize primarily atmospheric CO2. For comparison, the 13C fractionation between atmospheric CO2 and organic tissue of a C3 plant, εatm-plant is ~-20 ‰. Correlation of εDIC-moss vs. ωatm showed the following pattern: 1) true aquatic moss species fractionated more if they contained more atmospheric C, and 2) moss species growing on wet rock fractionated more when they grew in higher water flows. Acknowledgement The work was funded by the project HRZZ-IP-11- 2013-1623 Reconstruction of the Quaternary environment in Croatia using isotope methods (REQUENCRIM), Croatian Science Foundation, and the Project with the Plitvice Lakes National Park. We are thankful to D. Borković for assistance in statistical analyses. References: Marčenko E., Srdoč D., Golubić S., Pezdič J., Head M.J. (1989) Carbon uptake in aquatic plants deduced from their natural 13C and 14C content. Radiocarbon 31/3, 785-794. Srdoč D., Krajcar Bronić I., Horvatinčić N., Obelić B. (1986) Increase of dissolved inorganic carbon along a river course. Radiocarbon 28/2A, 515-521.

submerged mosses ; carbon isotopes

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