Carbon isotope fractionation in karst aquatic mosses

Radiocarbon activity (a¹⁴C) and ¹³C composition (δ¹³C) were measured in hygrophyte and mesophyte (land) mosses collected in the natural habitat of the Plitvice Lakes and along the Zrmanja and Krupa Rivers (typical continental and Mediterranean climates, respectively), Croatia. a¹⁴C and δ¹³C values of mosses, of atmospheric CO₂ and dissolved inorganic carbon (DIC) were compared with contemporary data and with data from 30 years ago at the Plitvice Lakes when ¹⁴C activity of atmospheric CO₂ was ∼30% higher. A positive correlation between a¹⁴C_moss and δ¹³C_moss was observed for all data reflecting the change of carbon isotopic composition in DIC along the water flows and in atmospheric CO₂ regardless of the climatic regions and historic period. Fraction of the atmospheric carbon in moss $$ and carbon fractionation factor from aquatic CO₂ (DIC) to moss tissue $$ were calculated for each individual moss. Three species of mosses had ω_atm.C ∼ 0 % implying that they turn to anabiosis during dry periods. The relation $$ differentiates true aquatic and amphiphyte mosses. The first had a statistically significant negative correlation between $$ and $$. The amphiphyte mosses had lower $$ with higher water flow rates.