Soil salinity effect on carbon isotope composition of plant biomass

The analysis of the carbon isotopic data available from the literature evidences in favor of the significant effect of salinity on plant and photosynthesizing alga biomass. The nature of this effect is explained in terms of oscillation model of carbon isotope fractionation in photosynthesis. The data interpretation and conclusions are compared with those obtained from commonly adopted steadystate model of carbon isotope fractionation in photosynthesis. It is shown that the first model gives a new explanation and substantiation on the causes of different response of carbon isotope ratio of glycophyte (salt-sensitive plants) and halophyte (salt tolerant) plant biomass to salinity change. A new explanation for inversion of carbon isotope effect sign in C4-plants in response to salt stress is given. Under salt stress due to the increase of CO2 leakage from bundle sheath back to mesophyll cells the isotope fractionation in C4-plants becomes similar to that in C3-plants, i.e. the contribution of isotope fractionation in RuBP carboxylation grows up and results in 12 C –enrichment of biomass and inversion of isotope effect sign as well.