Ecological implications of the ẟ13C values of plant species growing in natural environment, greenhouse and plant respired carbon dioxide (captured as carbonate).

Abstract

ẟ13C values have been used to differentiate the C3 plant species from the C4 species. Light isotope (12C) is favoured against the heavier isotope (13C) during the carbon fractionation in plant species. The ẟ13C valuesof terrestrial plant are useful in diverse applications in ecological, forensic, microbial diagnostic, biochemical and other scientific studies. There is variation of the ẟ13C values between the intraspecies grown in the greenhouse under controlled climatic conditions except respired carbon dioxide concentration. Also, ẟ13C values variation exist between interspecies, both grown in the greenhouse and field conditions. Isotopic composition of respired carbon dioxide (carbonate, CO3-) was different from that of plant carbon dioxide (carbonate, CO3-) and may be accounted due to respired carbon dioxide refixation. Further differences in the respired carbon exist between the C3 and C4plant species. Diffusion of carbon dioxide, interconversion of carbon dioxide and bicarbonate, assimilation of carbon dioxide by Ribulose bisphosphate carboxylase or Phosphoenol pyruvate carboxylase during carbon fractionation affect the final ẟ13C values. Different climatic factors and carboxylating enzymes explain the variation in the ẟ13C values within and amongst the C3 and C4 plant species.Furthermore, the variation in ẟ13C values may be caused by genetic differences in either leakiness of the bundle sheath cells due to light-use efficiency or by differences in the ratio of assimilation rate of stomatal conductance due to transpiration efficiency. Thus, both kinetics and thermodynamic modelling can be applied to explain the carbon fractionation process and theẟ13C values.