Ecological Implications Of The ẟ13c Values of Plant Species Growing in Natural Environment, Greenhouse and Plant Respired Carbon Dioxide (Captured as Carbonate)

13 C values have been used to differentiate the C 3 plant species from the C 4 species. Light isotope ( 12 C) is favoured against the heavier isotope ( 13 C) during the carbon fractionation in plant species. The 13 C values of terrestrial plant are useful in diverse applications in ecological, forensic, microbial diagnostic, biochemical and other scientific studies. There is variation of the 13 C values between the intraspecies grown in the greenhouse under controlled climatic conditions except respired carbon dioxide concentration. Also, 13 C values variation exist between interspecies, both grown in the greenhouse and field conditions. Isotopic composition of respired carbon dioxide (carbonate, CO 3 -) was different from that of plant carbon dioxide (carbonate, CO 3 -) and may be accounted due to respired carbon dioxide refixation. Further differences in the respired carbon exist between the C 3 and C 4 plant 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 13 C values. Different climatic factors and carboxylating enzymes explain the variation in the 13 C values within and amongst the C 3 and C 4 plant species. Furthermore, the variation in 13 C 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 the 13 C values.