Isotope ratio mass spectrometry technique to follow plant metabolism. Principles and applications of ¹²C/¹³C isotopes

Isotope fractionations during biophysical and biochemical processes are at the origin of natural differences in heavy-to-light isotope ratios (e.g. ¹³C/¹²C, ²H/¹H, etc.) among biosphere components (soil organic matter, vegetation and atmospheric CO₂), metabolites and atomic positions within molecules. The natural abundance in stable isotopes of biological common elements (C, H, O, N, S) is thus widely used as tracer or physiological marker to examine biochemical and ecophysiological mechanisms from the cellular to the ecosystemic scale. Since the pioneering studies on isotopic composition of plant organic matter in the 1980s, important methodological and technological advances have been made to improve the convenience, precision and rapidity of isotopic measurements. In this chapter, we explain the basics of isotopic composition and fractionation, and review the most important technical advances in plant biology. We focus on carbon stable isotopes since the natural ¹³C-distribution has proved to be a powerful tool to investigate carbon primary metabolism and respiratory flux patterns.