Biology and Biogeochemistry

Isotopic signatures in a wide variety of complex organic compounds can reveal unique insights in biological and biogeochemical process. This is true as chemical and physical processes lead to changes in the natural isotope composition of organic compounds. The isotopes ¹³C, ¹⁸O, ¹⁵N and ²H provide scientists with a wealth of information on the origin of compounds, pathways of metabolism, synthesis and diagenesis as well as conditions of formation, and more.

Research topics include the study of plant structure, growth and differentiation, reproduction, biochemistry and primary metabolism, development, diseases and evolutionary relationships, plant taxonomy, as well as the study of interactions among organisms and their environment. Revealing metabolic processes within plants is possible by quantifying the imposed isotopic signature. Under controlled conditions in a laboratory plant chamber, environmental parameters such as temperature, air humidity, soil moisture and light intensity can be varied, and the isotopic signature quantified. Studying these processes allows to partition CO₂ fluxes in and out of ecosystems and ultimately leads to a better understanding of plant life.

Isotope ratio analysis of organic components

Compound-specific isotopic analysis of organic compounds is a useful approach for tracking the origin and fate of carbon and nitrogen in biogeochemical studies. When it comes to investigating metabolic pathways, GC-IRMS is a powerful technique, for either conducting tracer experiments or by studying the natural abundance of ¹⁵N or ¹³C in amino acids. Nitrogen content is usually low in organic compounds, so the determination of ¹⁵N/¹⁴N ratios is much more demanding than the determination of carbon isotope ratios.

Plant metabolism and nutrition

Scientists can use stable isotope composition of plant material to understand processes associated with plant metabolism. For example, during photosynthetic CO₂ fixation, fractionation of stable carbon isotopes occurs and, consequently, plants are generally depleted in the heavier carbon isotope, ¹³C. Isotopic fractionation in plants is caused by physical and biochemical factors. The two major types of plants, C3 and C4 fixation plants, have different biochemical pathways with the heavier isotope ¹³C being more (C3) and less (C4) depleted. This distinction can be used in a variety of applications.

Similarly ¹³C can be used at compound level to study metabolic pathways within plants. Organic acids are involved in various anabolic and catabolic processes of metabolic pathways, such as citric acid cycle, synthesis of amino acids and fatty acids. They participate in the regulation of the stomata, control ion equilibrium in cells, and participate in the refixation of ammonium as well as to the adsorption of nutrients such as phosphorus, iron, copper, manganese, and zinc. Compound-specific isotope analysis has been increasingly used to study metabolic pathways and their regulation. Thermodynamic and kinetic isotope effects discriminate isotopes in metabolic reactions and generate products with characteristic isotopic signatures.

Proxies to reconstruct biological processes in the past

Isotopes and elemental ratios within biological samples can be used to understand aspects of the organisms history. For example, elemental ratios can be used to reconstruct growth history of coral skeletons, and isotope ratios can be used to track the migration of animals through different ecological regions.