CarIN

Carbon isotope fractionation during leaf and root respiration as a function of nitrogen nutrition (CarIN – Carbo Iso Nitrogen)

Context

Increasing concentrations of atmospheric CO₂ and reactive nitrogen in the environment are raising questions about the interaction between plant carbon and nitrogen cycles and how this interaction will be influenced by changing climatic conditions. Uptake and assimilation of inorganic nitrogen are processes which will influence the energy and carbon metabolism of plants considerably. These effects have to be regulated by a mechanism involving the enzymes Phosphoenolpyruvate carboxylase (PEPc) and Malic enzyme (ME), which fix and release CO₂ in dependence of the nitrogen form and its place of assimilation (leaves vs. roots). Depending on a plant´s N nutrition, these enzymes are differently distributed between leaves and roots. These differences together with very different carbon isotopic signatures (δ¹³C) of CO₂ in air vs. soil air should be mirrored in δ¹³C values of respired CO₂ from leaves vs. roots, but also in δ¹³C of organic acids and related amino acids.

Objectives

Within CarIN, we would like to answer the following questions:

• How does the type of nitrogen fertilization (nitrate vs. ammonium) influence the release of leaf and root respired CO₂ and its isotope fractionation relative to putative substrates?
• To what extent does the site of nitrate reduction (roots vs. leaves) affect the release of CO₂ respired by roots and leaves and its δ¹³C value as compared to the substrates?
• Do nitrogen source and site of assimilation explain the observed differences in δ¹³C values between autotrophic and heterotrophic plant tissues?