Dual labelling by 2H and 15N revealed differences in uptake potential by deep roots of chicory

Summary

Aims
Deep-rooted crops have been widely used in agricultural systems to access deep resources such as water and nitrogen (N). However, the potential of deep roots to take water and N at various depths have not been well studied. Here we used chicory (Cichorium intybus L.) to study the potential and dynamics of water and nitrogen uptake in deep soil layers (below 1 m).
Methods
Chicory plants grown in outdoor rhizotrons were labelled by injecting a 2H2O and Ca(15NO3)2 mixture into the soil column at 1.1, 2.3 and 3.5 m depth. Five, ten and twenty days after injection, 2H and 15N were traced in transpiration water and leaves.
Results
We found enriched 2H and 15N in water and plant samples, and both water and N uptake were observed down to 3.5 m. The 2H enrichment after injection at 1.1 m depth was 1552‰, almost 10 times higher than after injection at 2.3 m depth, which was 156‰. In contrast, injection at 1.1 and 2.3 m depth resulted in similar 15N enrichment of leaf samples.
Conclusion
Deep water uptake was found to be more sensitive to increased depth and reduced root intensity than N uptake, and labelled N was used more rapidly than labelled water. We propose several possible explanations for the discrepancies between deep water and N uptake, and further discuss the challenges of using isotopes and models in deep root studies.