DGT exudates

Research context. Carboxylate exudation is a major process for plants to ensure adequate nutrient acquisition, particularly in phosphorus (P) deficient soils. Obtaining carboxylate samples from soil-grown roots is experimentally very challenging due to the low concentrations of carboxylates in the soil pore water and their fast mineralization by microbes. Consequently, most research so far has been conducted using artificial growth systems (e.g. hydroponics), many of which potentially affecting the composition and quantity of root exudates. Due to this significant technique gap, there is still a major knowledge gap concerning the spatial distribution of carboxylate exudates in the rhizosphere, as well as on the time-course of exudation across the vegetation period of crops. We have recently developed a low-invasive citrate exudate sampling method based on diffusive gradient in thin films (DGT, Figure 1), which is a significant improvement over existing techniques and enables repeated citrate sampling from soil-grown roots at very high spatial and temporal resolution.

Figure 1 Schematic display of carboxylate-sampling of plants which were grown in rhizotrones using DGT gels.

Objectives. In this project, we will

1. further develop our DGT citrate sampling method to include major carboxylate exudate compounds,
2. utilize the DGT chemical imaging functionality to develop mm as well as sub-mm resolution carboxylate exudation imaging workflows,
3. characterize the developed DGT carboxylate sampling methods for their capabilities and limitations, and
4. apply DGT carboxylate sampling to study the role of carboxylate exudation in the phosphorus acquisition efficiency of durum wheat genotypes across their vegetation period and at high spatial resolution.

Methods. Selected anion exchange resins will be characterized for their carboxylate binding properties. Spatial carboxylate distributions will be resolved by DGT gel cutting and by laser desorption ionization Fourier-transform ion cyclotron resonance mass spectrometry (LDI-FTICR-MS). Recovery of carboxylates by DGT will be quantified using microdialysis (artificial root probes) in combination with C-14 labelled carboxylate compounds. Numerical simulation of the sampling process and experimental comparison with alternative exudate sampling methods will demonstrate the capabilities and limitations of DGT carboxylate sampling.

Innovation. We will develop a low-invasive methodology to sample major carboxylate exudates from soil-grown roots, enabling sampling from entire root systems and root system parts, mapping at mm-scale resolution, imaging exudate gradients at sub-mm resolution and sampling repeatedly over the entire vegetation period. Using this novel methodology, unprecedented data on carboxylate exudation patterns in durum wheat root systems will be collected. This novel DGT carboxylate sampling methodology will overcome a major technique gap, and will contribute to developing/selecting crop cultivars with high phosphorus acquisition efficiency.

Literature:

Tiziani R, Puschenreiter M, Smolders E, Mimmo T, Herrera JC, Cesco S, Santner J, 2021. Millimeter-resolution mapping of citrate exuded from soil grown roots using a novel, low-invasive sampling technique. Journal of Experimental Botany, https://doi.org/10.1093/jxb/erab123.