Experiments were conducted across three work packages (WP), addressing the three project objectives:
WP1: Demonstrate how RSA of contrasting NILs (narrow/wide angle) affects the response to heterogeneously distributed P fertiliser in time
WP2: Determine how contrasting NILs (narrow/wide angle) respond plastically to a fertiliser P band and relate this to soil chemical properties (labile P, speciation of elements) across the soil-fertiliser interface
WP3: Demonstrate how citrate exudation along a root axis affects soil pH and availability of P for contrasting NILs (high citrate efflux /no citrate efflux)
Within each WP, main activities have involved plant growth experiments followed by in-situ imaging of root growth and/or soil chemical changes around roots. Major techniques include the use of (synchrotron and lab-based) 3D X-ray computed tomography (CT), diffusive gradients in thin films (DGT) coupled with laser ablation-ICP-MS (LA-ICP-MS), Planar optodes, and X-ray absorption near-edge structures (XANES).
Project results demonstrate:
1. synchrotron-based X-ray CT is a potential novel tool for studying plastic responses of root system architecture, in soil, at high spatial resolution.
2. the reactions of P in soil determine the movement and availability of P in and around a fertiliser band, depending on the interaction between fertiliser type and soil type. The resulting P availability dynamics, in turn, determine the occurrence of plastic root responses in a largely genotype-independent manner.
3. the P depletion gradient along the root axis was greater with a high citrate efflux from roots, but this was associated with an increase rather than the expected decrease of rhizosphere pH. We hypothesise that control of the rhizosphere pH was driven by the cation-anion balance, in which excess uptake of nitrate by the plant root would have led to alkalinization rather than acidification - this would require additional experimentation.
Although the project did not directly target market applications or environmental challenges, the tools and knowledge generated may support future research addressing societal needs, including those related to plant breeding, agronomy and sustainability. For example, methodology may ultimately develop towards new ways of selecting root traits for breeding programs. In addition, the X-ray CT method serves as a ‘proof-of-concept’ for in-situ investigation of root-soil interactions, opening a relevant new field for future research and applications.
Data have been disseminated through oral presentations at scientific conferences, peer-reviewed manuscripts, and on-campus stakeholder visits. The planned manuscripts have either been published (van der Bom et al., 2025), or are in preparation for submission in line with the original dissemination plan.
