Root System Architecture Reorganization Under Decreasing Soil Phosphorus Lowers Root System Conductance of Zea mays

The global supply of phosphorus is decreasing. At the same time, climate change reduces the availability of water in most regions of the world. Insights on how decreasing phosphorus availability influences plant architecture are crucial to understanding its influence on plant functional properties, such as the root system's water uptake capacity. In this study, we investigated the structural and functional responses of Zea mays to varying phosphorus fertilization levels focusing especially on the root system's conductance. A rhizotron experiment with soils ranging from severe phosphorus deficiency to sufficiency was conducted. We measured the architectural parameters of the whole plant and combined them with root hydraulic properties to simulate time-dependent root system conductance of growing plants under different phosphorus levels. We observed changes in the root system architecture, characterised by decreasing crown root elongation and reduced axial root radii with declining phosphorus availability. Modeling revealed that only plants with optimal phosphorus availability sustained a high root system conductance, while all other phosphorus levels led to a significantly lower root system conductance, both under light and severe phosphorus deficiency. We postulate that phosphorus deficiency decreases root system conductance, which could mitigate drought conditions through a more conservative water use strategy, but ultimately reduces biomass and impairs root development and overall water uptake capacity. Our results also highlight that the organisation of the root system, rather than its overall size, is critical for estimating important root functions.