Root system architecture reorganization under decreasing soil phosphorus lowers root system conductance of Zea mays

The global supply of phosphorus (P) is decreasing. At the same time, climate change is reducing the availability of water in most regions of the world. Insights into how decreasing P 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 P fertilization levels focusing especially on the root system's conductance. A rhizotron experiment with soils ranging from severe P 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 P levels.

We observed changes in the root system architecture, characterized by decreasing crown root elongation and reduced axial root radii with declining P availability. Modelling revealed that only plants with optimal P availability sustained a high root system conductance, while all other P levels led to a significantly lower root system conductance, under both light and severe P deficiency.

We postulate that P 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 organization of the root system, rather than its overall size, is critical for estimating important root functions.