Temporary growth cessation of wheat roots following defoliation

Defoliation triggers the remobilisation of root reserves to generate new leaves which can affect root growth until the shoot resumes net assimilation. However, the duration of root growth cessation and its impact on resource uptake potential is uncertain. Winter wheat was established in a 4 m high outdoor rhizobox facility equipped with imaging panels, sensors, and access points for tracer-labelling. The wheat was defoliated in autumn at early tillering and roots were imaged at a high-time resolution and analyzed by deep learning segmentation. The water and nitrogen (N) uptake were measured using time-domain reflectometer (TDR) sensors and 2H and 15N isotopes. Root penetration of wheat paused for 269 °C days (20 days) following defoliation after which it resumed at a similar rate to un-defoliated plants (1.8 mm °C days−1). This caused a substantial decrease in root density with an associated reduction in water and N uptake at maturity, especially from deeper soil layers (>2 m). Our results have significant implications for managing the grazing of dual-purpose crops to balance the interplay between canopy removal and the capacity of deep roots to provide water and N for yield recovery.