Three-dimensional root architectural plasticity in rice: mechanistic responses to water deficit stress

Understanding root architectural plasticity under water deficit is essential for improving rice drought tolerance. However, whether drought-tolerant and drought-sensitive cultivars differ in qualitative spatial strategies or merely in the magnitude of plastic responses remains unresolved, and conventional destructive phenotyping cannot capture three-dimensional dynamics.

We developed WSroots, an L-system-based three-dimensional model, and quantified root development in drought-tolerant HY73 and drought-sensitive Longliangyou Huazhan (LLYHZ) under polyethylene glycol-6000 (PEG6000) osmotic stress at 0, 50, 125 and 200 g kg^-1 for 28 days in hydroponic culture. HY73 maintained 25-30% of root length at 35-60 cm depth with only 25.2% total length reduction at 200 g kg^-1 PEG6000, whereas LLYHZ concentrated 65-70% of roots in the 0-15 cm surface layer with 39.6% reduction. Root diameter declined less in HY73 (9.3%) than in LLYHZ (14.8%), indicating superior structural resilience. Calibration accuracy reached a coefficient of determination (R²) of 0.986 (HY73) and 0.949 (LLYHZ).

The two cultivars employ qualitatively distinct strategies - deep exploration versus shallow expansion - rather than quantitative gradients of the same response. Deep-rooting maintenance is therefore a key target for drought-resilient rice breeding. WSroots provides a transferable framework for virtual phenotyping and irrigation design that can be extended to soil-based systems through water potential equivalence. © 2026 Society of Chemical Industry.