PhD Defence: Zhiwei Song

Thesis title: The phenotypic plasticity of rice roots - The responses of adaptive root traits to soil water gradients

Supervisor: Ole Pedersen

Assessment committee:
Lars Båstrup-Spohr, Department of Biology (Chair)
Dennis Konnerup, SEGES Innovation
Gustavo Striker, University of Buenos Aires

Abstract

Understanding how plant roots adapt to varying soil moisture conditions is essential for improving crop resilience under environmental stress. This thesis examines the key root traits that acclimate to soil flooding, with a focus on radial water loss (RWL) under low water potential. Additionally, it explores whether root acclimations to soil flooding enhance plant tolerance to subsequent water deficit conditions. The study assesses the anatomical and physiological adaptations of roots and rhizomes in Oryza longistaminata under different water availabilities and evaluates physiological integration through interconnected  rhizomes under heterogeneous water deficit stress. The first part of the study demonstrates that, in addition to the presence of a radial O2 loss (ROL) barrier, increased root diameter and reduced root porosity are crucial for minimizing RWL, thereby improving water retention under both flooded and drought conditions. This research also provides the first report of an ROL barrier being induced under low water potential in rice roots. Furthermore, it reveals that root acclimations to soil flooding offer advantages during subsequent water deficit periods, indicating a mechanism of cross-stress tolerance. The study also  investigates physiological integration within interconnected rhizomes in O. longistaminata, showing that such integration can alleviate the effects of spatially heterogeneous water stress. Moreover, both rhizomes and roots of O. longistaminata exhibit similar responses to varying water regimes. These findings offer valuable insights into the adaptive strategies of roots and
rhizomes and underscore the potential for applying these mechanisms in breeding programs to enhance water use efficiency and stress tolerance in rice cultivars.