Adjustment of Root System Architecture and Root Function in Response to Multifactorial Abiotic Stress

ABSTRACT

The root of land plants is a remarkably adaptive organ. Unlike the shoot with its main functions in light harvesting and photosynthesis, sexual reproduction and diaspore distribution, the root explores the soil for nutrient resources and water, while preferably avoiding zones of unfavorable conditions. Roots realize an extraordinarily flexible architecture and perceive and integrate environmental input parameters to optimize growth, architecture, and physiology. In nature, roots encounter a heterogeneous rooting environment characterized by combinations of negative and positive growth parameters, for example, nutrient availability, temperature, hypoxia, toxic metal ions, or compacted soil, necessitating research on multifactorial stress effects on roots. While many studies have addressed the combination of altered nutrient status, in particular nitrogen and phosphorus, and other environmental stress factors such as drought, temperature, and soil compaction, fewer studies addressed climate change‐related combinations of stressors such as heat, drought, and hypoxia. The decisive mechanism of environmental input integration targets root growth and architecture, but also exudation. The adjustment is realized by altered activity of apical meristems for root elongation, the pericycle for lateral root initiation and formation, the development of adventitious roots, and root thickening by cambial activity and senescence. This review presents selective case studies to exemplarily summarize current experimental approaches and obtained knowledge on root responses to multifactorial environmental constraints with focus on assimilate‐, redox‐, and auxin‐dependent regulation. The review pinpoints the need to advance and harmonize our experimental approaches by investigating the sensory role and growth response of roots at the local and systemic level.