Exploiting the functionality of root systems for dry, saline, and nutrient deficient environments in a changing climate

Abstract

Increasing episodes of drought, lack of sufficient nutrients, exposure to toxic minerals, and soil compaction are just a few examples of the environmental constraints that the roots are exposed to during plant growth. Understanding how roots respond to these stresses is crucial for improving crop production under such conditions. Yet, investigating roots is a very difficult task and, therefore, very little is known about the precise role that the roots play in contributing to plant adaptation to hostile environments. It is assumed that while the root depth and abundance would contribute to drought tolerance, profuse rooting would enhance nutrient capture, and where the membrane transporters would exclude salts from the root cells. However, a great deal is still unknown about how these mechanisms actually operate; for example which particular characteristics of roots and root hydraulics actually contributes to water uptake in a way that confers increased tolerance, how the stress signaling from the roots affects the physiological relations in the shoot and those between the shoot and the root, how water and nutrient absorption relate to one another when both are limiting, or how roots avoid the loading of salt in xylem vessels. In this paper, our intention is not an exhaustive review of roots, but to highlight a few research topics related to abiotic stresses - mostly drought stress, but also nutrient limitation (especially phosphorus) and salt stress - where roots and their hydraulics are at the center stage. First, we provide an update on root structure, root hydraulics, and modes of water and nutrient absorption, mainly focusing on how inter- and intra-specific variations in these aspects can modify the way roots respond to a range of abiotic stresses. We then review scattered reports across a range of crops showing the contribution of roots to stress tolerance, and then report our own assessment of the role of roots using near isogenic lines (NILs