ABSTRACT
Soil is an extremely complex growth medium with enormous biodiversity and wide variation in mineral and organic matter compositions. Soil provides plants with water, nutrients, and a secure anchorage, but may also restrict root growth
in unfavorable physical or chemical conditions, as roots are the underground structure of plants directly in contact with soils. Plant roots exhibit various adaptive responses to soil stresses. They are the first to encounter stress factors in the soil and thus are potentially the first sites of damage or the first lines of defense in the plants exposed to soil stress. Abiotic stresses of the soil include the availability of water and oxygen, high mechanical resistance, heavy metal toxicities, nutrient deficiencies, and salinity toxicity around roots. A better understanding of the mechanisms of root morphological, physiological, and molecular responses would expand our understanding of whole plant responses to abiotic stresses. In this chapter, we review recent research on morphological, physiological, and cellular responses of roots to major soil abiotic stresses, including water (drought, submergence), compaction, and salinity stresses.
