Morphological responses of barley roots to soil compaction and modified supply of oxygen

The morphological changes in barley roots in response to soil compaction an d hypoxia were quantified by image analysis. Based on the assumption that t hese soil stresses increase endogenous ethylene production in plants, chang es indicating higher construction costs for roots, such as decreased specif ic root length, were expected. The hypothesis was found to be only partly c orrect. Most morphological changes of barley roots were probably a reaction to increased soil mechanical impedance. Examples of this are root width, w hich was increased by compaction apart from in wet soil, as well as increas ed width and specific volume, and a decreased specific length of roots in t he deepest layer of well-aerated loose soil. However, in loose moist soil h ypoxia prevented root growth, but did not change root morphology. The resul ts suggest that severe hypoxia lessens the possibilities of roots to adapt to the hypoxic soil by reducing root growth and by preventing the formation of aerenchyma.