Rooting, Water Uptake, and Xylem Structure Adaptation to Drought of Two Sorghum Cultivars

Abstract

Several mechanisms have been proposed to explain the high tolerance of sorghum [Sorghum bicolor (L.) Moench] to drought. This paper reports a field study on the effects of soil moisture stress on the rooting habits, transpiration rate, and xylem anatomy of two sorghum cultivars, Tabat (drought susceptible) and Gadambalia (drought tolerant). Two levels of water stress, −0.02 MPa (wet) −0.75 MPa (dry), were applied. Tabat had a higher root length density (RLD), higher late metaxylem (LMX) vessels per nodal root, higher leaf area, and higher transpiration rate than Gadambalia. In Tabat, soil moisture stress reduced RLD by 30%, nodal roots by 31%, number of LMXve ssels in the root by 42%, leaf area by 13%, and transpiration rate by 11%. In Gadambalias oil moisture stress did not affect RLD at depths >‐0.2 m, numbero f nodal roots, or numbero f LMXve ssels per nodal root. However, leaf area and transpiration rate were reduced by 3 and 11%, respectively. Under dry conditions, Gadambaliad isplayed a higher water extraction efficiency than Tabat throughout the profile (0‐0.9 m). In Gadambaliau, nlike Tabat, the stem was highly sclerified. A 1‐ to 3‐cell‐thick layer of schlerenchymaw as observed beneath the epidermis. The peripheral vascular bundles were surrounded with a 3‐ to 6‐ceil‐thick schlerenchyma sheath. However, in roots anatomical differences were less prominent. Drought tolerance in Gadambaliias associated with higher water extraction efficiency, fewer nodal roots per plant, fewer LMXv essels per nodal root, a smaller leaf area, and a well developed sclerenchyma.