Sensitivity of root and leaf water status in maize (Zea mays) subjected to mild soil dryness

Abstract

The aim of this work was to test the sensitivity of the water potential (Ψ_w), osmotic potential (Ψ_s) and turgor (Ψ_p) of roots and leaves of maize seedlings (Zea mays L. cv. Carla) subjected to a mild stress in drying soil in a growth chamber. To the best of our knowledge there are no experimental data which describes diurnal courses of Ψ_w in soil, roots, and leaves and the parallel changes in the osmotic potential (Ψ_s) and turgor (Ψ_p) of roots and leaves from plants grown in moist and drying soil. Root and leaf Ψ_w varied diurnally, the amplitude being much more marked in leaves than in roots. Root and leaf Ψ_w did not achieve equilibrium at predawn with the bulk soil matric potential (Ψ_m) but became higher. Our results are at variance with data indicating root Ψ_w is a sensitive indicator of soil dryness. Root Ψ_w in the well-watered and drought-stressed treatments did not differ, whereas daytime leaf Ψ_w in the droughted treatment was lower 6 days after water was withheld. Diurnal changes in Ψ_s and Ψ_p were more marked in leaves than in roots. Withholding water lowered leaf Y_p, whereas root Ψ_p substantially increased after only 3 days of withholding water. Early mild stress can be more easily and more quickly identified by changes in root Ψ_s, increases in root Ψ_p, or the divergence in root and leaf Ψ_p than by a lower Ψ_w of root or leaf. Relative water contents of roots and leaves measured in the light period indicated also sensitively falling Ψ_m.