Growth and development of roots of grapevine (Vitis vinifera L.) in relation to water uptake from soil

Developmental patterns of lateral roots and their vascular differentiation were investigated for Vitis vinifera L. cv. Shiraz to assess the likely contribution of lateral roots to total water uptake of plants subjected to different irrigation regimes. Correlation analyses showed a significant positive correlation between main root diameter and the diameter of first order lateral roots of well-watered plants, but in water-stressed plants the two were not significantly correlated. The correlations between diameters of first order lateral roots and the diameters of main roots were greater than correlations between the lengths of first order laterals and the diameters of main roots. The suberised surface area of well-watered main roots increased from 4% of total surface area at 0.25 cm to 100% at 10 cm from the tip, whereas that of stressed plants increased from 15% at 0.25 cm to 100% at 5 cm from the tip. In all treatments the highest linear density of first order laterals was about 7 laterals cm(-1) of main root. More than 50% of first order laterals had diameters less than 0.05 cm, and more than 90% of them had lengths less than 5 cm. Calculations of axial resistances based on xylem diameter measurements suggest that the axial resistances of root segments may not be uniform along roots as is often assumed in models of water uptake. Water flow into the main roots via the lateral root pathway is likely to be much smaller than that via the direct radial flow pathway as only about 1 % of surface area of main roots is directly occupied by lateral roots, leaving the other 99 % of main root surface area available for the direct radial flow pathway.