The proteoid roots of Hakea prostrata and H. laurina are concentrated in the
surface soil horizons, even though the root systems penetrate to much greater depths.
The relationships of a number of soil and plant factors to proteoid root occurrence
in a given portion of the root system were examined. Pockets of humus-rich soil in
any part of the root system greatly increased the proteoid root concentration in that
region. The following factors, listed in their apparent order of importance, were analysed:
local concentration of parent roots, local level of soil organic matter, local
nitrogen availability, shoot growth, nitrogen concentration of the shoots, vertical
distance of the region from the soil surface, local availability of calcium, magnesium,
and potassium, local bulk density and certain other physical factors, nutrient status of
the rest of the root system, horizontal distance of the region from the centre of the
plant, relative maturity of parent roots in the region, and local soil pH and certain
other chemical factors.
The nitrogen component of soil regions high in organic matter largely accounted
for their higher non-proteoid root concentration, smaller proteoid root size, greater
number of laterals, and longer roots per unit weight, but not their much greater number
of proteoid roots per unit total root weight. This suggests that other factors are also
involved in proteoid root formation.
Morphological Characterization of Root System Architecture in Diverse Tomato Genotypes during Early Growth