Abstract : The research presented in this thesis investigated the functional morphology in root
systems in relation to their role in providing anchorage and stability for the plant. The
anchorage of different types of root systems was investigated as well as the influence of
several environmental factors on their development. The research presented in this study
was completed by carrying out a series of modelling, glasshouse and field experiments
using physical models and real plants.
Model experiments showed that solid shapes like bulbs are very well suited to resist
vertical upward forces, i.e. uprooting, and shed some light on the mechanism of
anchorage in bulbs. The results of this laboratory study showed that the concept of
optimal bulb shape for resisting uprooting is viable. Uprooting tests on real bulb plants
confirmed the theoretical predictions about it, and showed the importance of bulbs in
anchorage. This study also proved that the soil type is very important when considering
the anchorage of solid forms such as the bulbs.
A second model study showed that the simplest models of tap root-dominated root
systems increase their resistance to overturning with the third and second power of the
embedment depth in cohesionless and in cohesive soil respectively. Anchorage strength
of a root system dominated by a tap root will be maximised with minimum investment
in structural material if the rigid tap root is extended to the largest possible depth.
Glasshouse experiments investigated the effects of soil compaction and temperature,
two of the most important environmental factors, on the axial and lateral development
and growth of the root systems of two species of young pines. It was shown that the rate
of root axial development in both investigated species decreased with an increase in soil
compaction whereas the lateral proliferation of their roots systems was not significantly
affected by soil consistency. A temperature of around 15°C seemed to be optimal for the
root elongation rate since the increase in axial length of the roots of both species was
largest at this temperature.
The effect of mechanical stimulation as a factor in shaping the root systems of plants
was also investigated. Apart from the changes caused to the parts of the tree above
ground, unidirectional periodical flexing induced an increase in total root CSA and
larger biomass allocation to the roots parallel to the plane of flexing which, in turn,
resulted in a larger number of major lateral roots with larger CSA in the plane of
Mechanical and morphological field studies on two Pinus species investigated the
anchorage of plate root systems and showed that lateral roots in older trees are not the
major source of root anchorage in either of the species; although in both species a
certain asymmetry in the distribution of major lateral root CSA was recorded, it was not
significantly correlated to the asymmetry in anchorage.