Geoscience Reference
In-Depth Information
absorption of nutrients. Further back, typically about 2-5 cm from the tip, branches
appear. These grow out from the deeper tissues of the root, at first at right angles to
the parent, but then changing angle progressively as they get further from its influen-
ce. These branches may themselves eventually produce branches, and they likewise,
until the whole complex branching pattern of a mature root system is produced.
FIG. 14
Branching root system of young spruce tree
Picea
and adventitious roots of arrowhead
Sagittaria sagitti-
folia.
(From Livingston 1922.)
The overall structure or architecture of a root system is very variable, depending
upon soil conditions, such as wetness and fertility, because it results from myriads of
responses of individual root tips to the local conditions. For example, branches may
be produced more profusely where roots grow through patches of soil which are espe-
cially rich in nutrients, perhaps because of a decaying carcass or a fertilizer granule,
and these branches grow more rapidly, so producing more branches themselves; in
addition, the angle of branching may change. Interestingly, it seems that only plants
of more fertile habitats, which might encounter such 'hot-spots' frequently, show this
response well; plants from poor soils seem to be less able to respond.
In an annual plant, little more happens to the root system before it dies when the
plant itself seeds and dies. An annual plant's root system performs two main func-