Geoscience Reference
In-Depth Information
There are two adaptive strategies (Paris-Pireyre 1988; Jacoby 1994):
Exclusion
. Plants of the
excluder
type restrict as much as possible the
penetration of salts into their tissues. More precisely, they expel to the
outside the sodium that has penetrated through exchange for K
+
or H
+
.
Thus they practise a kind of desalinization.
Compartmentalization
. Plants of the
includer
type are the most
salinity-resistant. They absorb the salts and transport them to their
aerial parts that get rid of them in two ways. They can accumulate
them in special cells located in the epidermis of the leaves. These are
salt glands
(Thomson 1975). Alternatively, they accumulate the salts in
large vacuoles that occupy 90 per cent of the volume of the cell. This
provokes a call for water by osmosis. These plants are gorged with saline
water and are called
succulents
(e.g.,
Salicornia fruticosa
). This mechanism
ensures their turgor in a situation where the osmotic pressure of the
external solution could lead to their wilting. Therefore, in a way, they
create a pressure equilibrium.
In actual fact, the two strategies can coexist in certain species.
At conductivity higher than 16 mmhos/cm, we only see specialized
plants. For example, on the Mediterranean coast:
Arthrocnemum glaucum
,
Statice limonium
,
Salicornia fruticosa
,
Obione
portulacoides
,
Sueda maritima
, etc. (Fig. 13.17).
Defensive strategies of plants
Fig. 13.17
Plant formation with
Salicornia fruticosa
in the Camargue (France). The soil sur-
face is cracked (prisms) and partially covered with salts.
Photo
: author.
When the salinity is very high nothing grows.
In Chad, the characteristic plant formation of saline soils (solodized
Solonetz) is an arbustive steppe with irregularly scattered thorny plants
(Bocquier 1964). It has very limited pastoral value and is useful only
for transhumance cattle.
