300
H. WALTER AND E. STADELMANN
Two different types of halophytes can be clearly distinguished from Fig.
37:
1. The chloride halophytes having ash with low sulfate content which
may in part originate from organic compounds.
2. The sulfate halophytes, characterized by a sulfate content which in
most cases exceeds the chloride content of the ash.
The salt content is given in Figs. 37 and 38 in percent of the ash. An
indication in equivalents would be more accurate; however, such recalculation would not significantly change the graphic presentation in Figs. 37
and 38. The S0 4
2
~ bars would become shorter relative to the Cl~ bars,
and the K 2 0 bars would be shorter with regard to the Na 2 0 bars. The
Na.O bars remain about the same.
The graph indicates in addition a third type of halophyte: one which
contains much higher equivalents of cations (Na
+
and K
+
) than of inorganic
anions (C\~ and S 0 4
2
) . This group consists of plants which may be called
alkaline halophytes. Anabasis aphylla, a chloride halophyte, could also
be classified as an alkaline halophyte (Fig. 37). During ashing (but also
in the normal decomposition of these halophytes in their habitat) the sodium ion combines with C0 3
2 _
(formed in the burning process of organic
material) to form soda. These species, therefore, cause soda enrichment
of soil. In the intact plants, the Na
+
ions are neutralized by the organic
anions (often oxalic) of the cell sap. Since the content of organic anions
is greater than the Na
+
content, the cell sap has a low pH.
A fourth group consists of desalting halophytes. These plants excrete
salts (mainly NaCl) through special organs, the salt glands. Desalting halophytes contain considerably less Na
+
and C\~ in their total dry matter
than nondesalting halophytes, and are nonsucculent (Fig. 37). The only
exception is Avicennia which has a Cl~ content of over 50% in the ash
and hence some degree of leaf succulence. In the cell sap about 87% of
the Cl
-
ions are neutralized by Na
+
and only 5.8% by K
+
(Scholander
etal, 1962, p. 723).
The expressed sap of glycophytes (nonhalophytes) has an ash content
of less than 10% of the total dry matter (for grasses, the Si0 2 content
is not considered here) and the ash contains much more potassium than
Na
+
and Cl~ (Fig. 38).
The regulation of salt concentration of leaves of halophytes is still little
understood. For halophytic land plants this concentration is related to salt
concentration of soil (see p. 288ff). Some details about regulation of leaf
salt concentration are known for mangrove plants. Their xylem sap was
found to have a rather low salt concentration. Even in the desalting species,
Avicennia, the NaCl concentration of xylem sap is only 0.2-0.5% and in
H. WALTER AND E. STADELMANN
Two different types of halophytes can be clearly distinguished from Fig.
37:
1. The chloride halophytes having ash with low sulfate content which
may in part originate from organic compounds.
2. The sulfate halophytes, characterized by a sulfate content which in
most cases exceeds the chloride content of the ash.
The salt content is given in Figs. 37 and 38 in percent of the ash. An
indication in equivalents would be more accurate; however, such recalculation would not significantly change the graphic presentation in Figs. 37
and 38. The S0 4
2
~ bars would become shorter relative to the Cl~ bars,
and the K 2 0 bars would be shorter with regard to the Na 2 0 bars. The
Na.O bars remain about the same.
The graph indicates in addition a third type of halophyte: one which
contains much higher equivalents of cations (Na
+
and K
+
) than of inorganic
anions (C\~ and S 0 4
2
) . This group consists of plants which may be called
alkaline halophytes. Anabasis aphylla, a chloride halophyte, could also
be classified as an alkaline halophyte (Fig. 37). During ashing (but also
in the normal decomposition of these halophytes in their habitat) the sodium ion combines with C0 3
2 _
(formed in the burning process of organic
material) to form soda. These species, therefore, cause soda enrichment
of soil. In the intact plants, the Na
+
ions are neutralized by the organic
anions (often oxalic) of the cell sap. Since the content of organic anions
is greater than the Na
+
content, the cell sap has a low pH.
A fourth group consists of desalting halophytes. These plants excrete
salts (mainly NaCl) through special organs, the salt glands. Desalting halophytes contain considerably less Na
+
and C\~ in their total dry matter
than nondesalting halophytes, and are nonsucculent (Fig. 37). The only
exception is Avicennia which has a Cl~ content of over 50% in the ash
and hence some degree of leaf succulence. In the cell sap about 87% of
the Cl
-
ions are neutralized by Na
+
and only 5.8% by K
+
(Scholander
etal, 1962, p. 723).
The expressed sap of glycophytes (nonhalophytes) has an ash content
of less than 10% of the total dry matter (for grasses, the Si0 2 content
is not considered here) and the ash contains much more potassium than
Na
+
and Cl~ (Fig. 38).
The regulation of salt concentration of leaves of halophytes is still little
understood. For halophytic land plants this concentration is related to salt
concentration of soil (see p. 288ff). Some details about regulation of leaf
salt concentration are known for mangrove plants. Their xylem sap was
found to have a rather low salt concentration. Even in the desalting species,
Avicennia, the NaCl concentration of xylem sap is only 0.2-0.5% and in