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Reprinted from the Botanical Gazette 45: 11 7-1 24, Febniar 1908

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THE ANTAGONISTIC ACTION OF MAGNESIUM AND

POTASSIUM

W. J. V. OSTERHOTJT

(with three figures)

It has been previously pointed out^ that potassium may inhibit
more or less fully the poisonous effects of magnesium and that the
abundance of potassium in the soil makes this inhibitory action of
importance in soil investigations. Loew and Aso^ have criticized
this statement. Their objections are that only chlorids were used
and that no flowering plants were investigated. In the present paper
these objections are fully met. The experiments extend over a wide
range of forms and their general agreement furnishes conclusive proof
of the above-mentioned action of potassium.

The technique employed has already been described in previous
papers in this journal.^ The material was placed in glass dishes con-
taining 100-300'^'^ of the solution and was covered with glass plates to
exclude dust and hinder evaporation. Water twice distilled and salts
which were tested for purity were used throughout. The results given
in the tables are in all cases averages of several series of experiments.

The first experiments were made upon a marine alga, Entero-
morpha Hopkirkii, which is able to live in both sea water and dis-
tilled water. It was taken from the sea water, rinsed in distilled
water, and placed directly in the solutions. The solutions used were
of the concentration 0.37 5 w, which has the same osmotic pressure
as the sea water in which the plants naturally grow.

In pure MgCl^ .0375 w they lived but four days; in pure KCl .0375 w
seven days; while in distilled water and sea water they were alive
and vigorous at the end of twenty days when the experiment was dis-
continued. It is evident therefore that both KCl and MgCl^ have a
poisonous action.

This poisonous effect largely disappears if we mix the two salts

I OsTERHouT, University of California Publications, Botany 2:235. 1906.
' Loew and Aso, Bull. Imp. Coll. Agr. Tokyo 7:395. 1907.

3 OSTERHOUT, Box. GAZETTE 42:127-134. 1906; 44:259-272. 1907.

117] [Botanical Gazette, vol. 45

272648

ii8

BOTANICAL GAZETTE

[FEBRUARY

(MgClj and KCl) in proper proportions. In the mixture 100*=*= MgCl,
+40*^*^ KCl, the plants were alive and in good condition at the end of
twenty days, when the experiment was discontinued. It is evident
therefore that in the mixture of magnesium and potassium chlorids
the plants live five times as long as in pure magnesium chlorid and
three times as long as in pure potassium chlorid.

TABLE I

Marine Algae

All quantities given are cubic centimeters of o . 37SW solutions

Coltuie solution

KCl

100 KCl I

40 MgCla S

MgCl,

Distilled water

Sea water (total salts = 2. 7 per cent.)
Artificial sea water (total salts =
2.7 per cent.):
100 NaCl \

7.8MgCU /

a.SMgSO^J

2.2 KCl 1
I CaCla '

Duration of life in

days: Entero-
tnorpha Hopkirkii

7
20 +

20+
20+

20+

The plus agn indicates that the plants were ali\-e at the end of the experiment.

The results obtained from the study of Vaucheria were even more
striking. Zoospores were allowed to attach themselves to slides.
These were then rinsed in distilled water and placed in the solutions.
The results are shown in the following table and also in ^^. i.

TABLE II
Fresh-water Algae
All quantities given are cubic centimeters of .oiw solutions

i9o8] OSTERHOUT— ACTION OF MAGNESIUM AND POTASSIUM iig

A large Spirogyra of the majuscula type was used for experiments
with the stronger solutions. The results are given in Table III.

TABLE III

Fresh-water Algae

All quantities given are cubic centimeters of .0937W

solutions

Culture solution

Duration of life in days:
Spirogyra species

KCl

100 KCl I

40 MgCla S

MgCla

25 +

Distilled water

The plus sign indicates that the plants were alive at the end of the
experiment.

A series of experiments was next made with
the gemmae of Lunularia. These were allowed
to float on the surface of the solutions. A
large number was used and the average results
given in the following table.

TABLE IV

Liverworts

All quantities given are cubic centimeters of .0937W

solutions

Culture solution

Duration of life

in days:

genunae of Lunularia

KCl

100 KCl )

120 +

so MgCl, )

100 KCl I

120 +

100 MgCla S

50 KCl )

100 MgClj )

MgCU

Distilled water

<?.

The plus sign indicates that the plants were alive at the end of the
experiment.

Fig. I. — Growth
of Vaucheria during
45 days in . 01m solu-
tions. I, KCl, gain
o; 2, ioqcc KCl
-I-40CC MgClj, gain
4200%; 3, MgCla,
gain o. X 25.

I20

BOTANICAL GAZETTE

[FEBRUARY

It will be noticed even when magnesium greatly preponderates in
the mixed solutions the plants live twenty-five times as long as in pure
MgClj, and over eight times as long as in pure KCl. Increasing the
proportion of potassium increases the length of life.

The same relation is seen more completely in the next table (Table
V). Decreasing the amount of Mg causes increased growth up to a
certain point (loo K + io Mg). StUl further decrease of the relative
amount of Mg beyond this point is imfavorable. The optimum
relation is therefore not far from lo Mg + loo K.

TABLE V

Liverworts

All quantities given axe cubic centimeters of .037SW solutions

CUVrtTKE SOLUTION

KCl

100 KCl )

5MgCla5

100 KCl I
10 MgCla S

100 KCl I
25MgClJ

MgCU

Distilled water

Growth in 150 days: geioiae
of lunulakia

Length of
thallus

0-5
3-3°

3-41

2.6

o-S
6.60

Percentage of

gain in length

of thallus

O
560

582

420

It will be noticed also that the gemmae made no growth whatever
in pure MgClj or pure KCl, while in mixtures of the two a good growth
occurred.

For the study of flowering plants wheat was chosen. The seeds
were supported in the solutions on strips of filter paper as described
in a previous paper.'* The results agree with those already given.
Table VI shows that certain mixtures of potassium chlorid and mag-
nesium chlorid are much more favorable than cither of the pure salts
(see also figs. 2, j).

4 0STERH0TJT, BOT. GAZETTE 44:259-272. 1907.

i9o8] OSTERHOUT— ACTION OF MAGNESIUM AND POTASSIUM 12 1

Turning now to the experiments with sulfates and nitrates, we
see entirely similar results, save that the mixed solutions, while better
than pure magnesium salts,
are not better than pure potas-
sium salts. The question
might then arise whether the
favorable result is due in this
case to mere dilution of mag-
nesium salts with less poison-
ous ones. This, however, is
not the case. We are dealing
with a true antagonistic action.
This is shown by the fact that
addition of the potassium salt
in solid form likewise pro-
duces a favorable result, and
also by the fact that the
addition of pure water does
not produce anything like
the improvement seen on the addition of the same amount of a
solution of a potassium salt.

.0937 m

Fig. 2. — Growth of wheat roots during
40 days in .og^ym solutions: I, MgClj,
aggregate length of roots io""n; 2, loocc
KCl + 2SCC MgClj, aggregate length of roots
153™™; 3, KCl, aggregate length of roots
no™™. X§.

.05 m-

,037&m

a bed

Fig. 3. — Curves showing growth of wheat roots in salt solutions. The ordinates
represent concentrations (parts molecular); the abscissae represent the aggregate
length of roots per plant in millimeters, a, loocc KCl+ioocc MgCU; 6, loocc KCl
+ SOCC MgClj; c, KCl; d, ioqcc KCI + 25CC MgClj.

122

BOTANICAL GAZETTE

TABLE VI
Wheat

[FEBRUARY

Culture solution

Growth during 60 days
aggregate length of roots per plant dj lof .

In .og37w solutions

In .05 m solutions

In .o3^sm solutions

KCl

no
66

153

36
48
60

114

32
80

268
170

224

312

216

112

148

166
10

275
76

144

224
8

340

loo KCl )

loo MgCU )

loo KCl \

294

388
28

50 MgCla S

100 KCl \

25 MgCl, 5

MgClj

SO K,S04 I

276

144

190

240
24

50 H,0 S

5oK,S04 )

100 Mgso^ 5

5oK,S04 )

SO MgS04 )

SoKjS04 I

25 MgS04 5

MgSO.

KNO,

345
104

100 KNO3 )

100 MgCNOj), J

100 KNO3 )

198

290

5oMg(N03),5

100 KNO3 I

2sMg(N03),i

MeOSIO,),

Distilled water

lAO

Since each molecule of K,S04 yields two K ions, half as much K.SO^ is used as KCl or KNO, .
The figures for 50 K.SO4+S0 H.O are comparable with the corresponding figures for KCl and KNOj,
though the concentration of the solution is only half as great. For example, the roots reach a length
of 8o""» in so« K,S04 .o937»» + soee H.O; a length of 216"" in 50" K,S04 .osw + so" H.O; and
a length of 276"™ in 50" KaS04 .037sm+so« H.O.

It will be noticed that these antagonistic effects are less marked as
the concentration is lowered. This is of course true of all antago-
nistic action, since as the concentration is lowered toxicity diminishes
and the effect of its inhibition is consequently less striking.

It is observed that those parts which are in direct contact with
solutions always show their effects much more plainly than those

1908] OSTERHOUT— ACTION OF MAGNESIUM AND POTASSIUM 123

(e. g., leaves and stems) which are raised above them. It seemed
desirable therefore to find out how sections of stems and roots would
behave in the solutions. The answer to this question is given in
Table VII. Transverse sections of the stem of Tradescantia and the
root of the common red beet were employed. They were cut on a
microtome and were of considerable but uniform thickness.

TABLE VII

Cuttings and Sections
All quantities given are cubic centimeters of .o937ffi solutions

Culture solution

Duration of life in days

Microtome sections

of stem of
Tropaeolum majus

Microtome sections

of root of

Beta vulgaris

Develophent

Cuttings IS'"

long of
Tradescantia

KCl

ICO KCl )
40 MgCU ) ■

MgCU

Distilled water.

28 +

20
28 +

14
27

18
28 +

No roots

Short roots

No roots
Long roots

A plus sign indicates that the plants were alive at the end of the experiment.

In both cases the color and microscopic appearance served as the
criterion of death. As is seen in Table VII, the results agree with
those already obtained. The table likewise shows the results obtained
from cuttings of Tradescantia (about 15'^™ long) which were placed
with their lower ends in the solutions.

In view of the striking agreement of results obtained from such a
variety of material, it seems useless to seek for further proof. The
experiments of Loew and Aso also show antagonism between potas-
sium and magnesium, as far as they go. They do not, however,
employ sufficient potassium (nor sufiiciently strong solutions) to bring
out the results clearly. The use of percentage solutions (rather
than molecular solutions) likewise obscures their results. More funda-
mental is their confusion of physiologically balanced solutions with
ordinary nutrient solutions.^

As for the theory of Loew and Aso that the inhibitory action of
potassium on magnesium is due to the formation of a double salt; I;

s Cf. Osterhout, On nutrient and balanced solutions. University of California.
Publications, Botany 2:317. 1907; also, BoT. Gazette 44:259-272. 1907. •* * .'.

134 BOTANICAL GAZETTE [February

need merely say that it cannot be true because this inhibitory action
is seen in mixtures of potassium nitrate and magnesium nitrate where
no double salt is formed. Moreover, even in the chlorids and sulfates
the formation of a double salt cannot much affect the result, since the
double salt, at the concentrations here used, dissociates and sets free
magnesium and potassium ions to almost the same extent as the
simple salts.

RESULTS

Magnesium salts and potassium salts, used separately, are poison-
ous to plants, but when mixed together (in suitable proportions) the
poisonous effects more or less completely disappear. These results
are of importance in soil investigations.

• University of California
Berkeley