In the Karoo of South Africa, do plants with succulent fruits have foliage rich in potassium relative to nitrogen?

(writing in progress)

I have observed that succulent fruit-pulp is rich in potassium relative to other nutrients (https://www.inaturalist.org/journal/milewski/72763-why-are-fleshy-fruits-rich-in-potassium# and https://www.inaturalist.org/journal/milewski/63113-why-are-lauraceous-fleshy-fruits-potassium-rich-despite-being-non-succulent#).

If so, do plants with succulent fruits have foliage unusually rich in potassium relative to nitrogen?

I have previously found that plants with fleshy fruits have foliar concentrations of: potassium >1.9
%, nitrogen >1.5%.

ratios of potassium/nitrogen

In this Post, I test this by reviewing the values reported in the literature, for the Karoo (https://en.wikipedia.org/wiki/Karoo) in South Africa.

My finding is that the answer is no. This is perhaps partly because plants with succulent fruits in the Karoo are rich in nitrogen, relative to other ecosystems.

Then following is a summary of the mean percentages (concentration on a dry matter basis), by categories. In each case the numerator refers to potassium, and the denominator refers to nitrogen.

PLANTS WITH SUCCULENT FRUITS 1.7/2.4
GRASSES 1.0/1.3
SUCCULENTS 2.05/1.8
DAISIES 1.5/1.0
LEGUMES 1.0/2.2

My commentary:
Plants with succulent fruits, of which Lycium is an example, have foliage that is rather rich in potassium. However, the corresponding concentrations of nitrogen are also rather great. Thus, the ratio of potassium to nitrogen remains modest.

Asteraceae in Karoo:

98 samples

Crude protein mean 9.58%
Nitrogen mean 1.53%
Potassium mean 1.52%
Potassium/nitrogen ratio 0.99

Legumes in Karoo

6 samples

Crude protein mean 13.73%
Nitrogen mean 2.2%
Potassium mean 0.96%
Potassium/nitrogen ratio 0.44

Grasses in Karoo

49 samples

Crude protein mean 7.826%
Nitrogen mean 1.252%
Potassium mean 0.9844% (range 0.14-3.79%)
Potassium/nitrogen ratio 0.786

DISCUSSION

In Karoo vegetation, potassium/nitrogen ratios are succulent foliage > daisies > grasses and plants with succulent fruits > legumes.

It is remarkable that virtually no legume has a succulent has succulent foliage or fruits, and part of the explanation may be the limited ration of potassium to nitrogen in legumes. This also holds for nitrogen-fixing plants generally.

Daisies seem to be poor in protein, possibly even more so than grasses. This may help to explain

• their general unpalatability to browsers, and
• their acceptability as bulk food to Merino sheep, which are basically grazers.

However, they are certainly not poor in potassium. The concentrations of potassium in the leaves of daisies in Karoo vegetation are consistent with the textures of the foliage.

INTERCONTINENTAL COMPARISONS OF SHARED GENERA

LYCIUM

Lycium is a protein- and potassium-rich non-legume.

It is rich in potassium compared to most coexisting plants other than succulents (which average slightly more than 2%) in the Karoo, with values double those in coexisting grasses and legumes. This is consistent with the fleshiness (semi-succulence) of the leaves.

However, the ratio of potassium to nitrogen is small in Lycium, because of its richness in nitrogen.

Foliar concentrations of potassium are slightly less than 2% in the Karoo, compared to about 2% in Australia, and 3-6% in the USA. The latter values seem remarkably great in absolute terms.

In the Karoo, foliar nitrogen, even when underestimated by analysis for crude protein, is 2.8% in Lycium. This is somewhat greater than expected for an intercontinental genus of base-rich soils under semi-arid climates. It exceeds the means for the following categories of plants in the Karoo:

• plants with succulent fruits (2.4%),
• legumes (2.2%),
• succulents (1.8%),
• grasses (1.3%), and
• daisies (1.0%).

ATRIPLEX

Atriplex seems typical of succulent plants in its ratio of potassium to nitrogen

Publicado el 10 de julio de 2023 a las 06:28 AM por milewski