In this experiment I decided to use the following plants, which seem to be good representatives of different ecotype groups:

Hard-water species

Soft-water species

Lights

Filtration

Temperature

Substrate

Note on pH

• I'll try to keep the pH about the same everywhere (around 5).
• To achieve this, I will not use any bicarbonates (HCO₃⁻) in the recipes, so there will be virtually zero alkalinity (KH = 0). This way the initial pH should be around 5.5. With the addition of 10 ppm CO₂, it should drop to 5.
• For pH control I will use either bicarbonates (to increase pH) or hydroxides (to decrease pH).

Note on the unsuitability of using flowering plants → The Alternanthera case

Why not use flowering plants in experiments

One of the plants I used in this experiment was Alternanthera reineckii ‘Mini’, which [unfortunately] was in bloom at the time. As it turned out, using flowering plants was not a good idea. Why?

Flowering plants redirect energy to reproduction—developing flowers, seeds, etc. This means less resources for growth and adaptation. When submerged, plants need to adjust morphologically and physiologically, like growing submerged-type leaves. Flowering plants might lack the energy for this, causing delays. The presence of apical flowers halts terminal growth. In some plants the tip is occupied by a flower, so the main stem can't grow new leaves. Instead, they have to rely on axillary buds at internodes, which takes more time and energy to activate. Flowering also involves hormones like gibberellins and auxins focused on reproduction, which might suppress growth-promoting hormones needed for new leaf development. Submergence stress adds ethylene buildup, further complicating things for flowering plants.

This problem affected A. reineckii to such an extent that it made no sense to continue with it in the experiment, because even if it had eventually succeeded in transitioning from the emersed to the submerged form, the differences in growth (and the survival rate of individual leaves) between the individual aquariums were so significant that it would not be possible to determine what was due to the recipe used and what was due to the difficulties of this demanding transition. In addition, these plants (or rather their old dying leaves) have become a significant source of algae.

Algae infestation

Therefore, I decided to remove this plant species from the experiment.

Carbon Dioxide (CO₂)

Week #1 (day #6)

#1

pH 4.3

#2

pH 6.1

#3

pH 4.3

#4

pH 4.3

#5

pH 6.1

#6

pH 4.3

• All plants arrived in excellent condition, except for Alternanthera

Week #2-4

#1

pH 4.3

#2

pH 6.1

#3

pH 4.3

#1

pH 4.3

#2

pH 6.1

#3

pH 4.3

#4

pH 4.3

#5

pH 6.1

#6

pH 4.3

#4

pH 4.3

#5

pH 6.1

#6

pH 4.3

Week #5 (day #32)

#4

pH 4.3

#5

pH 6.1

#6

pH 4.3

Details  

Hygrophila in aquarium #1

• Subjectively in the best condition, beautifully straight leaves, nice/rich coloration
• The most vigorous root system with a series of long, fine hairs pointing straight up

#1

#1

#1

Hygrophila in aquarium #2

• Similar condition as in aquarium #1, but some leaves are slightly deformed or wavy
• The coloration of the leaves seems to be less rich (paler) here

#2

#2

Hygrophila in aquarium #3

• The largest biomass, but also the most deformed leaves (wavy, twisted)
• Interestingly, the root system here lacks the fine, long hairs pointing straight up

#3

#3

#3

Ammannia & Rotala in aquarium #4

• The growth tips of Ammannia and Rotala are slightly deformed (stunted)
• The root system of Ammannia and Rotala is very poor
• The lower leaves of Ammannia often turn brown (interestingly, it is usually the left (or right) half of the leaf that turns brown first, while the other half remains normal) and tend to be greener
• Rotala growth tips appear paler (more pinkish)

#4

#4

#4

#4

#4

#4

#4

#4

#4

Rotala's trimming & replanting

#4

#4

#4

Ammannia & Rotala in aquarium #5

• The growth tips of Ammannia and Rotala are slightly deformed (stunted)
• The root system of Ammannia and Rotala is very poor
• The lower leaves of Ammannia often turn brown (interestingly, it is usually the left (or right) half of the leaf that turns brown first, while the other half remains normal) and tend to be greener
• Rotala growth tips appear paler (more pinkish)

#5

#5

#5

stunting

#5

turning glassy & disintegrating

#5

#5

#5

#5

Ammannia & Rotala in aquarium #6

• Compared to aquarium #4, there are not many differences, but there is clearly more algae
• Overall, however, the plants here are in slightly worse condition (compared to aquarium #4) and appear to be somewhat smaller (especially in the case of Rotala)

#6

#6

#6

#6

#6

#6

#6

#6

Subjective assessment

Objective data

Legend:

%

ppm

State

C

N

P

K

Ca

Mg

S

Na

Cl

Fe

Mn

B

Zn

Cu

Mo

Deficiency

less than normal

Sufficiency

35-45

2-4

0.2-0.7

1-3

0.5-2.0

0.1-0.5

0.15-0.5

?

0.05-0.3

75-400

20-300

10-50

20-100

2-20

0.2-10

Excess

slightly more than normal

Toxicity

significantly more than normal

Notes:

• The ranges of deficiency, sufficiency (normal), and excess (toxicity) were taken from data applicable to terrestrial plants and adapted for aquatic plants using artificial intelligence (taking into account their physiological differences). However, I would like to point out that there is not any definitive standard (norm) for freshwater aquatic plants, so all I can offer is but a qualified estimate. I leave it up to the reader to evaluate and interpret this data in their own way.
• Where I had sufficient new material available, I used only this new material for analysis. In exceptional cases (e.g., Ammannia), I also used some of the old material (i.e., original leaves/stems). However, I never used roots.

Hygrophila corymbosa

15-20-7 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO₃:PO₄, 20 µg/ℓ Fe

• Tank 7.2: organic substrate (no P+µ in water)
• Tank 7.3: increased concentration of N+P

	%							ppm
Tank	C	N	P	K	Ca	Mg	Na	Fe	Mn	Zn	Cu
7.1	38.14	3.09	0.26	6.42	3.28	0.63	0.006	69	57	115	14.3
7.2	37.85	2.85	0.37	6.14	3.45	0.71	0.07	75	84	84	12.7
7.3	38.70	3.56	0.32	6.05	2.80	0.61	0.005	57	53	118	13.9

Ammannia pedicellata 'Gold'

2-3-1 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO₃:PO₄, 20 µg/ℓ Fe

• Tank 7.5: organic substrate (no P+µ in water)
• Tank 7.6: increased concentration of N+P

	%							ppm
Tank	C	N	P	K	Ca	Mg	Na	Fe	Mn	Zn	Cu
7.4	41.64	3.09	0.27	2.82	1.92	0.75	0.24	50	263	66	6.5
7.5	40.41	3.58	0.51	2.90	2.09	0.56	0.31	404	330	96	13.3
7.6	41.84	3.49	0.35	2.98	1.74	0.71	0.24	48	166	74	8.3

Rotala wallichii

2-3-1 mg/ℓ K:Ca:Mg, 3-0.3 mg/ℓ NO₃:PO₄, 20 µg/ℓ Fe

• Tank 7.5: organic substrate (no P+µ in water)
• Tank 7.6: increased concentration of N+P

	%							ppm
Tank	C	N	P	K	Ca	Mg	Na	Fe	Mn	Zn	Cu
7.4	40.61	2.33	0.22	3.96	1.56	0.53	0.31	38	51	29	7.9
7.5	40.58	2.94	0.64	3.50	1.38	0.52	0.76	234	105	52	8.1
7.6	40.95	2.79	0.36	3.53	1.44	0.52	0.25	41	50	36	11.8

The main problem in this experiment seems to be too low iron concentration in aquariums with inert substrate on one side and too high microelement concentration in aquariums with organic substrate on the other side (accompanied in the first set by excessively high concentrations of metal cations K-Ca-Mg).

Potassium (K)

• Observed pattern: Higher K input → higher tissue K (strong correlation)
  • An external concentration of 15 mg/L K resulted in a dramatically increased potassium content in dry matter => above 6% K. This is expected as potassium is highly mobile and readily taken up when available.

Calcium (Ca)

• Observed pattern: Higher Ca input → higher tissue Ca (weaker correlation)
  • However, compared to potassium, this correlation is not as significant => while at an external concentration of 20 mg/L Ca, the internal concentration was 2.8-3.5%, at an external concentration of 3 mg/L Ca, the internal concentration was 1.7-2.1%, which still seems more than sufficient.

Magnesium (Mg)

• Observed pattern: Internal Mg concentration does not seem to depend too much on its external concentration
  • It seems to make no difference whether you add 1 or 7 mg/L Mg to the water => the result appears to be the same.

Phosphorus (P)

• Observed pattern: [Fresh] organic substrate is able to cover all plant requirements for P + concentration of 0.3 mg/L PO4 seems to be sufficient for plants
  • In aquariums 7.2 and 7.5, phosphorus was completely omitted, but according to laboratory analysis, the plants from these and other aquariums contained roughly the same amount of phosphorus (in aquariums with substrate, even slightly more).

Nitrogen (N)

• A concentration of 3 mg/L NO3 appears to be more than sufficient for plants [under the given conditions]. Nitrogen also appears to be highly mobile, so higher external concentrations usually lead to higher internal concentrations, but it is difficult to overfertilize with nitrogen (similar to calcium). There seems to be no point in going higher [again "under the given conditions"!].

Microelements

1. A concentration of 20 µg/L Fe seems to be insufficient [under the given conditions].
2. The concentrations of other microelements seem to be sufficient.
3. A correlation between higher internal zinc concentrations and higher potassium concentrations in water is unlikely. A possible explanation could be enhanced root activity or membrane permeability due to higher K levels.

Organic substrate

• Fresh organic substrate seems risky to me, as in most of my experiments it led to increased or downright toxic levels of several microelements in plant tissue.