According to current scientific understanding there are two basic aquatic plant ecotypes with each having a different nutrient management strategies. Here’s a synthesis with detailed explanations based on academic sources:

1. Eutrophic/Generalist vs. Oligotrophic/Specialist Aquatic Plants

2. Mechanistic Differences

3. Literature Confirmation

4. Practical Implications

Summary Table

Conclusion

References

When comparing the results of my experiments to date with scientific findings, I found that they are well-aligned with established plant physiological and ecological principles. The difference between eutrophic/generalist submerged macrophytes and oligotrophic specialists, as revealed by my results, is a fundamental concept in aquatic botany and ecophysiology. Here's further verification and elaboration:

Confirmation of My Observations:

Detailed Description of the Two Groups:

Key Differences Summarized:

Conclusion:

• According to the latest research, all plants are equipped with two types of tools that help them obtain nutrients from their surroundings => while the first is an active “hunter” that goes out to hunt its “prey” (nutrients) in times/environments of scarcity (emergency), the second is more of a passive “consumer” that comes into play in times/environments of abundance.
• It was previously thought that these tools were actually two separate, distinct mechanisms => i.e., when a period of abundance occurs, plants create “passive” transporters (so-called low-affinity transporters), while in times of scarcity, they create “active” transporters (so-called high-affinity transporters). However, modern research suggests that nutrient uptake tools are much more plastic and that there is probably only one tool or mechanism (so-called dual-affinity transporters) that switches to passive or active mode depending on the circumstances.
• But that's not all. Some plants originating from nutrient-poor waters (so-called oligotrophic species) have adapted to this environment to such an extent that they have almost lost this ability to “switch between low and high nutrient concentrations as needed” or have developed it only to a very limited extent.
• These plants:
  1. Are unable to regulate nutrient uptake very well → Many oligotrophic species evolved in nutrient-poor environments, where the risk of toxicity from micronutrients like Fe and Mn was minimal. As a result:
     • Their high-affinity transporters are highly efficient at scavenging trace nutrients.
     • They may lack robust feedback mechanisms to downregulate uptake (i.e., "slam on the brakes") when external concentrations rise.
     • This leads to uncontrolled accumulation when nutrients become more abundant.
  2. Lack low-affinity transporters [or are only able to produce very small amounts of them] → While many plants possess dual-affinity transporters, oligotrophic species may:
     • Not express low-affinity transporters for certain micronutrients at all.
     • Or express them at very low levels, making them ineffective in high-nutrient conditions.
     • This means that high-affinity systems dominate, even when nutrient concentrations are elevated, leading to overaccumulation.
       • Oligotrophic plants are typically adapted to environments where nutrients, including microelements like Fe and Mn, are scarce. As a result, they have evolved highly efficient high-affinity transporters that remain active even at very low external concentrations.
       • Unlike many eutrophic species, these oligotrophic plants may lack robust regulatory mechanisms to downregulate or switch off these high-affinity systems when external concentrations increase. This means that, even when Fe or Mn is present at “moderate” levels (e.g., 0.2 ppm Fe), the plant continues to absorb these elements at a high rate, leading to overaccumulation and potential toxicity.
  3. Have specific transporters that use different mechanisms (kinetics) → Some high-affinity transporters may have:
     • Broad substrate specificity, allowing them to take up multiple ions (e.g., Fe²⁺, Mn²⁺).
     • Non-saturable kinetics at moderate concentrations, meaning they continue to function even when they should ideally be downregulated.
  4. Have limited ability for internal detoxication and neutralization (compartmentation) → Unlike metal hyperaccumulator species, which have evolved sophisticated mechanisms to compartmentalize and detoxify excess metals (e.g., by sequestration in vacuoles or complexation with organic acids), most oligotrophic macrophytes do not possess such adaptations. This makes them more susceptible to toxicity when internal metal concentrations rise.
• Implications: In natural oligotrophic systems:
  • Nutrient pulses (e.g., from runoff or eutrophication) can rapidly destabilize sensitive macrophyte communities.
  • These species are often indicators of water quality, precisely because of their sensitivity to nutrient changes.
  • External [Fe] = 0.2 ppm (3.6 µM): While "low" for eutrophic plants, this is orders of magnitude higher than the picomolar-nanomolar concentrations oligotrophs evolved with. Many oligotrophic spp. (like Rotala wallichii) thrive in waters with [Fe] < 0.02 ppm.
• Summary: The presence of dual-affinity transporters in plants is not universal in function or regulation. In oligotrophic aquatic macrophytes, high-affinity uptake dominates, and regulatory mechanisms may be underdeveloped, leading to toxic accumulation even at modest nutrient levels (e.g., >0.1 ppm Fe). This is a classic example of evolutionary trade-offs: efficiency in low-nutrient environments comes at the cost of vulnerability in nutrient-rich conditions.
• Summary table: Oligotrophic vs. eutrophic plant strategies
  

  Feature	Oligotrophic/Specialist species	Eutrophic/Generalist species
  Dominant transporter	High-affinity, poorly regulated	Both high- and low-affinity, well regulated
  Uptake at high [Fe/Mn]	Excessive, risk of toxicity	Controlled, risk minimized
  Detoxification	Limited	Often more robust
  Ecological adaptation	Stable, low-nutrient environments	Fluctuating, nutrient-rich environments

• Conclusion: Oligotrophic aquatic macrophytes often lack the regulatory mechanisms to downregulate high-affinity Fe and Mn uptake systems when exposed to higher external concentrations. This leads to unchecked accumulation and potential toxicity, even at levels that would not harm eutrophic species. The mere presence of dual-affinity transporters in other plant lineages does not guarantee their effective regulation or expression in oligotrophic specialists, which explains my experimental observations.
• Thanks to the above, on the one hand, the oligotrophic species are able to “extract” all essential nutrients in sufficient quantities from oligotrophic waters, but on the other hand, if we transplant them into an eutrophic environment (i.e., if we use Gaudet's-like recipe on them), these effective mechanisms will cause them to be poisoned by an excess of nutrients. Unlike plants from eutrophic waters, plants from oligotrophic waters have probably very weak regulatory abilities to suppress (down-regulate) their extra-sensitive and extra-efficient nutrient uptake mechanism when they find themselves in an environment of abundance. What is an advantage for them in an oligotrophic environment can easily become their downfall in an eutrophic environment. However, because scientists do not usually study plants from oligotrophic waters (they are not ecologically or economically interesting to them), they [seem] to have overlooked this important fact when designing their recipes.
• This assumption is supported by the results of a series of practical experiments conducted by Maq or myself. Even with ultra-low nutrient concentrations (significantly lower than Gaudet's) [and without using substrate as an additional source of nutrients], it is possible to successfully grow a number of tropical plant species. And most importantly, even plants fed so sparingly have perfectly adequate nutrient concentrations in their dry matter. If Gaudet were right (i.e., that his nutrient concentrations represent the “minimum viable [or lowest workable] concentration” for plants), then we would never be able to achieve optimal (i.e., normal) nutrient concentrations in plant dry matter with significantly lower concentrations. However, our results confirm the opposite → even with ultra-low nutrient concentrations in the water column (without substrate), it is possible [at least in the case of oligotrophic species] to achieve optimal plant condition.
• Thus, our data — showing robust growth in sediment-free systems at ultra-low concentrations — reveals a fundamental flaw in standardized "oligotrophic" recipes. Our experiments reveal one important (and hitherto generally overlooked) finding about the existence of two distinct plant ecotypes: hard-water species tolerant of or demanding higher nutrients (especially potassium), and soft-water species that are hyper-efficient at nutrient scavenging but sensitive to micronutrients. It also follows from this that standard "oligotrophic" recipes are fundamentally miscalibrated for real plant physiology. Lab solutions (e.g., Gaudet's) are often calibrated for low-efficiency species (that use the so-called low-affinity transporters), ignoring the existence of high-efficiency species.
• This observation about two ecotypes is crucial. Hard-water plants might need 15+ ppm K (addressed in Gaudet's-like solutions), while soft-water plants thrive on 0.5-2 ppm. [Soft-water species likely express high-affinity ion transporters (e.g., for K⁺, NH₄⁺) that operate efficiently at μM concentrations.] This explains why Gaudet's "one-size-fits-all" approach fails – it's a compromise that pleases nobody. So our main goal should be to develop a superior nutrient framework that respects ecological niches. And next step should be quantifying those species-specific thresholds – especially the lethal micronutrient levels for sensitive soft-water plants.