Interested to hear people's views on how providing unlimited nutrients helps control algae?

[sWozzAres]

· Plants produce substances that limit algae growth (allelopathy).

Actually the opposite is true, plants are known to produce hormones that stimulate spore germination in some algae.

Plant hormones such as indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), naphthalene-2-acetic acid (NAA), gibberellic acid (GA3), kinetin, and tryptophan (a precusor of IAA) at certain levels (either individually or in combination) stimulated SG in some algae (Table IV; p. 288). They probably promote cell enlargement, cell division or have some other cellular and molecular effects.

Factors affecting spore germination in algae — review
http://link.springer.com/article/10.1007/s12223-009-0047-0

 

[alto]

Unfortunately I cant read this review (no open access) & can't seem to find the magic word series for Google to list related articles in the first few result pages
- are these substances actually released into the surrounding aquatic environment? or is this a series of extracted compounds applied to the algal spores & effects observed?

Just to get this slightly on topic

providing unlimited nutrients helps control algae?

in some of the papers I linked, reduced levels of phosphate & (nitrates? guilty of skimming ) were also observed in the "algae-free zone" surrounding the plant mass, & this nutrient "deprivation" was considered a factor in algal limitation

(or perhaps this detail was included in some of the papers I neglected to link - there are many, many examples of allelopathy, published in various journals, authored in many countries ...
ie not some research group's pet project)

 

[691175002]

I think the main evidence that allelopathy is not dominant in aquariums is that if plants were secreting chemicals that inhibited algae, performing a water change should dilute these chemicals and immediately result in an algae bloom.

I'm sure that healthy plants are able to defend themselves against algae, but tying it to a specific mechanism is hard because there are so many contradictory examples.

If you consider algae as a population that goes through booms and busts; keeping it suppressed by reducing areas for it to reproduce (healthy plants), limiting its main source of food (ammonia? organics?), and culling whenever possible (cleanup crew, manual removal), should ensure that algae cannot get a foothold in the tank.

This seems pretty consistent with my experience.

 

[alto]

I think the main evidence that allelopathy is not dominant in aquariums is that if plants were secreting chemicals that inhibited algae, performing a water change should dilute these chemicals and immediately result in an algae bloom.

You're expecting grand gestures from a microscopic (picoscopic?) process

 

[Soilwork]

Is it really a question of plants defending themselves, algae invading, lying in wait, waiting to attack, scavenging, looking for weakness etc etc. Yes the goal of organisms is to survive but why? Is there a bigger picture? Plants and algae have the same purpose no? To support life on Earth. Whatever the mechanism is that induces/suppresses algae perhaps they are working together to support an ecosystem? If algae can live as spores for such a long time then why not allow higher plants to carry the torch? Plants carry food, provide shelter, spawning sites, materials and provide massive amounts of oxygen. If the plants can no longer do this then the ecosystem is in peril. Plants are decaying and sending out signals to the algae. The algae mearly begin to take over the role of supporting the ecosystem. They use food the plant releases to Gain a foothold. They use leaves for this and to get closer to the light. The plants are dying fast and the algae need to spread quickly to keep the system alive. Algae take over. Then when the conditions become right again for plants they grow once more, the ecosystem is safe and algae resides back in wait just in case they are called in to action again.

This is how I like to look at it. It stops me from swearing when I'm scraping the GSA off the back of my tank.

 

[AndyMcD]

Here's my latest brainstormed theory, based upon what I've read, but also some of the points ceg4048 has made have struck a chord with me:

spores have the ability to sense the environment and the changes in the environment. The information they sense include thermal properties of the medium, light, as well as a variety of chemicals and the rate of change of the concentration levels of the chemical. Some chemical changes have the effect of being stimulants which encourage the spores to bloom.

Polluted systems typically have a high positive rate of change of a variety of chemicals such as Ammonia. Other chemicals such as Oxygen may have a negative rate of change.

I think algae spores are waiting for an increasing rate of change in ammonia (not necessarily a high concentration, a spike may be sufficient). When they sense this, they germinate and begin a rapid growth phase.

Ammonia is important to algae for a number of reasons:
- with a higher proportion of protein than plants, a source of nitrogen in a useable form is very important for growth
- it indicates that something in the environment is decaying, possibly meaning less competition from plants
- it means that there is an increasing population of heterotrophic bacteria breaking down proteins to amino acids and hence ammonia. With a large decaying food source the population of bacteria may flourish. The heterotrophic may be out competing the autotrophic bacteria as less ammonia is being converted to nitrates.

Unhealthy plants mean decay, releasing an increased amount of ammonia into the environment.

Effects such as photorespiration (too much light for too little CO2) means the plant may be absorbing less ammonia, acting to increase the ammonia concentration.

However, I also think the algae is then waiting for a reduction in the oxygen concentration, which indicates:
- it is time to stop growing and to produce spores to create the next generation
- photosynthesising plants are producing less oxygen. There is less plant mass and the bacteria's food source may be reducing. The amount of ammonia being released is going to reduce
- the heterotrophic bacteria population is reaching a peak and is consuming much of the available oxygen. The bacteria may be producing the vitamins the auxotrophic algae needs to reproduce

Healthy plants absorb ammonia, are not a source of ammonia and produce oxygen.

 

[sWozzAres]

Presence of ammonia/ammonium and anoxic conditions (lack of oxygen) is known to reduce spore germination, not increase it.

Pollutants, such as heavy metals (Hg, Cu, Cr, Co, Zn, Pb, etc.), pesticides or insecticides (carbofuran, 2,4-D, dithane, phorate, bavistin, parathion, etc.), sewage effluent, crude oil, acetylene, ethylene, ammonium, etc. at various levels decreased spore liberation, motility, settlement, and GRM in different algae (Table X; p. 291).

Biotic factors (including algal and bacterial extracellular products, animal grazing and extracellular products), water stress (except for the need of prior drying for some algal spores), antibiotics (except penicillin at some low level), UV light, and pollution (including heavy metals, pesticides, insecticides, sewage effluents, crude oil, acetylene, ethylene, ammonia or anoxic conditions) at various levels decreased or totally suppressed SG.

Factors affecting spore germination in algae — review
http://link.springer.com/article/10.1007/s12223-009-0047-0

 

[BigTom]

^ Pretty thorough paper that. I've got a pdf if anyone wants it (pm with an email address).

Interesting excerpt (SG = spore germination) -

The SG was decreased not only by the lack of nitrogen, phosphorus or magnesium but also when their (and of calcium) concentration exceed certain levels; e.g., nitrate or phosphate at ≥5-fold level, or magnesium at 10-fold level of that present in the basal medium inhibited akinete GRM in Westiellopsis prolifica (Agrawal and Sharma 1994a). Magnesium at ≥5-fold level or calcium at ≥2-fold level also inhibited akinete GRM in Stigeoclonium pascheri (Agrawal and Sarma 1982a). This indicates that SG in algae is sensitive to high levels of inorganic nutrients. Omission of microelements (ZnSO4, MnCl2, MoO3, CuSO4, Co(NO3)2, H3BO3) from the basal medium increased SG in Stigeoclonium pascheri, and by increasing their concentration to ≥2-fold levels, the condition was reversed (Agrawal and Sarma 1982a). The presence of microelements in the basal medium therefore serves as a check in reaching maximum level of SG under control conditions. More study is needed to clear the role of micro- and macronutrients in SG.