rayi said:
Right, I think this is the same effect that causes Cryptocoryne rot, for example?
Well, we're talking in general here. I'm not sure that I fully understand the mechanism of Crypt rot. What is bizarre about crypt rot is that it's not usually accompanied by algae on the melting leaves
I would be on thin ice if I offered the theory that it is the crypt that decides to jettison the leaf based on what it perceives to be unfavorable environmental conditions and that it pulls the chemicals away from the leaf in a similar fashion as autumn leaves. On the other hand, a crypt that is unhealthy due to poor carbon or nutrients has algae growing from the leaf without the leaf melting so the rotting/melting seems to me to be a different story.
Ah ha! So if we have a high light tank with CO2 is this the same effect that means you get algae everywhere? Is the benefit of CO2 that the plants get going nice and quick and tidy away the ammonia is short order? Or is there anther factor I am missing?
A high light tank is an unforgiving environment. If CO2 or nutrients are inadequate the breakdown occurs and the algae are triggered. Since the light is high, algae production is accelerated in the same way as plant growth is accelerated by high light. The difference is that algae don't require the quantities of nutrients the plants do but if nutrients
are available this will add to the acceleration. Algae are opportunists. Ejection of ammonia and nutrients at the leaf site explains why algae typically attacks the suffering leaf first.
In air, plants can get all the CO2 they want very easily. They consume tons of this gas in order to strip the Carbon to produce, well... carbohydrates, for growth, seeds, fruit, nectar etc. This is the "prime directive", so carbon is a critical nutrient. In water, gases don't dissolve nearly as easily and so therefore carbon is not easily available. Injecting CO2 allows greater contact of leaf with the gas which now enables photosynthesis and facilitates production/growth. If there is sufficient CO2 for the amount of light the plants next priority is to collect the other nutrients, the most important of which is Nitrogen. The more Carbon is made available the more Nitrogen must be collected. It's easy to see that Nitrate (NO3) and ammonia/ammonium (NH3/NH4) are convenient sources of Nitrogen. If the plants have sufficient CO2 for the level of lighting, then removal of ammonia is assured. This is how healthy plants keep algae in check, by removing this trigger. Algae recognize this by the low level of ammonia in the water column and concede - for the moment. Each species of algae has it's combination of triggers so lets say Phosphates are too low for the plant to collect at the proper rate: Structural breakdown starts to occur in the plant, ammonia and other chemicals leach into the water column near the leaf and you have now generated a set of triggers. Possibly, low PO4 plus ammonia leaching plus high light could be a trigger combination for GSA. It's more complicated than that but that's just a general idea.
I think the Siesta is putting a slight brake on my plant growth, although I'm not noticing any new algae, will let it run for another fortnight and see - like you say - maybe they don't appreciate the interruption. What about midday bursts, anything to support them?
Well it wouldn't surprise me at all if turns out that the siesta actually results in arrested development. No light=no photosynthesis=no carbohydrate production. If someone did a test of 100 of tanks, 50 of which showed significant improvement with the siesta, and if they provided statistically relevant proof I'd have to reconsider my opinion but it just doesn't seem to fit the science model as I understand it.
On the other hand, the noonday burst adds light so as long as there is sufficient CO2 and nutrients at the time of the burst, well, yahoo! more light, more growth. But what happens if you were marginal on the CO2
before the burst? Adding more light with this condition can drag you into the Carbon deficiency zone, right? So there is no free lunch here either. Carbon and light are joined at the hips. There is no way around it. Light+Carbon=Photosynthesis
Cheers,