tony456 said:
Stringy plants. Here's what I think you're telling me with the links. Old school says - most aquarium plants are amphibious, they're biologically programmed to seek light just like a terrestrial plant, solution - more light. School of the avant guard says - they are biologically programmed to seek CO2, solution - more CO2. Am I on the right lines? Is it not possible that low levels of light and/or CO2 could be responsible for a plant making a straggly bid to get to the atmosphere? Is it not likely to vary from species to species depending on the environment they evolved in? Would an immersed plant with its leaves in the CO2 rich atmosphere not go stringy if deprived of light?
Well it's easy to make an argument for almost any parameter, but biological programming does not occur in the same way as we might imagine. There is a hierarchy of things that plants need and this hierarchy determines the plant response. There are also different mechanisms involved based on the particular need of a plant in a deprived environment. So we need to first understand the plant needs, the environment and then the mechanisms in order to unravel the mysteries.
To get a deeper understanding you have to study the article linked in the 7th post of that first thread I listed by the OP. I'll link to it again here. The article is entitled
Ethylene Sensitivity and Response Sensor Expression in Petioles of Rumex Species at Low O2 and High CO2 Concentrations
The problem in this hobby is that everyone automatically thinks about light first when they think about plants. They don't think that plants do anything but eat light. So that becomes their focus to the exclusion of all else. Very few people think about the fact that plants breathe. That they have a network of channels and that gas exchange in plants is as important as light. Plants deprived of the gasses they need die as quickly as those that are deprived of light. Without Oxygen a plant cannot burn the food it makes to feed it's cells. Without CO2 it cannot even make the food, the glucose that the cells need. Without these two gases therefore, it doesn't matter how much light is available. The plant will suffocate and starve very quickly.
The illusion of the overriding importance of light is made stronger because of the ease with which we ourselves can see light. We know right away the difference between dim and bright, but we can't see CO2 or O2. But try the following experiment:
1. Try closing your eyes for 5 minutes. Any effects? No?
2. Try holding your breath for 5 minutes. Effects? Yeah, I'll bet.
This experiment demonstrates the hierarchy I mentioned above. That we can do without light for quite some time in comparison to the length of time we can do without gas exchange. Even though plants are autotrophs, and even though they need light more than we do, the situation is actually quite similar for them in that they can easily deal with poor lighting but they cannot easily deal with poor gas exchange. Without excellent gas exchange, and without access to gases, light is rendered completely irrelevant.
Therefore, under conditions of poor gas exchange, the plant's response is to seek better gas exchange at all cost. At that point it really does not care about how much light there is because it is suffocating. The mechanism by which this happens is that the plant constantly produces very tiny amounts of a hormone called Ethylene, a HydroCarbon with formula C2H4, and which also happens to be a gas. The only gaseous hormone. The reason evolutionary forces developed a gaseous hormone for aquatic plants is actually ingenious. All gasses encounter a reduction in solubility and diffusion rates at 4 orders of magnitude in water. So the way that a plant is aware that it is in water is that the water will cause the gaseous hormone to diffuses slowly in exactly the same way that CO2 and O2 diffusion slows down. The same mechanism of slow Oxygen and CO2 transport which suffocates the plant also slows the diffusion into the water column of Ethylene, so the Ethylene concentration in the tissues builds up. Ethylene receptors in the tissues are then triggered and this tells the plant to use it's resources to extend the distance between the nodes - to elongate in order to get to the surface where O2 and CO2 are abundant.
When people flood a tank, they have absolutely no clue that what they are doing is suffocating their plants. All they can think about is pumping as many megawatts of light in some misguided concept of how plants grow. They do not realize that CO2 and Oxygen is 10,000 time LESS available in the water than they were in air. They have no idea of the C2H4 tissue buildup. So they never realize that you need to inject high doses of CO2 and that you need to have a high mass flow rate over the tissue surface in order to carry away the C2H4 so that the concentration in the tissues do not build up and is carried away from the plant. That's one of the primary functions of high flow rates in a planted tank.
Terrestrial plants that elongate in deep shade is a completely different set of conditions, and the elongation does occur based on the higher proportion of Far Red wavelength (near 700 nm) that are prevalent in shade. This is a completely different set of environmental conditions and has nothing to do with flooded plants. So in that article the author talks about how an aquatic Rumex species responds according to the gases that are supplied whereas the non-aquatic Rumex species does not respond in the same way. The response of the aquatic Rumex to these conditions is how most all the aquatic plants behave under similar conditions. When your aquatic plants elongate therefore, it means that you should conclude that CO2 and flow is poor and the plant is responding to poor gas exchange. The Matrix does not teach you about this. It tells you to add more light but that is just another illusion.
tony456 said:
EI. Your tutorial says that 20ppm/week is the unlimited threshold dose for NO3. So that would mean in the case of the tap supply being 40ppm (mine is close to that) and a 50% weekly water change there would be no need to dose for nitrates?
The correct procedure is to dose the amounts given in the tutorial and to forget about what you think you have in your water. No one can actually measure the real NO3 levels in water unless they have access to advanced scientific equipment. Neither the municipality you get your water from nor your hobby grade test kit
can accurately give you these values so the best policy is to dose the suggested amounts of KNO3 powder. If at some point you wish to lower the dosages then you can do so easily.
tony456 said:
You give the unlimited light threshold as 5w per gallon. Hang on that's not sounding so cutting edge! Is that your funny old tube thingies? How much light per watt? What shaped tank? What I'm trying to work out is amount of light - PAR or Lumens/Sq meter - that equates to your 5w/g. Sorry if its posted somewhere but I couldn't find it.
I'm sorry but I don't know the answer to that question. No PAR readings were reported for exactly the same reason you gave in your post. Meters are expensive so everyone just muddles on. So few people have any idea about what PAR even is, much less know what the values in their tanks are. Barr might have been using T5 fluorescent over the 20G tank. The whole point of the article is to demonstrate that increased light generates an increased growth rate with a corresponding increase in nutrient demand. He was not trying to determine specific lighting values or to correlate PAR values to nutrient levels. Besides, there is no real way of reproducing exactly the photonic conditions or to calibrate them on a curve. There are some charts however that plot T5 and T8 wattage against PAR and distance from the bulb. I'll have to search for those as they are very useful.
tony456 said:
And, If I wanted to go for a system operating at say 50% of that threshold - given that there would plenty of CO2 and correct EI nutrition levels. How much light do I need?
Again, you'll not find any chart that describes that. First of all, every plant has a different Light Compensation Point and they respond differently. Light causes radiation damage to plants, a phenomenon known as photoinhibition, which actually destroys their tissue structure. The ability of each species to repair the damage and to protect themselves from high light poisoning varies widely. What Barr mentions generally is that if you can measure PAR you can use a low stress setting to generate somewhere around 40 micromoles at the substrate, a medium setting would generate about 75 micromoles at the substrate and a high setting would generate about 100-150 micromoles at the substrate level.
These numbers show how wide a tolerance based on CO2 and nutrition plants can adapt to. So the question of "need" is irrelevant. More light generatse faster growth but it doesn't mean that plants under high PAR are any healthier than plants living under low PAR. That is THE misguided basis that people use to justify high light. Having lots of CO2 means that you can use even lower PAR numbers. So the only real "need" of a plant is to stay above LCP, which, for most plants is somewhere between 10-20 micromoles, which is very very dim. I saw a non-CO2 tank the other day in a dentist office, and it was so dim I couldn't make out the plants at the bottom of the tank. I had to put my nose right up to the glass to peer through the darkness It was a cheesy grolux 15 watt T8 and the tank was a hexagon just under 3 feet deep. I was able to make out loads of some of the most beautiful Anubius I had ever seen. Perfectly healthy with a waxy sheen and zero algae.
Asking this question about how much light you "need" is like asking how fast you need to drive on the road. There is no need.
tony456 said:
Ps. If you have any video or photographic project in mind please message me. If I can help out I'd be happy to.
Well what we really need is some photography tutorials, either equipment selection, post-processing using popular image software, or even tutorials on photographic technique would be useful, so that's the sort of expertise that would be useful for that section. If you think you might like to contribute in that way let any of the staff know. [/quote]
Cheers,