for a scientist and bearing in mind your arguments through out this post, this statement "Surely some plants outcompete some algae, and some algae outcompete some plants." seems somewhat out of character!
where is the proof? the evidence for your claims?
All I meant here is that there are tens of thousands of plants, and hundreds of thousands of algae, and there's going to be variation in growth rate, mechanisms for absorbing nutrients, sensitivity to pH, and so on. I have no idea *which* algae outcompete plants, and *which* plants outcompete algae (however we define this vague concept) but I'm sure some do. My background is in zoology, and the idea of competition is important, and animals that compete well in one set of circumstances don't in another. To take an obvious example, polar bears and grizzly bears are extremely closely related and live in adjacent parts of the world, and while their ranges overlap in some parts, mostly they're separate because each outcompetes the other in specific sets of conditions.
and how is this meaningless? its fundamentally linked to EVERY planted tank in existence, surely?
I don't actually see how "competition" for nutrients makes much of a difference. There are tanks with high levels of nitrate where algae are rampant, and seemingly similar tanks with high levels of nitrate where they don't. The assumption that plant growth is somehow the factor has been often put forward, but I'm not aware of any experimental evidence to back it up. At best, it's an hypothesis: fast-growing plants outcompete algae for nutrients and/or CO2, suppressing their growth. I have no idea if it's actually true.
examples to support your hypothesis would be nice. it seems most unscientific to make claims without backing them up!
What, that certain plants do well under high intensity lighting? Surely that's obvious. If you recall your A-level biology, you'll remember you learned about shade-tolerant plants (which typically had large, dark green leaves) and bright light plants (which typically had smaller, bright green leaves). Each type of plant is optimised for certain levels of light intensity, and does best when provided that level of light intensity. Shade-tolerant plants can't grow so fast because they have to invest more energy in chlorophyll and the hardware for catching light. Bright light plants grow faster because they accumulate energy more quickly. You can test the relationship between light intensity and photosynthesis experimentally. A classic GCSE biology practical you may have done involved moving a lamp closer to, or further away from, some
Elodea in a glass jar. You can count the bubbles rising from a cut stem, and the more light, the more bubbles. The more bubbles, the faster oxygen is produced, and therefore the faster photosynthesis takes place. If you have a bright-light plant, like
Elodea, you'll find that it has a very high rate of photosynthesis maximises at a high light intensity. A shade-tolerant plant, like
Anubias, say, would reach a lower maximal rate of photosynthesis, and would do so at a lower light intensity. The differences comes down to how bright-light tolerant plants have systems that allow to avoid limiting factors (such as CO2) at higher light intensities than shade-tolerant plants. In other words, they've invested in enzymes that work well with less CO2 than shade-tolerant plants, which needn't bother, since CO2 isn't likely to be a issue for them. I'm simplifying wildly here, and botany isn't my specialist subject by any means, so I'd encourage you to review photosynthesis, C4 pathways, and so on at your leisure.
Yes, you can tweak things like CO2 to get plants to grow better under less light than they would grow without CO2. But that's not the same thing as saying a couple of incandescent bulbs will get your
Samolus valerandi looking lovely! For photosynthesis to take place *at all* a threshold light intensity is required. Less light than that, and nothing will happen, however much CO2 you provide. That threshold varies for plant to plant, and there's something called the compensation point where the rate of photosynthesis exceeds the rate at which the plant uses up energy for basic metabolic processes. So to grow, you need not just the threshold value, but the compensation point value as well.
It's a well known scientific fact blue light penetrates water better than red light. Tubes with more red light than blue will tend to be less useful in deep tanks than tubes with a strong blue output. In other words, if you have a reddish 25 watt tube and a bluish 25 watt tube, more of the energy from the bluish one will get to the bottom of any given aquarium. It should also go without saying that plants with specific leaf colours, such as red rather than green, will be optimised for collecting light of particular wavelengths (in the case of red leaves, just the blue). So again, if you want your red plants to stay red, or simply to grow, they will do best given lights that provide lots of blue.
Cheers, Neale
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