Do plants require more lighting as they grow?

[murphys33]

Hi guys, just wondering if you could help answer my question above... you see, i used a 72 watt light and my foreground plants elatines bubbles from day 1 - however as they grow and almost compeletely cover the foreground, they stopped bubbling - growth rate is still good and at some point, the elatines overlap on top of each other by as much as 1 inch. The bubbling however has stopped. The other day, I put on an additional 55 watt and they started bubbling like crazy again. The blyxa Japonica that i recently put in also started to bubble.


There is not any overhead canopy and all plants received direct 72 watt (original setup) and the additional 55 watt. the addition of the 55 watt caused bubbling again from both existing plants and new plants. I am wondering if there is a need for an increase in lighting as plants grow? How then can onoe explain the fact that the elatines first bubbles but stopped but subsequently bubbled upon addition of another 55 watt? I hae a 25 gallon tank. So 72 watt worked out to be 2.88wpg, while the addition of the 55 watt works out ot be 5.08 wpg. All other factors, fert regime, co2 remains constant

[geoffrey]

No, they don't need more light as they grow.

[oqs]

Hi there. 2 things that I think might have affect the bubbling.

1. The 72W bulb had been used for quite some time and had lost it's initial intensity. This mean it is not supplying the same amount of light as before. Therefore the plants stopped bubbling at this moment. After you added the 55W, the intensity was stepped up to the original amount or even more than it, and the plants start bubbling again. If you want to try if this is the case, you can take out the 55W, and put in a new 72W bulb, and see if the plants bubble.

2. The elatine had overgrown, as you said overlapping each other, and thus shading whatever is beneath causing poor growth. Again you can try thinning out the elatine and see if it bubbles.

oqs

[vinz]

How old are those bulbs?

Another one is water clarity. New tanks usually have very clear water. However, the water will usually turn slightly yellowish and will absorb a fair bit of light as all kinds of things start to leach or dissolve in the water... like tannin from wood, dissolved organics, etc.

Come to think of it, that may explain the plants bubbling after a water change phenomenon!

[dx]

Just a thought: maybe another factor is that the CO2 (and other fertilizer) demand of the WHOLE TANK increases.
I believe the plant need sufficient amount of CO2 for pearling (normally call bubbling). As plant grows, each plant still needs the same amount of CO2 for pearling, but due to the increase in number of plants, every single plant now gets less CO2 at the same CO2 feeding rate. Therefore less pearling. Sounds logical ?

oqs: did you get my PM regarding the LFS in JW ?

[juggler]

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On 9/24/2003 9:52:33 AM

Come to think of it, that may explain the plants bubbling after a water change phenomenon!
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The new water you put in may also replace some nutrients such as Mg and Ca. Which may also explain why I get increased bubbling for even a small change of water.

[geoffrey]

My take is plants have adapted or they have grown heathier. I am just as interested to know but I have yet to come across literatures on this phenomenon.

I also noticed that while most plants in my tank have stop bubbling (they are pearling though and there is a different IMO); just introduced plants often bubble for a while before stopping too. No light intensity was changed prior.

All I can say is you don't need extra light as they grow. Even under shade, plants respond differently and you can tell. They are usually smaller if shaded and their growth rate much slower even with good CO2 and nutrients. Some just remain dormant, like my C. balansae.

As for leaves within the same plants that are shaded, it triggers abscisic hormone. This will cause their petiole to eventually break off from the main plants, eg L. cardinalis and L. grandulosa. In some instances, they will lose all their leafy tissues leaving behind only a vascular skeleton-like structure, eg Echinodorus species.

[oqs]

dw: Got the PM and replied. You didn't get it? Anyway, just want to say thanks for the info, will visit the LFS one of these days.