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I was wondering what determines internodal distance in stem plants? Is it a genetic thing or is it environmentally determined? If it is environmentally determined, what are the factors? It is, of course, nicer to have bushy growth, which would require short internodes, than leggy ones.
 

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I think lighting has something to do with it...I remember reading somewhere about having brighter light to shorten the distance between nodes. There may be other factors involved also.
 

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Bert H,

Few of us in different regions of US determined that having higher K levels of light will have noticeable impact on internodal distance.

Steve Hampton (FL), Tula (CA), Vicki (KY), Ghazanfar (VA) and myself (NJ); we all did test run about 4 years ago by using 9325K vs. 6700K and difference was well noticeable. Ambulia was one of the samples.

9325K level helped plants to form shorter internodes and created "bushy" growth.

Some people disagree with that :idea:
 

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Bert,

To add onto what Jay said. I've experienced similar things with my tanks.

Taking wavelength and energy into consideration with the way light is diffused in water it makes sense that light higher in the blue spectrum would encourage plants to grow "leggier". As one goes deeper into water more spectra are removed by the water until only blue is left because it's higher in energy. Plants grown in high blue light would tend to react to that by trying to grow as tall as possible as quickly as possible, resulting in longer internodal lengths.

You can also get the same results by growing plants in nutrient poor water under high light. I've got some of that going on in one of my tanks right now.

Best,
Phil
 

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What happens when you use a mix of both? I have no expierence with PC, because all I have been using is VHO..
 

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Another way to shorten internodes is through nutrition. High PO4 (2 ppm), lower NO3 (5-10 ppm) will help shorten internodes in several plant species.

I believe higher PO4 levels are a cure all for a wide variety of problems we seem to see in our tanks --spot algae, internodal distances, and bringing out red coloration. I could never get my Ludwigia arcuata blood red like in Amano's books until I raised the PO4 levels a tad.

Carlos
 

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I used to use gro-lux tubes with their purple-blue color, and it always seemed to me that the plants were more compact with that lighting than with cool-white, even if i have higher wattages of cool-white.

A high ratio of red light (wave length, 660) to far red light (wave length 730) encourages compact growth.
 

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Here's a small study done on terrestial plants and compact growth. I have yet to try this myself, but have startet looking for bulbs in the fare red specter. Might be my english messing stuff up for my, but from what I could gather, it's enough to bombarb the plants in far-red for 15 minutts and the end of day???

http://www.clemson.edu/hort/sctop/bsec/bsec-08.htm

http://194.236.255.117/akvarienet/memberfiles/th_of_plantsfile54.pdf

.3 Stem elongation
As described in section 2.2, far-red light reflected by neighbouring plants (or neighbours for short) decreases R:FR in horizontally propagated light, as 'seen' by vertically oriented plant surfaces (see Aphalo and Ballaré, 1995). This happens at low canopy densities, so it is especially important for small seedlings in sparse canopies.
The stems of many plants elongate faster if they receive additional far-red light from the side (see Ballaré, 1999, and references therein). In general, the magnitude of the response to far-red
light depends on the species, developmental stage, and other environmental variables such as blue light and/or photosynthetically active irradiance incident on the leaves. However, at low canopy densities there is no actual shading of leaves by neighbours. When measured under laboratory conditions, the stem elongation response to far-red light incident on the stem can be shown to have a very short lag (of the order of minutes in small seedlings) but continue for some time after the end of the stimulus (Casal and Smith, 1988a,b).
The photoperception of the lateral far-red light takes place in the growing internodes. In sparse canopies, the perception of neighbours is mediated mainly by phyB and probably sensitivity is modulated by phyA6.
 

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Prolonged light periods and overworked plants will result in high internodal distances.... from experience.
 

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I had the same results Jay and others noticed with different lights. We have to be careful however when we generalize by saying "Kelvin", I have a hunch spectrum has more to do with it than overall kelvin rating.

The GE 9325, which has a strong peak in red, seemed to me as the better light out of the ones I tried.

I think Phil has a great point, plants are not deep water species and there must be a mechanism for them to know when they are at the right depth. We all know that if lighting is insufficient the plants grow leggy and grow quickly towards the surface. I'm sure this occurs in nature as well when a plant is situated too deep, in this case the spectrum of the light it receives would be robbed of much of it's red. So perhaps the balance of red and blue in the spectrum is what tells a plant that it's at the right depth. If so, then a lot of red, such as these 9325K bulbs, could cause the opposite effect and trigger the plant to grow even denser than normal. Just a guess though...

Amount of light does play some role in it, mostly when the light is insufficient though. I have noticed better quality of growth in ludwigia repens in my 1wpg low light tank using the GE 9325K bulbs than my 4wpg using 10000K and 67000K bulbs.

I haven't noticed nutrient levels play a significant role in internodal length however, mostly color and health from what I could tell.

Giancarlo Podio
 

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gpodio, that's just about the highlight of the stuff I posted earlyer on. This test concluded that the light that was filtered true the canopy of the tree's would incurrage the plant to grow in high to chase for the top where most of the ligh was. If you would bombard a plant in fare-red light, it would focus on it's sidegrowth.

This bulbs you talk about sounds perfect, guess I should see if they are available here in Norway to. Anybody have a full name of spec on them?
 

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Wait! Wait!, you guys!! The studies showed that decreasing the far-red (730) light gave more compact growth. Some of you seem to be looking for bulbs that have higher amounts of far red. If you want compact growth, you want as much red light (660) and as little far red light (730) as possible. When plants are shaded by taller plants, the red light is absorbed or reflected much more than far red. The increased ratio of far red to red causes the internode elongation. Far red reflected off of other plants coming in horizontally seems to be especially effective in causing internodes to elongate.

If we want compact plants, we want as little far red as possible.
 
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