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This appears to be the scientific arguement against a 24/0 light/dark cycle for veg

L

LJB

COORDINATING PHOTOSYNTHETIC ACTIVITY: CIRCADIAN RHYTHMS

source: Louis J. Gross
Professor of Ecology and Evolutionary Biology and Mathematics
Director, National Institute for Mathematical and Biological Synthesis
Director, The Institute for Environmental Modeling
Department of Ecology and Evolutionary Biology
Mathematics Department
University of Tennessee

Under normal conditions, photosynthesis and stomatal opening have circadian rhythms. Here, photosynthesis is measured as carbon assimilation and stomatal opening is measured as conductance to water vapor. For the red kidney bean plant, data shows carbon assimilation varies between 5.8 and 8.2 mmol CO2 per m2 per second, with an amplitude is approximately 2.4 (A = 2.4). The period is approximately 24 hours (p = 24). We can approximate the normal circadian rhythm of photosynthesis as

circadeq2.gif

We can graph the circadian rhythm of photosynthesis over time. The graph of stomatal conductance, the lower curve, is also given, with coordinates on the second axis.

circadfig4.gif


Interpretation: Under a normal 24 hour day-night cycle, both carbon assimilation and stomatal conductance have circadian rhythms. Both tend to be highest at noon, when light energy is highly available, and lowest at midnight.

If changes in light are driving the circadian rhythms, we might expect the sine waves to flatten when a plant is moved to constant light. However, when red kidney bean plants are moved from normal light (day and night every 24 hours) to constant moderate light, the circadian rhythm persists for several days with the same amplitude and period as the above curves. This indicates that changes in light and dark are not driving the circadian rhythm. Instead the rhythm is driven by an internal clock.

The opening and closing of stomata control the concentration of carbon dioxide inside the leaf. When stomatal conductance is high, a larger amount of CO2 can enter the leaf and be available for photosynthesis. Consequently, we might hypothesize that the circadian rhythm in stomatal conductance is causing the rhythm in carbon assimilation. If we manipulate a leaf to have constant levels of CO2, we might expect the rhythms of stomatal conductance and carbon assimilation to disappear. However, under constant moderate light (200 mmol per m2 per second photon flux density) and constant intercellular CO2 (28 Pa), the circadian rhythms still persist for several days with the same amplitude and period as under normal conditions (the curves in the previous graph).

Since photosynthesis is dependent on light energy, we might expect to see changes in circadian rhythm depending on the intensity of light. Under conditions of high light and high CO2, photosynthetic activity is very high. We can determine how such environmental conditions affect the circadian rhythm.

The graph below shows data from a single kidney bean leaflet for the circadian rhythms in carbon assimilation and stomatal conductance under constant high light (500 mmol per m2 per second photon flux density) and constant ambient CO2 (35 Pa).

circadfig5.gif


Under conditions of constant high light, the circadian rhythms in carbon assimilation and stomatal conductance quickly flatten out after a couple of days. The period is slightly longer than 24 hours. Notice that on the first day, the values of carbon assimilation (sy = 17 mmol CO2 per m2 per second) and stomatal conductance (sy = 0.52 mol H2O per m2 per second) were much higher than the values under moderate light conditions (sy = 7 and sy = 0.15, respectively). Under high light conditions, these values decrease over time, along with a decreasing amplitude. This is quite different from constant levels of moderate light, where the circadian rhythms persist for several days with the same amplitude and period as a 24 hour night-day cycle.

Under high light conditions, photosynthetic activity is very high. Therefore it is not suprising the initial values of carbon assimilation and stomatal conductance were much higher than leaflets in moderate light. Under conditions favorable to high photosynthetic activity, carbohydrate quickly accumulates in the leaves. The resulting decline in carbon assimilation and stomatal conductance over time may have occurred as starch accumulated in the leaves, disrupting chloroplast structure.

Conclusions: The cellular clock of plant cells is well adapted to the 24 hour day-night cycle of the planet. Circadian rhythms arise in various aspects of photosynthesis, including carbon assimilation, stomatal conductance, and in levels of essential elements of photosynthesis, such as Photosystem II and RuBP. Changes in light intensity and carbon dioxide concentration can affect circadian rhythms of photosynthesis.

Circadian rhythms are essentially sine waves with periods of 24 hours and variable amplitudes. Quantifying properties of circadian rhythms, such as amplitude and period, can help us understand the mechanisms controlling rhythms.

500 mmol per m2 per second photon flux density (PPFD) is most certainly exceeded by anyone that uses 400+ watt MH and HPS lamps...As for lower wattage HID, T5 and CFL, I cannot say for sure.
 
L

LJB

I think there were quite a few of us that agreed with the common sense argument that there is no 24/0 light/dark cycle in nature, therefore there shouldn't be one used for the indoor garden. After all, the purpose of the greenhouse or enclosed grow room is to duplicate nature!

That isn't to say I don't eliminate the possibility of a better light/dark cycle than 12/12 for cannabis sativa in particular, but all plants clearly need a break from the sun and/or intense artificial light.

Photosynthesis peaks at noon. Some plants have two or three or four more smaller peaks later in the afternoon. And it's been demonstrated that environmental conditions matter. For example, a plant species grown in a cooler and more humid environment could have fewer peaks and a more or less constant, steady rate of photosynthesis than the same plant grow in an more dry and hot environment, but with equal levels of light.
 

ibjamming

Active member
Veteran
Are there any "experiments" here? Someone MUST have done it already...grown a batch (clones) in 16/18/24 hours of light and compared them... Anyone have a link to it? I can't believe it hasn't been done...
 
L

LJB

Are there any "experiments" here? Someone MUST have done it already...grown a batch (clones) in 16/18/24 hours of light and compared them... Anyone have a link to it? I can't believe it hasn't been done...

I've only seen second hand references to such tests and haven't conducted one myself yet.
 

superpedro

Member
Veteran
This is considered a fact, and the example is used in a textbook of general Plant physiology.
The 24/0 plants also use much longer time to adjust to 12/12.
IMO the use of long periods of darkness is useless too. It only offsets the rhythm.
You can cut days of your stretch period if you go from 18/6 to 12/12, by adding 3 hours of darkness at the start and end of your darkness period, there by keeping the middle of the "night" at the same time.
If you just ad 6 hours at the end or start, the plant will take time to adjust it's new rhythm.
 

Owl Mirror

Active member
Veteran
I think there were quite a few of us that agreed with the common sense argument that there is no 24/0 light/dark cycle in nature, therefore there shouldn't be one used for the indoor garden.

Could it also be said that there doesn't exist in Nature, conditions equal to hydroponics ?
I'm always amazed at folks growing plants in a bucket of nutrient-rich water, rather than SOIL.
While it may be possible to grow plants this way, I feel something is lost through this unnatural process.

Any thoughts ?
 
L

LJB

Here we go, SuperPedro, the floodgates open.

Plant Circadian Rhythms

C. Robertson McClung
Department of Biological Sciences Dartmouth College

***

When The Lights Go Out
by Keith Roberto and Brandon Matthews 2006-03-01
Maximum Yield magazine

All plants have complex energy generating systems that function both in sunlight and in the dark. However, these reactions are coupled and rely on the products and intermediates produced by each biochemical process, day or night. In short, plants use light energy, water and CO2 during photosynthesis to generate sugar and oxygen that is later metabolized by the dark reactions to generate cellular CO2 and energy. Carbon dioxide generated in the dark cycle is used as the carbon source for maintenance molecules and some is even expelled by the plant. There are many common misconceptions regarding the role of CO2 in the dark, but it will soon become clear what plants do without their beloved sunlight.

cont.
 
L

LJB

Could it also be said that there doesn't exist in Nature, conditions equal to hydroponics ?
I'm always amazed at folks growing plants in a bucket of nutrient-rich water, rather than SOIL.
While it may be possible to grow plants this way, I feel something is lost through this unnatural process.

Any thoughts ?

That begs the question, "what is soil"?

growing medium. A vital component of container culture, providing nutrients, water, air, and the rooting environment essential for the development of a healthy...

We don't grow plants without light or water or minerals, but we do grow them without soil.

Did that blow your mind, or what? haha just kidding.
 

Owl Mirror

Active member
Veteran
That begs the question, "what is soil"?

We don't grow plants without light or water or minerals, but we do grow them without soil.

Did that blow your mind, or what? haha just kidding.

It's true, same as an average human can live on Big Mac and fries but, it isn't what the body needs to be healthy.

19492.jpg


soil-versus-hydro-grown1.JPG
 

unclefishstick

Fancy Janitor
ICMag Donor
Veteran
I think there were quite a few of us that agreed with the common sense argument that there is no 24/0 light/dark cycle in nature, therefore there shouldn't be one used for the indoor garden. After all, the purpose of the greenhouse or enclosed grow room is to duplicate nature!

That isn't to say I don't eliminate the possibility of a better light/dark cycle than 12/12 for cannabis sativa in particular, but all plants clearly need a break from the sun and/or intense artificial light.

Photosynthesis peaks at noon. Some plants have two or three or four more smaller peaks later in the afternoon. And it's been demonstrated that environmental conditions matter. For example, a plant species grown in a cooler and more humid environment could have fewer peaks and a more or less constant, steady rate of photosynthesis than the same plant grow in an more dry and hot environment, but with equal levels of light.


there are two areas of 24 hr light on our planet,above 60 north latitude and 60 south during the respective summer periods,i know everything grows like crazy in alaska during the summer,only takes a month after the last frost before the grasses are head high.
 

Kcar

There are FOUR lights!
Veteran
I wonder if that hold true for seeds that pop under 24/0?
There are plenty of weeds in the arctic that only see 20/4 - 24/0 their whole life cycle.
Are those plants all messed up? I was up there in 95 and can attest to the vigor
of plants growing in natural 24/0.
 

Kcar

There are FOUR lights!
Veteran
Jinx! Sorry UncleFishSticks, now you can't post until I say "Jinx" again. Oh damn.
 

Kaneh

Member
There are plenty of weeds in the arctic that only see 20/4 - 24/0 their whole life cycle.
Are those plants all messed up? I was up there in 95 and can attest to the vigor
of plants growing in natural 24/0.

Midnight sun is something that everyone should see atleast once in life! You have to go above arctic circle thou.
In middle of night sun is WAAYYY above horizon. Very psychedelic!
I usually try to spend summer solstice up there.:xmasnut:

The reason plants grow very fast here is the very short summer.
At spring time after snow has melted, nature just explodes with shades of green! :party:
 

Owl Mirror

Active member
Veteran
Midnight sun is something that everyone should see atleast once in life! You have to go above arctic circle thou.
In middle of night sun is WAAYYY above horizon. Very psychedelic!
I usually try to spend summer solstice up there.:xmasnut:

The reason plants grow very fast here is the very short summer.
At spring time after snow has melted, nature just explodes with shades of green! :party:

While that may be true, how much landrace Marijuana grows above the Arctic Circle ?
There might be a reason the majority of Marijuana grows between both 35 lat degrees.
I'm unsure of the results, trying to force some fine Jamaican to grow under lighting and seasonal conditions not found in the vicinity of Jamaica.

I think more people would be successful growing if they knew the pedigree of the strain and researched the proverbial roots (it's origin).
Isn't that what determines if it's a 6, 8, 10, 12, etc... week flowering strain?
The distance from the equator where the strain originated.
 
I don't get why people keep needing some scientist to them how to grow... do some simple tests and you'll find out for yourself, that's what I did and now I know which works better.

It's easy to do, take some clones from the same mother plant and put half in 24 light, and the others in 18 hour of light. I did this a few times and the ones that had a dark cycle always rooted faster and healthy.
Then I did the same test with rooted clones in soil. The clones in 18/6 roots grew faster and stronger. The plants were a bit slower, but only until the roots developed well.

So that closes the book on the subject for me, it's all I need to know and care about. Any science background about why and why not, I really don't give a crap about.
I just want to point that out, cause some many people just keep beating this dead horse. And they will just end up testing it and finding out on their own anyway.
 

geopolitical

Vladimir Demikhov Fanboy
Veteran
You're forgetting that there are three major flavors (and lots of mixes) of carbon fixation in photosynthesis, C3, CAM, and C4. Not all photosynthetic routes require darkness, not all of them require the same energy, water or heat levels.

Cannabis, last time I checked, was primarily C4.
 

*mr.mike*

Member
No, this is not a scientific argument in the least. It is simply the results of observation on "some plant" under certain constant conditions.

I read the link, and took a few things that would shut down anyone trying to use this as a basis of an "argument."

"...in 1729, a French scientist discovered that circadian movements were not dependent on the daily cycling of light and dark."

Ooops... a BIG shut down.

"Conclusions: ...Changes in light intensity and carbon dioxide concentration can affect circadian rhythms of photosynthesis."

Oh, so the circadian rhythms can change according to light schedule and CO2? So these rhythms are "plastic" and plants seem to adapt, quite easily, such as Japanese hydroponic lettuce farms which out yield nature.

Also, notice the remark where carbon assimilation could be dependent on starch concentrations.

It's hard to say that this is anything to suggest that a "natural" cycle is superior to a 24 hour light cycle, especially when we can see much better yields in plants such as autoflowers, many which have been under 24 hours of light for more than 25 generations.
 

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