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Do Vegging Plants Need Any Dark Time?


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#1
Drakeroberts

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Hi guys,

With so many people doing the 24/0 vegging cycle I was wondering why vegging plants dont need the Dark (Calvin?) cycle? I thought that the leaves collected C02 all day and then created glucose/sucrose at night during the dark cycle. Is that just plants creating fruit? (Budding) I mean its undisputable ..you can veg 24/0. But Why? Plants didnt evolve to be in 24/0 sunlight. something inside them must know its un-natural.

#2
community

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I think there is a dark period in nature for a reason, however, if you want minimal dark...go with a 20/4, but I think a 18/6 is the best.
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#3
Smokeitdown

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You can go 42/0 without any problems. Cannabis does NOT need a dark period to grow. Unlike other plants, its photosynthesis is done completely in the light hours, while some plants do part of the process in the dark hours. Therefore, you really do not need a dark time until flowering. Doing a 24/0 schedule will also reduce vertical growth making your plant more bushy.
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#4
law_101

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why during 12/12 do they get a jump in growth? I have noticed growth over a 12 hour dark period in flowering.. I know that 12/12 triggers flowering but to me it seems like it helps growth too.

#5
Drakeroberts

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You can go 42/0 without any problems. Cannabis does NOT need a dark period to grow. Unlike other plants, its photosynthesis is done completely in the light hours, while some plants do part of the process in the dark hours. Therefore, you really do not need a dark time until flowering. Doing a 24/0 schedule will also reduce vertical growth making your plant more bushy.


I know you meant 24/0 not 42/0 Lol --> Thanks for the info. That raises a question in my mind. Lets see if I can blow anyones mind with this next possible theory.

Ok so Cannabis does it thing in the light...great. That means the darkness only serves to notify the plant what season it is. This is good. This means that if we can find a way to artificially trigger budding cycle ..i.e. supplementing a specific hormone, or some other unknown mechanism---->then we could grow buds under 24/0 light and double production rate. 2 - 12hour cyles in one day. Any one else see what im getting at? All that time in the dark is only doing one thing . . .telling the plant to create buds. If we can do that in place of the dark period of 12 hours then thats time saved right?

As I understand it: Budding is triggered by the build-up of a specific hormone that is only created in the dark. Once this hormone reaches a critical level it alters the plant from veg to bud. The plant willcontinue to bud so long as this critical level is reached each night. SO--> if we artificially introduce that specific triggering hormone then---> the plant should be thinking "Lets bud out" regardless of light a schedual at 24/0.

Thoughts?

#6
amoril

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#7
rudar

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try finding someway to artificially degrade the Pr molecule.


how about dressing it in a uncle same costume in front of a tax office? :smoking:

#8
Drakeroberts

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the problem is, scientists still havent actually been able to isolate this 'hormone'

in fact, the concept that its a hormone is actually just theory. Granted, a well established one, but not one thats well supported.

what actually does happen, is phytochrome degrades. when phytochrome is in a stable form, the plant grows vegetatively. when the Pr degrades to PBr, the plant initiates flowering.

even when fully established in flowering, the first few hours of the dark period still contain more Pr than PBr.

so, if you really want, try finding someway to artificially degrade the Pr molecule.



Thanks man you got me lookin around and I found this------>
MARIJUANA OPTICS

An elaboration on the phytochemical process that makes THC


by Joe Knuc

The resin exuded by the glandular trichome forms a sphere (1) that encases the head cells. (2)

When the resin spheres are separated from the dried plant material by electrostatic (3) attraction and placed on a microscope slide illuminated with a 100W incandescent bulb, they appear very dark when observed through a 300X microscope. Since orange, red, and infrared are the component wavelengths of incandescent light, and since the absorption of light makes an object dark or opaque to the frequency of the incoming wave, one can conclude that these wavelengths are probably not directly involved in energizing the cannabinoid pathway. (4)

However, the resin sphere is transparent to ultraviolet radiation. (5)

The author found through trial and error that only one glandular
trichome (6) exhibits the phytochemical process that will produce the amount of THC associated with pain relief, appetite stimulation and anti-nausea; euphoria and hallucinations are side-effects, however. This trichome is triggered into growth by either of the two ways that the floral bract is turned into fruit. (7)

Of all the ways that optics are involved in the phytochemical production of THC, the most interesting has to be how the head cells and cannabinoid molecules are tremendously magnified (8) by the resin sphere. These and other facts are curiously absent from the literature. The footnotes update the literature to include electrostatic separation of the resin sphere from the dried plant material and marijuana parthenocarpy.


(1) "For all spheres, a ray drawn perpendicular to the sphere's surface will intersect the center of the sphere, no matter what spot on the surface is picked, and the magnifying power(a) of a glass sphere is greater the smaller its size. A sphere of glass can also bring light that is heading to a focus behind it to a point within it, with freedom from two aberrations, spherial aberration and coma, but not from chromatic aberration. Chromatic aberration results when different wavelengths are focused on different planes and is the most difficult of the aberrations to correct. The human eye lens also exhibits chromatic aberration, but a yellow pigment(B) called the macula lutea in the fovea, an area at the rear of the eyeball, corrects this problem by the way it absorbs blue light."

(a)"The formula to calculate the magnifying power of a sphere is l=333/d, where l is the magnifying power and d is the diameter of the sphere expressed in mm."

(b)Interestingly, the resin exuded by drug-type flowering female marijuana plants has a yellow tint. Could this pigment work to correct chromatic aberration in the resin sphere like the macula lutea does in the fovea for the eyeball?

RETURN

(2) Quoting from the Mahlberg and Kim study of hemp: "THC accumulated in abundance in the secretory cavity where it was associated with the following: cell walls, surface feature of secretory vesicles, fibrillar material released from disc cell wall, and cuticle. It was not associated with the content of the secretory vesicles."

The resin spheres contain the THC. It is not contained in the leaf or floral bract. After the resin spheres are dissolved in solvent or dislodged by electrostatic attraction, and a microscopic examination of the leaf or floral bract has revealed that only the glandular trichomes' stalks remain, no effect will be felt after smoking the dried plant material from which the resin spheres have been removed.

RETURN

(3) The electrostatic collection of the resin spheres from dried marijuana plants with plenty of ripe seeds has been for hundreds of years the method indigenous people of North Africa and Lebanon have used to make hashish. Obtain a round metal can 8" or so in diameter x 3" or so in depth (the kind that cookies come in) with a smooth lid. Obtain 2 ounces of dried marijuana with plenty of ripe seeds in the tops. To remove the seeds and stems, sift the marijuana tops through a 10-hole-to-the-inch wire kitchen strainer into the can. Close the can with the lid and vigorously shake the closed can three or four times. This gives the resin spheres an excess negative charge. Let the can sit for a moment and then remove the lid. Opposites attract. The negative-charged resin spheres have been attracted to the metal surface of the can and lid which has a positive charge. Take a matchbook cover or credit card and draw the edge across the surface of the lid. Note the collected powder. Observed under 300X magnification, the collected powder from this "shake" is composed of resin spheres with an occasional non-glandular trichome. As the marijuana is shaken again and again, and more of the yellow resin spheres are removed from the plant material, the collected powder gradually becomes green-colored as the number of non-glandular trichomes increases in the collected powder. The greener the powder, the less the effect.

RETURN

(4) "Cannabinoids represent a dimer consisting of a terpene and a phenol component. Cannabigerol (CBG) is the first component of the pathway. It undergoes chemical change to form either cannabichromene (CBC), or cannabidiol (CBD). Delta 9-tetrahydrocannabinol (THC) is derived from CBD."

RETURN

(5) "Pate (1983) indicated that in areas of high ultraviolet radiation exposure, the UVB (280-320 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD. The extent to which this production is also influenced by environmental UVB has also been experimentally determined by Lydon et al. (1987)."

The writer's own experience allow for a more specific conclusion: If the UVB photon is missing from the light stream(a), or the intensity as expressed in W/cm2 falls below a certain level(B), the phytochemical process will not be completely energized with only UVA photons which are more penetrating but less energetic, and the harvested resin spheres will have mostly precursor compounds and not fully realized THC©.

(a)Examples of an environment where the UVB photon would be missing from the light stream include all indoor cultivation illuminated by HID bulbs and in glass or corrugated fiberglass covered greenhouses.

(b)"The maximum UVB irradiance near the equator (solar elevation angle less than 25 deg.) under clear, sunny skies is about 250 W/cm2. It was observed that the daily solar UVB in Riyadh, Saudi Arabia (N24.4Lat.) decreased from September to December by about 40% (Hannan et al. 1984). The further a person is from the tropics, the less UVB radiation there is: the average annual exposure of a person living in Hawaii is approximately four times that of someone living in northern Europe." Below are some UVB readings taken in Hoyleton, Illinois, on a clear sunny day in June by David Krughoff as reported in Reptile Lighting 2000.

7am: 12 microwatts/cm2
8am: 74 microwatts/cm2
9am: 142 microwatts/cm2
10am: 192 microwatts/cm2
11am: 233 microwatts/cm2
12pm: 256 microwatts/cm2
1pm: 269 microwatts/cm2
2pm: 262 microwatts/cm2
3pm: 239 microwatts/cm2
4pm: 187 microwatts/cm2
5pm: 131 microwatts/cm2
6pm: 61 microwatts/cm2

©Cannabinoid pathway: Anywhere in this pathway UVB
(320 nm - 290 nm) does a better job than UVA (400 nm - 320 nm) in energizing a phytochemical reaction that will produce more fully realized THC because "all cannabinolic compounds show an absorption maximum between 270 and 280 nm in the ultraviolet region."

RETURN

(6) Capitate-stalked glandular trichome.

RETURN

(7) #1: The ovum has been fertilized and there is a seed developing: In the areas of the Northern Hemisphere where indigenous people have grown heterozygous drug-type marijuana for hundreds of years, pollination is used to trigger the growth of the capitate-stalked glandular trichome on the floral bract and concomitant leaves of the flowering females before the autumnal equinox(a) so the majority of seeds will be ripe(B) before November.

(7) #2: The floral bract has become parthenocarpic. Parthenocarpic fruits develop without fertilization and have no seeds. Except for transmutation and turning lead into gold, there has been more nonsense written about seedless marijuana than on any other subject. In marijuana parthenocarpy, the floral bract (the fruit) enlarges in size as though there were a seed growing inside, and the capitate-stalked glandular trichome is triggered into growth on the floral bract and concomitant leaves. "Most popular supermarket tomatoes are parthenocarpic which was induced artificially by the application of dilute hormone sprays (such as auxins) to the flowers." In a trial, marijuana parthenocarpy was not induced by the application of the spray used on tomatoes. Only the photoperiod© will trigger parthenocarpy in flowering female marijuana plants. Marijuana parthenocarpy occurring before the autumnal equinox is considered by the author to be "long-day" and marijuana parthenocarpy occurring after the autumnal equinox to be "short-day".

The longest photoperiod that will trigger parthenocarpy in unfertilized flowering homozygous(d) Indica female marijuana plants is 13:00 hours, give or take 15 minutes. This effect can be obtained in the month of August at N35Lat, and because the capitate-stalked glandular trichomes received plenty of UVB during this month at this latitude, the harvested resin spheres had fully realized THC. Rating: euphoria and hallucinations, major appetite boost and pain relief, deep dreamless sleep. These plants seldom grow taller than four feet but potency makes up for the reduced harvest.

The gene pool is heterozygous if a flowering female marijuana plant is not parthenocarpic by the end of the first week in September in the Northern Hemisphere. If this is the case, pollination is used instead of parthenocarpy to trigger the growth of the capitate-stalked glandular trichome before the autumnal equinox to obtain as much fully realized THC as possible in the harvested resin spheres by the time the majority of the seeds are ripe.

The longest photoperiod that will trigger parthenocarpy in unfertilized flowering heterozygous female marijuana plants is 11:00 hours, give or take 15 minutes: This effect can be obtained in the month of November at N35Lat. Because of the low intensity of UVB radiation at this latitude at sea level during November, the harvested resin spheres evidenced only slightly more THC than precursor compounds. Rating: mild to medium euphoria, appetite boost and pain relief, good snooze.

Thai marijuana falls into this 11:00 hour category, and its parthenocarpy is characterized by an inflorescence in which many floral bracts are attached to an elongated meristem. It is these elongated meristems that are harvested to become a THAI STICK. On the other side of the world, Mexican marijuana grown around the same latitudes (Michoacan, Guerrero, Oaxaca) also falls into this short-day parthenocarpic category and the unfertilized marijuana will become "sensimilla" in the 11:00 hour photoperiod which begins in mid-December in that region. The winter sunshine in those latitudes has more UVB intensity than the winter sunshine at N35Lat.

All unfertilized flowering female marijuana plants will become parthenocarpic in a 9:00 hour photoperiod (15:00 hour dark period): This can be obtained in the month of December at N35Lat. At this latitude in this month there is not even enough UVB in sunlight for precursor vitamin D3 to develop in human skin. The phytochemical process will not produce THC whenever the UVB and UVA photons in the light stream fall below a certain level of intensity expressed in W/cm2. Rating: no effect.

(a)In the Northern Hemisphere above the Tropic of Cancer, the key to all marijuana potency is this: The more days of sunlight the capitate-stalked glandular trichomes' resin spheres accumulate before the autumnal equinox the more fully realized THC.

(b)It is recognized in the indigenous world that drug-type marijuana with a majority of ripe seeds will produce more euphoria, hallucinations, appetite stimulation, pain relief, and sleep aid than with a majority of unripe seeds.

©The photoperiodic response is controlled by phytochrome. "Phytochrome is a blue pigment in the leaves and seeds of plants and is found in 2 forms. One form is a blue form(Pfr), which absorbs red light, and the other is a blue-green form(Pr) that absorbs far-red light. Solar energy has 10X more red (660nm) than far-red (730nm) light causing the accumulation of Pfr." The first and last hour of a day's sunlight is mostly red light because of the scattering effect on blue light. "So at the onset of the dark period much of the phytochrome is in the Pfr form. However, Pfr is unstable and returns to phytochrome Pr in the dark." The red light in sunrise returns the Pr to the Pfr form. "Phytochrome Pfr is the active form and controls flowering and germination. It inhibits flowering of short-day plants (the long night period is required for the conversion of Pfr to Pr) and promotes flowering of long day plants."

(d)In Nepal and nearby areas of India where the capitate-stalked glandular trichome is triggered into growth by parthenocarpy rather than by fertilized ovum, great care is taken to make sure that all male marijuana plants are destroyed as soon as they reveal their sex. This is because unfertilized Indica flowering females can have both stigma and anther protruding from the floral bract. In the Indica gene pool, female-produced pollen carries an allele for long-day parthenocarpy, and seeds resulting from this female-produced pollen will produce another generation of female plants that will also exhibit long-day parthenocarpy during flowering. But if pollen from male plants is introduced into this gene pool, the resulting seeds will produce a generation of females that will exhibit short-day parthenocarpy instead. The allele for long-day parthenocarpy in the female-produced pollen is carried into the gene pool by self-pollination and cross-pollination, and perhaps homozygous is used too loosely here to describe the genetic result.

RETURN

(8) It appears that the resin sphere acts as an UVB receptor and magnifying lens. The latter apparently lets it gather in a lot more photons than would otherwise be possible; because a lens also acts as a prism, the resin sphere may prevent some wavelengths from being focused where the phytochemical processes are taking place because they could interfere with the efficiency of the phytochemical process that makes THC.


#9
smoove

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Thanks man you got me lookin around and I found this------>
MARIJUANA OPTICS...

If this type of more in depth scientific (and pseudo-scientific) discussion interests you... BROWSE THROUGH THIS THREAD There are many references to this article and others like it, along with some debate which may loosely relate to this topic. (but mostly uvb specifically.)

-----

With regard to your last post... Horticulturists have been researching how plants know when to flower and bloom for quite some time now. There seem to have been some recent advances in understanding the process but it is still a giant mystery. The process is not nearly as simple as you decribed it, and scientists have actually located specific sets of genes and proteins which play an even larger role in this process. The bottom line is however, that scientist are hard at work trying to figure this out and as soon as any applicable and affordable methods of applying these discoveries are available to horticulturists... we cannabis growers will definitely be taking advantage of it. :smoke:
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#10
Drakeroberts

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If this type of more in depth scientific (and pseudo-scientific) discussion interests you... BROWSE THROUGH THIS THREAD There are many references to this article and others like it, along with some debate which may loosely relate to this topic. (but mostly uvb specifically.)

-----

With regard to your last post... Horticulturists have been researching how plants know when to flower and bloom for quite some time now. There seem to have been some recent advances in understanding the process but it is still a giant mystery. The process is not nearly as simple as you decribed it, and scientists have actually located specific sets of genes and proteins which play an even larger role in this process. The bottom line is however, that scientist are hard at work trying to figure this out and as soon as any applicable and affordable methods of applying these discoveries are available to horticulturists... we cannabis growers will definitely be taking advantage of it. :smoke:



Ahh I see....so Ive learned just enough to start asking the same questions as everyone else. . . . or at least I made it to the same wall of understanding as the rest. Thanks guys. I guess I will leave the work up to the Botonist and such from here on out.

Drake

#11
FaderVader

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You want fast growth 24/0

You want stronger root growth 18/6 veg

"And you can quote me!"
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#12
Ender87i

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Heres the way i see it... When the lights are on, the plant is using "most" of its energy to COLLECT light, and "the rest" of its energy to GROW... When the lights are off, the plant is using ALL of its energy to GROW, using the light that it collected during the day... So although the plant is ABLE to grow with the lights on, the fact of the matter is that its main focus is to collect light, and is only focusing a small amount of energy into growing, while when the lights are off its only focus is to grow..

#13
smoove

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Heres the way i see it... When the lights are on, the plant is using "most" of its energy to COLLECT light, and "the rest" of its energy to GROW... When the lights are off, the plant is using ALL of its energy to GROW, using the light that it collected during the day... So although the plant is ABLE to grow with the lights on, the fact of the matter is that its main focus is to collect light, and is only focusing a small amount of energy into growing, while when the lights are off its only focus is to grow..

That's some awesome stoner logic :hello: unfortunately you're incorrect. I don't have the time to break down your statement, just don't want anyone to take this information and run with it. Plant physiology is not limited to "growing" and "collecting light" There are so many processes that require the use of energy wether created through photosynthesis, respiration, or taken from reserves. There is plenty of evidence showing that cannabis will grow perfectly well under 24 hours of light, and plenty of that evidence even suggests that it may grow faster without any dark period.

In the future you may want to avoid using phrases like "the fact of the matter is" ...when the fact of the matter is... that you're not using any facts to begin with. ;)

#14
Ender87i

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In the future you may want to avoid using phrases like "the fact of the matter is" ...when the fact of the matter is... that you're not using any facts to begin with. ;)



Smoove - HOWEVER, the fact of the matter IS that during a (for example) 18/6 light schedule, your plants will IN FACT grow MORE during the dark state than during the light state... Not only have i tested this, but it is also a widely known fact that you could find to be true almost anywhere on the internet (or bookstore) that you look.. MJ in fact does do MOST (or MORE, at least) of its growing in the dark... And because of this, it also makes it true that its focusing less on growth during the light period, and for what other reason would this be than that the plant is putting most (or alot) of its focus on collecting light and turning it into energy... Im not saying the plant doesnt grow during the light stage, but it does (as a matter of fact ;)) grow less than it does in the dark.
Am i right, or am i right? :P

Edited by Ender87i, 01 May 2009 - 09:20 PM.


#15
smoove

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Smoove - HOWEVER, the fact of the matter IS that during a (for example) 18/6 light schedule, your plants will IN FACT grow MORE during the dark state than during the light state... Not only have i tested this, but it is also a widely known fact that you could find to be true almost anywhere on the internet (or bookstore) that you look.. MJ in fact does do MOST (or MORE, at least) of its growing in the dark... And because of this, it also makes it true that its focusing less on growth during the light period, and for what other reason would this be than that the plant is putting most (or alot) of its focus on collecting light and turning it into energy... Im not saying the plant doesnt grow during the light stage, but it does (as a matter of fact ;)) grow less than it does in the dark.
Am i right, or am i right? :P

Negative ghost rider... just more stoner logic. Maybe you're confusing growth with stretch?

It is NOT a widely known fact that cannabis does most of it's growing in the dark. Let's be more specific though so we can narrow down this debate. What you're saying is that during the Vegetative period of a cannabis plant under an 18/6 light cycle, that the plant will grow more during the 6 hours of darkness than during any 6 hour period of lights on? Also that a cannabis plant will end up with more growth under an 18/6 light cycle than a 24/0 light cycle?

Is this correct?

Edited by smoove, 01 May 2009 - 10:07 PM.

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#16
Ender87i

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Sounds pretty close to what im saying.
I do believe that an 18/6 cycle will grow better than a 24/0 cycle, not only because of experience, but why do you think its the most widely used vegetative cycle? Because weather the fact that it closely mimmicks the natural cannabis outdoor habitat matters or not, it grows more in the dark. Maybe its because it has the most energy stored after its light period, and has nothing else to focus on but to grow? or maybe thats just stoner logic.. But aside from that particular detail, my statement is in fact true. Its only logical ;) Lets hear YOUR explaination chief.

#17
uphill

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Amazing how little we know about our favorite plants. Many people are too cautious to share and others just pass along what they heard not what they experienced.

One more thought on photoperiod. If you start flowring with 36 to 42 hours of dark and flower 12-12 for 10 days, you can change cycle to 11.5 on and 6 off to increase yield with no ill effect. This effect is improved by adding the same ingredients used in tissue culture agar, ommitting the rooting hormone and the gel (hardener). Adding this to res. (I rec. hand watering to prevent ex. contamination) for 4-5 days during the 3rd week of flowering will increase harvest. This will also delay finish as the plant tries to force an additional set of buds.

#18
smoove

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Ender87i: First let me preface my response with my opinion on the light cycle debate. I've grown under both 18/6 and 24/0 light cycles and when considering growth alone, I honestly don't have a preference with either. I've had great success with both but I only veg my plants for 2 weeks, any longer and they'd end up overgrowing my space. Now, throw electricity and heat into the mix and I begin leaning toward including a dark period. So just to be clear, I'm not arguing which one is "better." I'm arguing that your breakdown of plant physiology is misguided and some of the information you're throwing out here as "fact" is in fact, just your opinion. Even experience is subjective... just because something works for me does not mean it works for everyone the same, you get what I'm saying? With that said... here's some of MY explanation ;)

Ender87i:

When the lights are off, the plant is using ALL of its energy to GROW

No, there are so many other things a plant uses it's energy for other than "growing" when the lights are off. Here's a short article to back up my statement. It basically says C3 plants (cannabis included) are incredibly busy with a multitude of processes during the dark cycle.

When The Lights Go Out
by Keith Roberto and Brandon Matthews

Everyone knows that plants need light for photosynthesis. What they don’t know is that plants need darkness, too! But why? Are they trying to get a restful sleep for a busy day of photosynthesis? Not many people try to grow plants in continuous light. It seems we all have a hunch that the dark cycle is an important part of a plant’s life, but what are they really doing? This article will shed some light on the mysterious and often misunderstood dark cycle.

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.

We must keep in mind that plants are pre-historic and have developed complex metabolic systems to adapt to an ever changing environment. Plants used to enjoy an atmosphere of highly concentrated carbon dioxide before they did us a favor and converted it to oxygen. As the globe varies greatly in temperature, humidity, and light conditions, plants have diversified to cope with their geographic neighborhood. Forced to adapt to modern times, plants now have specialized systems to utilize the relatively low concentration of atmospheric CO2, around 0.036% or 360ppm. To best provide for any plant species, an artificial environment should closely resemble their natural conditions. Once these conditions are understood, further steps can be taken to enhance plants’ metabolic activity.

When the sun goes down, a greenhouse environment undergoes a few fundamental changes such as a shift in light wavelength and a decrease in temperature. As the sun sets, the wavelength of light generated by the sun shifts from blue to red. During the day, photosynthesis is most efficiently propelled by blue light (450nm) because it is a shorter wavelength and thus carries more photon energy. At sunset, red light (650nm) initiates a sequence of chemical responses that trigger essential metabolic processes to begin. Similar to humans, plants spend the day gathering energy (money) and generating (buying) food. In the evening they metabolize this food to provide their cells with the energy they need to form new cells, repair damaged cells, produce important enzymes and proteins, and prepare themselves for sunrise and photosynthesis. Essentially, they carry out cyclic processes known as a circadian rhythm, from Latin meaning “approximately a day.”

All cellular events require metabolic energy, primarily in the form of ATP or NADH. These high energy molecules are manufactured by many biochemical processes, as plants have evolved to scavenge energy at all periods of the day. Photosynthesis is the process by which a plant uses light energy to break apart water, generating O2, protons and electrons. Oxygen is the magical energy transporter in all forms of aerobic respiration, and is used to transfer electrons in the production of the energy rich molecules ATP and NADH. Coupled to the products of photosynthesis, the Calvin Cycle fixates CO2 to generate 3-Carbon sugars during the light cycle. These sugars are later converted into 6-Carbon sugars like glucose and fructose, the primary substrates used to make cellular carbon and the bulk of ATP and NADH during aerobic respiration of the dark cycle.

As fragile as plants appear to be, they are dedicated survivors and thrive in a wide range of light and temperature conditions. Temperature is as important a variable as light because it directly affects humidity, dissolved gas concentrations, water stress, and influences the ratio of water loss to carbon fixation. Changes in the leaf are most prevalent because they are the primary site of light absorption, sugar formation, and gas exchange. During the night, stomates in the leaf are nearly closed as the need for gas exchange is small and to prevent unnecessary water loss. During the day when photosynthesis is in full swing, the demand for CO2 uptake is great and stomata are wide open. Unfortunately, high temperatures increase water loss through the same stomatal openings that are trying to uptake CO2. Therefore, photosynthesis is both temperature and light dependent as an increase in temperature reduces the amount of carbon that is fixed, or carboxylated, into sugar by the Calvin Cycle. Photosynthesis reaches a maximum rate at a temperature of 30°C (85ºF) and remains efficient ± 5°C (75-95ºF).

The leaf is a very complex organ. Stomates are surface pores on the underside of the leaf that are regulated by guard cells that vary the size of the pore in response to environmental cues. Water and CO2 cannot be simultaneously transported through the narrow stomata. Fortunately, during the day when water is readily available, many stomata are dedicated to CO2 uptake rather than water transpiration. This factor is known as the Transpiration Ratio. In a typical C-3 plant, approximately 500 molecules of water are lost for each single molecule of CO2 fixated by a leaf. The most abundant protein in the leaf, around 40%, is the one responsible for CO2 fixation, known as ribulose bisphosphate carboxylase/ oxygenase, commonly called rubisco and abbreviated RuBP. As the chemical name suggests, this protein is capable of accepting both CO2 and O2. This is a competitive reaction, but fortunately, RuBP has a much higher affinity for carbon dioxide than oxygen. Throughout a typical day, carboxylation occurs three times more than oxygenation of RuBP.

There are a few barriers to CO2 uptake in a leaf. The first is boundary layer resistance where a thin, unstirred layer of air on the under surface of the leaf reduces CO2 diffusion. This resistance decreases with leaf size and wind speed. The second is intercellular air space resistance which hinders the diffusion of CO2 between layers in the leaf. The third, and major contributing factor, is stomatal resistance, which is a direct regulation by the stomata to gas exchange.

Temperature has a direct affect on the transpiration ratio. Not only does heat induce water loss through stomata, an increase in temperature also reduces the concentration of dissolved CO2 in air, thus favoring oxygenation of RuBP rather than carboxylation. This negative effect is known as photorespiration, the use of oxygen instead of carbon dioxide. Be careful not to confuse this term with aerobic respiration which is the process of glycolysis, the breakdown of sugar to generate metabolic energy which will be discussed later. Shade plants have more chlorophyll per unit area and also have very low photorespiratory rates. Sun plants have more rubisco per unit area and can handle a higher photosynthetic load.

It is always a good idea to supplement a greenhouse with CO2 during the light cycle when stomata are open and gas exchange is readily occurring. Simply doubling the ambient concentration to 700ppm will increase the photosynthetic rate by 30-60%. At optimum light and temperature conditions with supplemental CO2, photosynthesis is only limited by the ability of the Calvin Cycle to regenerate the first sugar acceptor molecule, ribulose-1,5-bisphosphate. On the other hand, in low CO2 concentrations more carbon dioxide is given off during aerobic respiration at night than diffuses into the leaf during the day. This ratio is known as the CO2 compensation point.

Why would the rubisco protein have evolved to use both CO2 and O2? Plants are highly adaptable and need to be able to thrive in tropical conditions of great light intensity and high nighttime temperatures that favor water loss and low ambient CO2 concentration. Even a typical environment can have extreme conditions out of the average range. In addition to the Calvin Cycle to fixate carbon dioxide, plants have a backup mechanism that recovers lost potential when oxygen associates within the active site of RuBP. The Photorespiratory Carbon Oxidation cycle (PCO) is a minor process that converts oxygenated RuBP into a small amount of cellular CO2 by rearrangement of the amino acids glycine and serine.

In fact, there are a few mechanisms by which plants concentrate intracellular CO2. The previous information is primarily regarding a typical tomato plant or flower, the C-3 class of plants in which photosynthesis produces a 3-Carbon sugar. Other classes of carbon fixation include C-4 and CAM processes of desert and grasslike plants that live in the hottest and driest conditions. The stomata of these plants are closed during the day and open at night to make the most efficient use of water. Because there is little to no photosynthesis occurring in the dark, the uptake of CO2 is low, and these C-4 and CAM mechanisms concentrate carbon dioxide to be used by the Calvin Cycle.

During the dark cycle, plants undergo aerobic respiration. Respiration is divided into three parts: Glycolysis, the Kreb or Citric Acid cycle (TCA), and the Electron Transport Chain. Glycolysis is the breakdown of sugars to shuttle smaller sugar molecules and intermediates to the Kreb Cycle. The Kreb Cycle then generates cellular CO2 and energy rich molecules like ATP, NADH and FADH. These energy carriers are then incorporated into the electron transport chain, coupled to the protons and electrons produced during photosynthesis to establish a proton gradient across the chloroplast thylakoid membrane, similar to a battery. The Kreb Cycle generates on average 34 molecules of ATP per 6-Carbon sugar. This represents a net ATP gain as many more molecules are produced than consumed in all other metabolic processes.

Red light plays an important role in the regulation of the dark cycle. Red light is the color of the rising and setting sun. Plants temporally govern most biochemical processes by a circadian rhythm, a type of internal biological clock. In a natural environment this rhythm is set to a 24 hour cycle, although a plant can be trained to operate on however many hours a light and dark cycle add up to. Interestingly enough, it is rhythmic because even in constant darkness the biological functions persist in a cyclic fashion, although if left in complete darkness over time the rhythm does fade away. Such processes include leaf movement, flowering and ripening response, and the regulation of enzymes and hormones. The main protein responsible for this response is known as phytochrome.

Phytochrome, abbreviated Pr , is converted to its active form, Pfr , upon irradiance by red light (650nm). Conversely, it can also be reconverted and deactivated by irradiance of far-red light (720nm). The activity of phytochrome is not solely dependant on its active form, but rather on the ratio of Pfr to the total phytochrome concentration. In this way, plants can sense the movement of the sun and the length of day. In addition to absorbing in the red light region, phytochrome also shows a slight response in the blue-light region (450nm). In combination with other blue light photoreceptors, this response is responsible for solar tracking of leaves as the sun moves through the sky.

The flowering response has been determined to be a result of the length of darkness a plant receives. Inversely, a plant that flowers with short nights are termed Long Day Plants (LDP). A typical vegetable plant that matures in early Fall, when nights become longer, are termed Short Day Plants (SDP). Because plants are adapted to absorbing whatever photons they can, whenever they can, as in a shady forest, interrupting the dark cycle with light can dramatically alter its circadian rhythm. SDP are more sensitive to this response than LDP. Just a five minute irradiance can have an affect, whereas a LDP would need about one hour of light interruption to take affect.

Regulation of a plant’s energy metabolizing systems function on many levels. A biochemical pathway can only proceed as fast as the rate limiting enzyme or substrate. The primary source of regulation is genetic. Chloroplasts and mitochondria have their own genetic code that produce the enzymes needed for their respective process. The only way to up-regulate genetic expression is either through genetic engineering or producing more of these genes by making sure the plant has all its required nutrients to produce more new cells. Another mode of regulation is through the limiting pathway intermediate, as mentioned regarding CO2 supplementation where the limiting factor becomes the regeneration of ribulose-1,5-bisphosphate. Unfortunately, the regeneration of this substrate is also regulated by the electron transport chain. Sometimes a limiting reactant can be artificially added to increase metabolic activity, as in the addition of amino acids, hormones and cofactors like trace vitamins and minerals. Ultimately, the major mode of regulation is environmental. Changes in water properties, nutrient availability, temperature, light duration and strength, humidity, and dissolved gas concentrations are big obstacles that need to be orchestrated to achieve maximal metabolic activity.

As one can see, plants are definitely not getting a restful sleep at night. To keep up with our demand for their products and beauty they need to work around the clock. Plants have concrete biochemical processes and care should be taken to provide the proper environment. One cannot expect a plant to flourish as if by magic. After all, we all have our own personal needs and your plants do too!

Bibliography

Berry, J.A., Downton, J.S. 1982. Environmental regulation of photosynthesis. Photosynthesis, Development, Carbon Metabolism and Plant Productivity. Vol 2: 263-343.Academic Press, New York.

Ehleringer, J.R., Sage, R.F., Flanagan, L.B., Pearcy, R.W. 1991. Climate change and the evolution of C-4 photosynthesis. Trends in Ecological Evolution. Vol 6: 95-99.

Taiz, L., Zeiger, E. 1998. Plant Physiology. 2nd Ed. Sinauer Associates, Sunderland, MA.

Vince-Prue, D. 1986. The duration of light and photoperiodic responses. Photomorphogenesis in Plants. Martinus Nijhoff, Dordrecht, Netherlands.

Wiskich, J.T., Dry, I.B. 1985. The tricarboxylic acid cycle in plant mitochondria: Its operation and regulation. Higher Plant Cell Respiration. Vol 18: 281-313. Springer, Berlin.

Zeiger, E., Farquhar, G., and Cowan, I. 1987. Stomatal Function. Stanford University Press,Stanford, CA.

Maximum Yield - Indoor Gardening



Ender87i:
...the fact of the matter IS that during a (for example) 18/6 light schedule, your plants will IN FACT grow MORE during the dark state than during the light state... Not only have i tested this, but it is also a widely known fact that you could find to be true almost anywhere on the internet (or bookstore) that you look.

This is not a fact Ender. Widely known... anywhere on the internet... bookstore? I don't even have to look far to contradict your statement. Let's just pull an article from somewhere on the internet who is a widely known marijuana horticulturist and author who has written books that you can find... you guessed it, in a bookstore.

Need the dark?
Ask Ed: Ed Rosenthal

One way in which plants are categorized is by the way they gather and handle carbon dioxide. Cannabis is a C3 plant. It uses the CO2 it gathers during the light period, when it is photosynthesizing. Plants designated C4 also gather CO2 during the dark period for use during the light period. Many C3 plants, including cannabis, do not need a rest period. They continue to photosynthesize as long as they are receiving light.

The plant's photosynthetic rate determines its growth rate because the sugars are used by the plant to build tissue and for energy. Cannabis under continuous light will grow 33% faster than the same plants on an 18-6 light regime

Need the dark | Cannabis Culture Magazine



I don't doubt that you've had success with your methods, but it's important to distinguish between facts, opinions and subjective experiences. What you're stating are opinions based on your experience, and the plant physiology you've been throwing out there is based on "beliefs" and your own logic, not based on facts.

I do have more to say... but maybe if I find the motivation at another time, but it's late now and I'm tired. Hope I made some sense here or any of this info is useful to anyone.

Edited by smoove, 02 May 2009 - 08:43 AM.

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StoneyJake

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Smoove - HOWEVER, the fact of the matter IS that during a (for example) 18/6 light schedule, your plants will IN FACT grow MORE during the dark state than during the light state... Not only have i tested this, but it is also a widely known fact that you could find to be true almost anywhere on the internet (or bookstore) that you look.. MJ in fact does do MOST (or MORE, at least) of its growing in the dark... And because of this, it also makes it true that its focusing less on growth during the light period, and for what other reason would this be than that the plant is putting most (or alot) of its focus on collecting light and turning it into energy... Im not saying the plant doesnt grow during the light stage, but it does (as a matter of fact ;)) grow less than it does in the dark.
Am i right, or am i right? :P


Everyone knows that a plant with a dark period will be taller. Who the hell wants taller plants? I like my plants to have short spacing between nodes and avoid stretching as long as possible. Indoor is all about efficiency not height of the plants..


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