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Veggie & 24/7 light cycles

GREENIE_420

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This is my first grow and I'm using T5HO's for vegging on a 24/7 schedule and I plan on using HPS for flowering. I know the importance of not disturbing the day/night cycles in the flower stage. With the use of fluros for vegging the plants need to be close to the light source. I was wondering if it has any affect if the plants are removed from underneath the light source for 5 minutes or so in order to water them or inspect them up close. They are not completely removed from the light, I have been simply raising the light fixture enough so that I have room to get at them. These are just "practice plants" until I have everything in place so no big deal. I've read plenty on the lighting subject and I have not come across anything about this.
 

Bong Puller

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I would run 20 on 4 off in veg. just My opinion. But you can take them outa veg for hours with no adverse affcts. As stated (I think??) When you switch over to 12/12 you just need to make sure dark cycle is absolutly dark, no red switches on power strips ect. Pitch black!
B.P.
 

Hick

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mj is in a plant class that does 'not' need a dark period for any metabolic function other than to produce the flowering hormone. 24/0 will produce more growth and shorter internodal distance.
 

Bong Puller

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C&P'D
20/4 has shown me the best in mass, plants very much do need the dark to process. Here's an explanation a bit easier to understand.
Enlightening info on the dark cycle!
C&P'd
Heres an excerpt from mojo's "Basic Coco Grow Plan" I have found it personally to be very accurate and is what I use.

"Here's the post on lighting that got me started on the 20/4 schedule.

I got the information a long time ago and was ignorant enough that it seemed as good a place to start as any. As I said, I've gotten really, really good results using 20/4 so I don't have any reason to think I need to change. If you're not completely sold on what schedule to use or even if you just think you'd like to try it, do so. I didn't do the work in the study and I can't remember who wrote this. Seems to me it was some rogue grower who used to be a part of some group or something that was interested in maximizing growth and yield.

Once again, I don't know the credibility of the author, but the results have been there for me.

Here's the report. The mum lines referred to were "mom" lines according to what gaiusmarius told me once. I thought they were talking about mums as in the flower called a mum. As I remember it, gaius laughed at us for wondering. Must be a British thing, hehe.

In the words of the author:

Lighting Schedule

We did a lot of experiments with light times a few years back using known sativa and sativa dominant clone lines.

With Vegging under HID lights.

20/4 produced the sturdiest growth and the most bulk. Best final yield, taken as 100%
22/2 Less of both growth and bulk. Yield 88%
18/6 Sturdier than 22/2 but slightly less bulk. Yield 87%
24/0 Much lighter in all aspects than 18/6. Yield 79%
16/8 The weediest plants. Yield 67%

Plants vegged to final pots under fluorescents at 20w per sq ft on 18/6 yield 49%

Have not tried 36 hrs dark but did try 48 hrs from 18/6 veg. The final yield was down between 15% and 20% by varying the pure sativas with the biggest loss in final weight and caused the odd herm, [sativas] it did reduce the flowering time by 5 to 8 days.

For the mum lines we have, 20/4 to 12/12 gives the best crop weight and bud quality, really that’s all I’m interested in...


B.P.
 

pcduck

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Bong Puller they frown on live outside links on our forum, and you have a bunch of them. Need to kill them
 

Bong Puller

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I thought I broke em, sorry.
Please search and read the calvin cycle...
B.P.
 

pcduck

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This is what I gathered from a website.

hXXp://plantphys.info/plant_physiology/calvincycle.shtml said:
What is obvious from that is the "connection" to the light reactions. The Calvin cycle needs NADPH and ATP from the light reactions. Thus the Calvin cycle is inseparable from the light reactions...they only occur in the light
Also some more info from the same site.

The 3-phosphoglycerate kinase adds a phosphate from ATP to the 3-PGA to make 1,3-bisphosphoglycerate. Then NADP:glyceraldehyde-3-phosphate dehydrogenase removes hydrogen from NADPH and adds it to the 1,3-bisphosphoglycerate to make glyceraldehyde-3-phosphate (PGAL). In this reduction, a phosphate is removed as well. The resulting NADP+, ADP, and Pi can be recycled to the light reactions. These steps demonstrate why the light reactions and Calvin cycle are interdependent. Without the one, the other comes to a complete halt.
They way I understand it is the more hours of light the more the calvin cycle is working.
 
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Marijuana does not need a dark cycle and should grow all the time the lights are on, if other needs are met. I have also run different vegging light cycles in summer because of heat. I always find that 24/7 gives me tighter internodal spacing and bushier plants than any other method. I have a really hard time believing that something else was not wrong to get 21% less yield when you veg a shorter time. There is also too much left out of that info to really know what was going on. How much light was he using, what was ventilation like, temps, nutes, etc, etc.
 

Bong Puller

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This should make it easier to understand... Not trying to convince(well maybe) you just playing what I have learned foward.
I came across some very enlightening insight to our plants needs for darkness. I'm well aware of the importance of the dark cycle but this gives darkness a whole new light!
WHEN THE LIGHTS GO OUT
By Keith Roberto
and Brandon Mathews

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.
 

Bong Puller

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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!
 

pcduck

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Bog Puller said:
The previous information is primarily regarding a typical tomato plant or flower
Maybe this is just a difference of opinion or just a different type of plant
 

Bong Puller

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What would make cannabis any different? Again guys just sharing my findings, no harsh vibes...
Peace n hair grease,
B.P.
 

pcduck

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Some plants need a dark cycle and some do not.
 

Hick

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Does marijuana require a dark period during the vegetative growth stage? I recently read a grow book that advocated an 18-6 light cycle during the early growth stages.
PSD 420,
Internet

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.
Ed Rosenthal (though I donot find everything he says absolute)

For more information visit

Botany Online:photosynthesis

Photosyntheis lecture from Furnam University

Another C3 and C4 photosynthesis lecture



C3 plants—all of carbon fixation and photosynthesis happens in mesophyll cells just on the surface of the leaf. C3 plants include most temperate plants (except many grasses)—more than 95% of all earth’s plants.



The equation for the Calvin Cycle:

CO2 (Carbon dioxide in from stomata) + RuBP (Ribulose bisphosphate already in plant) + the enzyme RUBISCO (Ribulose bisphosphate carboxylase) “fixes” carbon from the atmosphere à 2PGA (phospholygerate)



PGA enters Calvin cycle in Mesophyll cells à more RuBP (to fix more CO2) + sugar (CH2O)



C3 are inefficient at CO2 fixation because RUBISCO has a greater affinity for oxygen than CO2
Mesophyll cells are packed with RUBISCO
Stomata open during day (CO2, oxygen, and water can all flow out)



Photorespiration undoes CO2 assimilation

2PGA à CO2 + RuBP

increases when there is lots of O2, low levels of CO2, and increased temperature



C4 plants—carbon fixation and photosynthesis split between the mesophyll cells and bundle sheath cells.



The equation:

In mesophyll (carbon fixation):

CO2 + PEP (phosphoenol pyruvate) + PEP carboxylase fixes carbon à OAA (oxaloacetic acid)



OAA diffuses to bundle sheath cells



In bundle sheath (Calvin Cycle):

OAA à malic acid and aspartic acid is decarboxylated à CO2 + pyruvate



Then the Calvin Cycle CO2 + RuBP + the enzyme RUBISCO à 2PGA à RuBP + CH2O



Pyruvate with ATP is moved back to mesophyll and turned into PEP (to fix more CO2)



Feature of many grasses (i.e. big blue stem back campus), corn, and many arid/semi arid shrubs
Calvin cycle in bundle sheath cells where there is no oxygen to be bound by RUBISCO
Very high concentration of CO2 in bundle sheath cells
PEP carboxylase has a high affinity for CO2 so plants must open their stomata less to get CO2 and hence lose less water (especially important in arid regions)
Low levels of photorespiration and higher net photosynthesis than C3 because of low photorespiration
Costly adaptation because it requires lots of ATP (energy)—however, benefits outweigh energy costs.
Stomata are open during the day
Fixation and the calvin cyle are physically separate
hxxp://legacy.earlham.edu/~vandeel/notes.htm

C3 plant

(1) A plant that utilizes the C3 carbon fixation pathway as the sole mechanism to convert CO2 into an organic compound (i.e. 3-phosphogylycerate).
(2) A plant in which the CO2 is first fixed into a compound containing three carbon atoms before entering the Calvin cycle of photosynthesis.


Supplement
C3 plants involve direct carbon fixation of CO2. That is, the initial steps involve the CO2 being bound to ribulose bisphosphate to produce two molecules of three-carbon compound (i.e. 3-phosphogylycerate). The key enzyme that catalyzes carbon fixation is rubisco.

C3 plants must however be in areas where CO2 concentration is high, temperature and light intensity are moderate, and ground water is abundant. This is because in hot areas, the stomata are closed to prevent water loss. However, it results in the rise of O2 level. When this occurs, rubisco reacts with O2 instead of CO2, and leads to photorespiration, which in turn, causes wasteful loss of CO2 in C3 plants.

C4 plant
(1) A plant that utilizes the C4 carbon fixation pathway in which the CO2 is first bound to a phosphoenolpyruvate in mesophyll cell resulting in the formation of four-carbon compound (oxaloacetate) that is shuttled to the bundle sheath cell where it will be decarboxylated to liberate the CO2 to be utilized in the C3 pathway.
(2) A plant in which the CO2 is first fixed into a compound containing four carbon atoms before entering the Calvin cycle of photosynthesis.

Supplement
A C4 plant is better adapted than a C3 plant in an environment with high daytime temperatures, intense sunlight, drought, or nitrogen or CO2 limitation. Most C4 plants have a special leaf anatomy (called Kranz anatomy) in which the vascular bundles are surrounded by bundle sheath cells. Upon fixation of CO2into a 4-carbon compound in the mesophyll cells, this compound is transported to the bundle sheath cells in which it is decarboxylated and the CO2is re-fixed via the C3 pathway. The enzyme involved in this process is PEP carboxylase. In this mechanism, the tendency of rubisco (the first enzyme in the Calvin cycle) to photorespire, or waste energy by using oxygen to break down carbon compounds to CO2, is minimized.
biology online...

A lot of that is pure greek to me, but it explains the difference between c3 plants (mj) and c4 plants.
 

PuffinNugs

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The basic strategy of year round production is to understand the plant has two growth cycles. At germination the plant enters into a vegative state and will be able to use all the continuous light you can give it. This means there is no dark cycle required. The plant will photosynthesis constantly and grow faster than it would outdoors with long evenings. Photosynthesis stops during the dark periods and the plant uses sugars produced to bulid during the evening. This is not a requirement and the plant will grow faster at this stage with continuous photosynthesis (constant light)

--from random grow guide

theres also people that say your having problems in flowre cuase your not giving them a dark cycle in veg..... I say what problems in flowering? my plants flower fine when they are actually mature enough to be flowered, and will have more and tighter nodes, meaning more buds
 
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Bong Puller said:
What would make cannabis any different? Again guys just sharing my findings, no harsh vibes...
Peace n hair grease,
B.P.
What we are saying is that not all plants are the same. Plants have different classifications--some need a dark period and some don't. Cannabis is in the class of plants that does not require a dark period. If you want to give your vegging plants a dark period, then do. However, it is not necessary and I have found that light other than 24/7 causes my plants to stretch and have longer internodal spacing--they simply stretch during the period the lights are out.
 

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