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acespicoli

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While both purple and green phototrophic bacteria and cyanobacteria are types of bacteria that utilize light for photosynthesis, the key difference is that cyanobacteria produce oxygen as a byproduct of photosynthesis, whereas purple and green phototrophic bacteria do not; this is because cyanobacteria use water as an electron donor, while the other groups use alternative sources like hydrogen sulfide, making their photosynthesis "anoxygenic" (not producing oxygen).

Key points to remember:
  • Pigments:
    Both groups use light-absorbing pigments for photosynthesis, but cyanobacteria use chlorophyll similar to plants, while purple and green bacteria use bacteriochlorophyll which absorbs different wavelengths of light.

  • Electron donor:
    Cyanobacteria use water as an electron donor during photosynthesis, resulting in oxygen release. Purple and green bacteria typically use hydrogen sulfide, producing elemental sulfur as a byproduct.

  • Ecological niche:
    Due to their oxygen-producing ability, cyanobacteria can thrive in a wider range of environments compared to purple and green bacteria, which are usually found in anaerobic environments where hydrogen sulfide is present
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  • Pure Haze
    Breeder Choice Organisation150sativaregular
    Purple Kush #1Breeder Choice Organisation-mostly indicaregular
    Royal Purple KushBreeder Choice Organisation63mostly indicaregular
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acespicoli

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Scientific classification Edit this classification
Kingdom:Plantae
Clade:Tracheophytes
Clade:Angiosperms
Clade:Eudicots
Clade:Rosids
Order:Rosales
Family:Cannabaceae
Genus:Cannabis


The plant chloroplast is considered primary because it descends from this original endosymbiotic relationship between host cell and cyanobacterium. It is thought that the ancestors of today's plant chloroplasts may have become endosymbionts over one billion years ago (see here).

 

acespicoli

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Figure 5.​

Figure 5

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Morphological characteristics of the cannabis plants during the vegetative phase and the reproductive phase. (A) Two stipules (small, leaf-like structures found at the base of a petiole), demonstrating the juvenile phase. (B) Bracts (modified leaves found just below a flower) and solitary flowers (i.e., perigonal bracts and style), demonstrating the reproductive phase. stp: stipule; sty: style; br: bract; pbr: perigonal bract.

screenshot-www_ncbi_nlm_nih_gov-2025_01_11-21_50_50.png

There was substantial growth related to plant height associated with the long-day photoperiod (18/6). During the long-day photoperiod, the plant height increased from 4.05 ± 0.62 cm in seedlings with cotyledons to 81.23 ± 3.51 cm in plants with the twelve true leaves (Figure 7). In addition, the longest secondary branches in the lower part of the plant extended to a maximum length of 19.28 ± 1.52 cm (Figure 7).


Once the phyllotaxy shifted from opposite to alternative, the photoperiod was changed to short-day conditions (12/12). To prevent the potential misidentification of solitary flower stigmata within the apical zone as inflorescences, the commencement of inflorescence development was delineated as the point where a minimum of three pairs of stigmata became discernible atop the apical shoot. After 10 days of the short photoperiod, inflorescence was observed atop the apical shoot at node 15. At the full-flowering stage (after 15 days of the short-day photoperiod), the main inflorescences became evident at the apical extremity of both the main stem and secondary- and tertiary-order branches (Figure 7 and Figure 8). Moreover, all leaves of the main and axillary shoots were in an alternate phyllotaxy. The plant height in the short-day photoperiod increased from 81.23 ± 3.51 cm to 113.62 ± 7.58 cm (Figure 7). In addition, the longest secondary branches in the lower part of the plant extended to a maximum length of 25.31 ± 3.24 cm (Figure 7). It is notable that the augmentation of plant height and secondary branch length in the short-day photoperiod exhibited reduced growth compared to the long-day photoperiod (Figure 7).


Plants (Basel)
. 2023 Oct 22;12(20):3646. doi: 10.3390/plants12203646


Rudimentary. Sound advice for growers wishing to avoid herm stress
 

acespicoli

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List of notable plant breeders​




Dwarfing​

Dwarfing is an important agronomic quality for wheat; dwarf plants produce thick stems. The cultivars Borlaug worked with had tall, thin stalks. Taller wheat grasses better compete for sunlight but tend to collapse under the weight of the extra grain—a trait called lodging—from the rapid growth spurts induced by nitrogen fertilizer Borlaug used in the poor soil. To prevent this, he bred wheat to favor shorter, stronger stalks that could better support larger seed heads. In 1953, he acquired a Japanese dwarf variety of wheat called Norin 10 developed by the agronomist Gonjiro Inazuka in Iwate Prefecture, including ones which had been crossed with a high-yielding American cultivar called Brevor 14 by Orville Vogel.[36] Norin 10/Brevor 14 is semi-dwarf (one-half to two-thirds the height of standard varieties) and produces more stalks and thus more heads of grain per plant. Also, larger amounts of assimilate were partitioned into the actual grains, further increasing the yield. Borlaug crossbred the semi-dwarf Norin 10/Brevor 14 cultivar with his disease-resistant cultivars to produce wheat varieties that were adapted to tropical and sub-tropical climates.[37]

Borlaug's new semi-dwarf, disease-resistant varieties, called Pitic 62 and Penjamo 62, changed the potential yield of spring wheat dramatically. By 1963, 95% of Mexico's wheat crops used the semi-dwarf varieties developed by Borlaug. That year, the harvest was six times larger than in 1944, the year Borlaug arrived in Mexico. Mexico had become fully self-sufficient in wheat production, and a net exporter of wheat.[38] Four other high-yield varieties were also released, in 1964: Lerma Rojo 64, Siete Cerros, Sonora 64, and Super X.

Double harvest season​

Initially, Borlaug's work had been concentrated in the central highlands, in the village of Chapingo near Texcoco, where the problems with rust and poor soil were most prevalent. The village never met their aims. He realized that he could speed up breeding by taking advantage of the country's two growing seasons. In the summer he would breed wheat in the central highlands as usual, then immediately take the seeds north to the Valle del Yaqui research station near Ciudad Obregón, Sonora. The difference in altitudes and temperatures would allow more crops to be grown each year.[citation needed]

Borlaug's boss, George Harrar, was against this expansion. Besides the extra costs of doubling the work, Borlaug's plan went against a then-held principle of agronomy that has since been disproved. It was believed that to store energy for germination before being planted, seeds needed a rest period after harvesting. When Harrar vetoed his plan, Borlaug resigned. Elvin Stakman, who was visiting the project, calmed the situation, talking Borlaug into withdrawing his resignation and Harrar into allowing the double wheat season. As of 1945, wheat would then be bred at locations 700 miles (1000 km) apart, 10 degrees apart in latitude, and 8,500 feet (2600 m) apart in altitude. This was called "shuttle breeding".[33]


Locations of Borlaug's research stations in the Yaqui Valley and Chapingo
As an unexpected benefit of the double wheat season, the new breeds did not have problems with photoperiodism. Normally, wheat varieties cannot adapt to new environments, due to the changing periods of sunlight. Borlaug later recalled, "As it worked out, in the north, we were planting when the days were getting shorter, at low elevation and high temperature. Then we'd take the seed from the best plants south and plant it at high elevation, when days were getting longer and there was lots of rain. Soon we had varieties that fit the whole range of conditions. That wasn't supposed to happen by the books".[32] This meant that the project would not need to start separate breeding programs for each geographic region of the planet.
 
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acespicoli

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DLI Terminology:​

PHOTOPERIODISM: The physiological growth or reproduction response of a plant when exposed to a specific photoperiod or day length and the corresponding period of darkness.

DLI: Daily Light Integral refers to the total number of PAR photons, delivered to a square meter area through the course of a 24-hour period. It is expressed as moles of light (mol) per square meter (m−2) per day (d−1).

PPFD: Photosynthetic Photon Flux Density as measured in micromoles per second, per square meter(μmol/m2/s) is a snapshot of all PAR light falling on a surface within a single second.

Daily Light Integral Maps:​

US Daily Light Integral DLI Map -Albopepper
These maps show the average DLI across the United States for each month of the year. (click to enlarge) Save
U.S. DLI MAPS: Researchers from Purdue University have analyzed the solar radiation levels over a 14 year period. This data then allowed them to compile DLI maps all across the United States. Daily light integral varies significantly depending on latitude and other geographic factors. But the light levels also change dramatically depending on the time of year.

To properly depict the fluctuation in DLI across both space and time, 12 monthly DLI maps for the lower 48 states can been seen above. As plants assimilate solar radiation, this directly drives plant growth. Different plant types have different DLI requirements for optimal health. This is why horticulturists and commercial growers pay very close attention to this metric.

You can check here to seen an interactive version of these maps: U.S. Daily Light Integral Map

Daily Light Integral Chart:​

Daily Light Integral DLI Chart -Albopepper
This daily light integral (DLI) chart shows the relationship between photoperiod and PPFD. (click to enlarge) Save
The daily light integral chart shown above is colored coded using the exact same values as the US DLI map. This allows you to quickly compare artificial grow light settings to the natural sunlight exposure that outdoor plants receive.

For example, in Pennsylvania, in April, the average DLI is between 30 and 35. By looking at this DLI chart, you can determine the light intensity that would be needed to match typical outdoor levels. By scanning the chart, you can see that a 14 hour light cycle would require PPFD levels between 600 to 700 μmols.

Daily Light Integral for Plants:​

To maintain optimal plant growth, it's important to provide adequate light levels as measured by the DLI. What DLI levels do plants really need? Unfortunately, there's no simple answer to that question. Different plant types are adapted to different light intensities. Some low light plants like lettuce have much lower requirements. On the other hand, high light plants such as tomatoes have much higher requirements for peak production.

Purdue University has put out some great information, including their own daily light integral chart. This DLI chart is plant-specific. It lists many greenhouse crops, showing the minimum DLI levels that the plants would need to achieve an acceptable quality of growth.

Seedlings & Herbs Grow Indoors Under Dimmable LED Lights

These dimmable LEDs are an excellent way dial in the perfect PPFD levels without needing to alter the hanging height.
ADJUSTING FOR DLI: If necessary, the light intensity can be boosted by placing your lights closer to the plants. Alternatively, increasing the duration of the light cycle is a second option. Both approaches effectively raise the DLI and boost plant growth!

Of course, when plants are getting too much light the reverse applies. Raising lights might solve the problem. This may increase your coverage area, allowing you to grow more plants. Or you can decrease the PPFD levels by dimming your light source. Reducing the light cycle is also advantageous due to the reduction in power consumption. Ideally, a grower will want their plants to yield more mass per watts consumed. That's why it's so important to understand how all of these metrics relate to each other.

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If there's one question that never allows a cannabis grower any sleep, it's — are my plants getting enough light?

If this question has ever crossed your mind, don't worry, you're not alone. Considering every professional-grade marijuana grow facility is decked out in ultra-powerful lighting, it's no mystery why many home growers find their lighting solution inadequate.

Luckily for you, your cannabis crop’s success isn't dependent on the size of your lights. Instead, the health of your marijuana plants in regards to lighting relies on a parameter known as the daily light integral or DLI for short.

Read along as we describe recommended DLI values for cannabis from seedling, to vegetative, to flower (a.k.a. bloom), to harvest. You'll learn what the DLI is, how it affects plants, how it can save you money, and how you can optimally use your grow lights by measuring and adjusting the DLI.

Contents​

A Brief Recap on DLI​

As we've previously described what the DLI is, let's take this time to briefly recap the fundamental points regarding the DLI.

💡
The daily light integral (DLI) is the total sum of photosynthetic lighting intensity measured as PPFD over a 24 hour period. In short, the DLI is a measure of usable light your plant receives over a day. Ultimately, supplying adequate light intensity and duration (i.e. the DLI) is the single most important factor when it comes to plant lighting.
The important part about plant lighting is that each plant has a maximum DLI in its respective growth stage. Thus, the DLI serves as a measurement that provides cultivators insight into the amount of usable light that a crop needs to flourish. Luckily, the effects of DLI on plants is well researched for many plants and we can harness this knowledge to cultivate cannabis better and cheaper.

The Effect of DLI on Plants​

The effect of the DLI on all plants is monumental. Without proper lighting, plants would have a tough time surviving. As we can see, plants throughout the world have adapted their lighting needs according to their environment.

Now, here's a list of effects of supplying proper amount of light on plants:

  • Reduces node spacing
  • Stimulates root and shoot growth
  • Increases stem thickness
  • Increases flower size
  • Increases plant vigor
  • Increases nutrient and water uptake
  • Reduces susceptibility to disease and pest outbreaks
  • Increases growth in general
As you can see, the DLI measure affects the entire plant — not just the leaves. Supplying your cannabis plants with proper lighting is the #1 factor for a successful marijuana crop.

DLI for Cannabis​

Now, let's talk specifically about cannabis plants and DLI.

Whether you grow marijuana indoors or outdoors, understanding the relationship between light and cannabis plant age is essential for a successful grow cycle leading to big, healthy buds and a bountiful harvest.

If you're mainly growing autoflowering cannabis, we recommend to read our article that is focused in lighting for autos after this one. All principles described within this article apply for autos as well.

Cannabis Lighting: PAR / PPFD And DLI For Autoflowers
If you’re wondering what grow lighting your autoflowering cannabis strains need to flourish, this article is for you. We’ve put together everything you need to know to optimally set your PPFD and DLI levels.


What's The Optimum DLI For Cannabis Plants Over The Full Grow Cycle?​

As cannabis originated from southern and mountainous areas such as Nepal, Afghanistan, Pakistan, and more it prefers a lot of light and thus, recommended DLI values are relatively high.

In agricultural terms, cannabis plants require full-sun to flourish. Indoors, however, cultivators must consider the light height, light output, and lighting duration to achieve proper lighting.

Based on research and experience, we’ve broken down ideal DLI values for cannabis plants over the length of the full grow cycle:

cannabis-dli-cycle.png
The optimal DLI over a full cannabis grow cycle from seedling (or clone for that matter) to harvest Pin It Pin It
As you can see, cannabis seedlings or clones require less light, whereas a cannabis plant flourishes when supplied with a lot of light in its vegetative (veg) and flowering (bloom) stage. Providing the plant with too much light too early will result in damage, as it needs time to adjust to higher light intensities. To initiate the flowering period, the lighting duration is reduced significantly (typically from 18 hours down to 12 hours), which also results in a lower DLI. Light intensity is then gradually increased to get big buds. Providing such a high DLI with just about 12 hours of lighting requires a strong grow light able to supply a high PPFD.

💡
As the ideal cannabis DLI requirement changes from week to week, we recommend measuring and adjusting DLI repeatedly and regularly.
Cannabis growth can be increased even further if additional CO2 is added to the grow space. As this is a bit of an advanced topic, it is described in more detail a little later within this article.

Cannabis growers can achieve an optimal DLI value by understanding the basics of choosing the right grow light and the correct positioning for indoor grow lights.

DLI For Cannabis Autoflowers​

Autoflowering cannabis (also called day neutral cannabis) varieties automatically switch from vegetative growth to the flowering stage based on age, as opposed to the ratio of light to dark hours required with regular, photoperiod dependent strains. As for the DLI, this means that the plant can be considered to be in the vegetative stage even when flowers are present. Therefore, no flowering phase is initiated by the light schedule and DLI levels of over 40 mol/m²/d can be kept until the plant is harvested.

cannabis-dli-cycle-autos.png
The optimal DLI over a full autoflowering cannabis grow cycle from seed to harvest Pin It Pin It

Cannabis PPFD Range​

Providing ideal immediate PAR intensity (measured in PPFD) to your cannabis plant is just as crucial as providing the optimal amount of light throughout the day. As the DLI is the product of time (photoperiod) and light intensity (PPFD), you can hit an optimal DLI value with the wrong combination of those two parameters (e.g. when you have very bright lights but only on for an hour). We’ve written an in-depth article about cannabis PAR levels that dives deeper into the topic. To keep it simple for now, we recommend the following PPFD for your cannabis plant:

Growth PhasePAR Level (PPFD)
Seedling / Clone100 – 300
Vegetative250 – 600
Bloom / Flowering500 – 1050

Cannabis Photoperiod​

To progress the cannabis plant through its vegetative and flowering stage, different lighting durations, so-called photoperiods, are required to simulate the season’s natural rhythm. In general, you want to keep your lights on for as long as possible, but also need to create a drastic shift when initiating the flowering period. Common cannabis photoperiods are 18 hours for the vegetative phase and 12 hours for the flowering phase. There is a range however, and you can adjust your lighting to fit into it. We recommend to keep your lights on for the following duration:

Growth PhasePhotoperiod (h)
Seedling / Clone16 – 24
Vegetative16 – 24
Bloom / Flowering10 – 13
Maturing10 – 14
Mind that the flowering period is not required for autoflowers per-se, as they flower based on an internal clock. Therefore, you could keep the lights on for longer to achieve a higher DLI with lower PPFD. Keeping a photoperiod of 20 h is a good place to start when growing autoflowers.

Cannabis DLI Calculator​

We know that cannabis lighting can be complex and maybe even overwhelming. To make your life as a grower easier, we created our cannabis DLI calculator that uses the knowledge supplied in this article to calculate a recommendation for your grow lighting.

Increasing Yields with CO2​

Photosynthesis mainly requires photons (light), water and CO2. As for really maxing out the rate of photosynthesis, all plants do have a point where more light and water just does not equal more growth, but more often than not, inadequate CO2 supplementation is the primary limiting factor.

cannabis-co2-ppfd.png
Influence of CO2 concentration on the rate of photosynthesis Pin It Pin It
General indoor CO2 levels of about 400 to 600 ppm quickly restrict photosynthetic activity to less than half of what would be possible. Supplementing higher CO2 to at least 800 ppm greatly boosts photosynthetic activity and allows for more light or rather higher PAR levels. If you really want to max out your cannabis plant’s growth, we recommend the following CO2 levels:

Growth PhaseCO2 Level (ppm)
Seedling / Clone400
Vegetative400 – 800
Bloom / Flowering800 – 1400
Adding CO2 to your cannabis grow is a science of its own. If you want to dive deeper into this topic, we recommend our article on exactly that.

Look At What Your Plants Tell You​

It’s important to note that all of the research on cannabis DLI, cannabis PAR levels, cannabis CO2 and every other lighting aspect won’t be able to exactly cover the needs of your specific plants in your individual setup. There are many other factors such as the grow room temperature, spectral light distribution, amount and quality of water, nutrients, cannabis genetics, and many more that have an influence on how well your marijuana plants grow.

We recommend treating all the aforementioned values and ranges as a basic guideline to act as a starting point for optimizing the lighting of your individual plants. If they seem happy and healthy, you’re definitely on the right track!

The Economic Benefit of an Optimal DLI​

Most indoor cannabis growers, or indoor horticulturalists, for that matter, have yet to discover the economic benefits they can get when optimizing their lighting.

Since each plant, such as cannabis, requires a specific DLI for optimal growth one can assume that going over or under the recommended DLI will cause a disproportionate economic impact on your wallet.

DLI-and-Effeiciency@2x-2.png
Increasing the DLI does not increase plant growth indefinitely – even the opposite Pin It Pin It
Many marijuana growers pay an unnecessarily high electricity bill because there's a common belief that the more light — the bigger the buds. This, however, couldn't be further from the truth. The more light is not always the better: There is a point where more light does not induce more plant growth or even causes harm to the plant. On the other end, having a lower than recommended DLI results in lackluster buds, and a missed growing opportunity.

💡
In other words, there is a sweet spot that you want to hit that encompasses maximum plant growth with minimal DLI so your indoor growing operation won't produce a bigger electricity bill than you bargained for.

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Front. Plant Sci., 26 September 2022
Sec. Crop and Product Physiology
Volume 13 - 2022 | https://doi.org/10.3389/fpls.2022.974018

Indoor grown cannabis yield increased proportionally with light intensity, but ultraviolet radiation did not affect yield or cannabinoid content​

 
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acespicoli

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Intensity and Spectrum: The Role of Lighting in Vapor Pressure Deficit​

August 24, 2023
By Hannia Mendoza-Dickey
Robert Manes
View All
Publication
Article

Cannabis Science and TechnologyJuly/August 2023
Volume 6
Issue 6
Pages: 22-30

This article delves into the aspects of horticultural light intensity and spectra as well as their relative influence on cannabis photosynthesis, photomorphogenesis, and overall yield.

This article delves into the aspects of horticultural light intensity and spectra as well as their relative influence on cannabis photosynthesis, photomorphogenesis, and overall yield. While the manipulation of lighting spectrum and the utilization of sufficient photon density can govern the expression of both major and minor cannabinoids, as well as secondary metabolites such as an array of terpenes, anthocyanins, and flavonoids; these important environmental factors exert considerable influence on plant transpiration and thus a plant’s physiological response to vapor pressure deficit (VPD). In the rapidly expanding cannabis industry, optimizing cultivation practices to maximize crop quality and yield hinges upon a cultivator’s understanding of the intricate interplay between various lighting modalities and VPD. In turn, correct management of VPD alleviates many of the problems that plague controlled environment agriculturists, such as nutritional deficiencies, mold, mildew, and waste of valuable resources, such as CO2, water, and nutrients—the latter of which also results in undesirable capital expenditures.
The art of cannabis and hemp cultivation is reliant on achieving a balance between utilizing stable genetics and the meticulous optimization of various environmental parameters. These factors synergistically contribute to the cultivation outcome, influencing the production of optimal yield and phytochemical composition of the plant varietals involved. To this point, vapor pressure deficit (VPD) emerges as a metric of paramount importance to the overall success of the cultivation environment. VPD is a measurement that represents the deficit between the amount of moisture in the air and the maximum moisture the air can hold (saturation). This metric exerts a profound impact on the transpiration rate within cannabis plants. Transpiration is a physiological process involving the transport of water (along with CO2 and dissolved nutrients) from the roots through the xylem to the leaf (stomata), where it undergoes a phase change into vapor and is subsequently released into the atmosphere.
Although transpiration is primarily driven by the vapor pressure within the plant, it’s important to note that the internal atmosphere of the leaf is not saturated. However, the stomata, which are tiny pores on the leaf, play a crucial role in pressure regulation and thermoregulation. The stomata serve as a gateway between the highly humid internal environment of a plant and the surrounding atmosphere. When humid and dry air come into contact, they attempt to balance each other out, with vapor pressure flowing from high humidity to low. Therefore, if the atmosphere is very hot and dry, water vapor will escape from the leaves at a faster rate, increasing the transpirational demand on cannabis plants and potentially leading to wilting and nutrient deficiencies (see Figure 1a). Conversely, in humid grow rooms where atmospheric conditions are not significantly different from those of the leaf, less water vapor will be able to escape—giving rise to various issues, including the development of fungal diseases, mold, and root rot (see Figure 1b). When the VPD is at an optimal level, plants can more effectively absorb and distribute the nutrients they need for growth and yield (see Figure 1c). Scientifically-minded growers favor VPD as a measure that provides insight in the ever-changing conditions of the air’s moisture-holding capacity at any given temperature.

The end results of different VPD conditions


How to Calculate for VPD in Your Cultivation Environment​

The Alduchov and Eskridge equation is an improved form of the Magnus’ formula and is commonly used to estimate the saturation vapor pressure (SVP) and VPD in meteorology. The VPD represents the difference between the saturation vapor pressure (es) and the actual vapor pressure (ea) of the air.
The Alduchov and Eskridge equation for calculating es is as follows in Equation 1:
image


where es is the saturation vapor pressure in kilopascals (kPa) and T is the temperature in degrees Celsius (°C).
To calculate the VPD, you need to know both the saturation vapor pressure (es) and the actual vapor pressure (ea) of the air. The VPD is then given by Equation 2:
image


For example, assume the temperature (T) is 25 °C and the actual vapor pressure (ea) is 2.5 kPa. We will calculate the saturation vapor pressure (es) and the VPD. Using the Alduchov and Eskridge equation, we can calculate the saturation vapor pressure (es)
as follows:

es = 0.6108 * exp[(17.27 * 25) / (25 + 237.3)]


es ≈ 3.17 kPa

Now, we can calculate the vapor pressure deficit (VPD) using the given actual vapor pressure (ea):

VPD = es - ea


= 3.17 - 2.5


≈ 0.67 kPa

In this example, at a temperature of 25 °C, theSVP is approximately 3.17 kPa, and the VPD is approximately 0.67 kPa.
Understanding VPD is crucial for optimizing plant growth and determining appropriate environmental conditions in various applications, including greenhouse cultivation, where maintaining an optimal VPD range is critical for maximizing crop productivity
and quality.
Figure 2 illustrates the recommended VPD levels for cannabis and hemp plants in vegetative stages. Within this chart, the dark green region (0.9-1.1 kPa) represents the most favorable VPD for cultivating cannabis plants. The light green area represents VPD ranges (0.7-0.9 kPa and 1.1-1.3 kPa) that are slightly outside of optimal range yet remain highly desirable. The yellow region indicates VPD levels that require adjustment to achieve optimal plant growth. Lastly, VPD values falling within the white range, lower than 0.5 kPa and higher than 1.7 kPa, are considered detrimental to the overall growth of the plants and require immediate correction.

Recommended VPD levels for plants in the vegetative state


Figure 3 represents recommended atmospheric VPD values for cannabis or hemp plants in the flowering stage. The green section is the VPD sweet spot and represents the most desirable atmospheric conditions for cannabis cultivation. Purple indicates VPD fringe ranges, but is still more than acceptable. Orange represents VPD conditions requiring adjustment. VPD falling within the white range is detrimental to plant function.

Recommended VPD levels for plants in the flowering stage


Conversely, the borderline transpiration zone (orange) denotes both elevated and low VPD values ranging from (1.7–2.3 kPa and 0.7–1.0 kPa), respectively. In the elevated orange zone, plants may experience accelerated water loss, increased stress, and lower transpiration rates. In the lower orange zone, plants may experience low transpiration, higher humidity, and may experience mold and mildew issues. The danger zone (white) represents extremely high or low VPD values outside the recommended ranges. Values below 0.4 kPa or above 2.3 kPa indicate potential severe transpirational issues such as excessive humidity levels or nutrient deficiencies due to high transpiration rates and should be corrected immediately.

Why a Lower VPD in Vegetative versus Flower?​

For plants in vegetative stages, root mass and stem structure are immature and have relatively little mass. The plant is focusing almost all of its resources to build these two components. Leaves with stomata are few, at least in the early stages of vegetation. A smaller root system contributes less root pressure to the plant system. Lower VPD exhibits more control over water and nutrient uptake for this stage of growth. A more controlled transpiration rate and less water loss occurs, minimizing water and nutrient stress.
During the flowering stage, the root system should be quite large and robust and root pressure should be high. Overall, plant mass during flower is many times that of plants in the vegetative stage of growth. Leaf area will be extensive and as flowers develop, water, CO₂, and nutrient demand will be significant. A higher VPD will provide for greater transpiration to satisfy the plant’s needs. However, it is important to note that extremely high VPDs can result in lower nutrient absorption and many growers increase nutrient levels to compensate. This can result in higher nutrient costs. In addition, higher transpiration may make plants more susceptible to mold, mildew, and root rot. Extremely high VPD may cause stomata to close to preserve resources, which demonstrates the undesirable side-effect of stunting growth.

What Role Does Lighting Play in the VPD Equation?​

Horticultural lighting, such as full-spectrum light emitting diode (LED) fixtures impact VPD indirectly by affecting the temperature and humidity in the growing environment. It is a common misconception that LEDs produce very little, or no, heat at all. This is incorrect. LEDs apply less heat to the plants than other technologies if the luminaire and facility thermal management systems are well designed (1). Most LEDs used for illumination purposes convert approximately 22–28% of input power into light that can be used by the plant. To the contrary, high intensity discharge (HID) lighting, such as high pressure sodium (HPS), ceramic metal halide (CMH), and metal halide (MH) lamps convert only 5–10% of their energy consumption into usable light. The rest of the input power for both HID and LED lighting is converted into infrared light (IR), which is felt as heat. Interestingly, HID lighting converts this energy into IR at the lamp (light bulb) itself, while LED waste heat is produced at the silicon junctions of the diodes (1). A properly ventilated LED luminaire will move this thermal radiation away from the plant as the heat rises, whereas HID lighting radiates this IR directly to the plant leaves. Additionally, HID horticultural lighting typically uses non-flammable metallic “hoods” to reflect light towards the plants, which further collects this IR and directs it at the leaves themselves. The bottom line here is that both technologies produce heat that greatly affects VPD, albeit LEDs present significantly less impact on transpiration issues due to lower leaf temperatures and lower VPD than their HID counterparts.

The Influence of Lighting Spectrum on VPD​

Lighting spectrum also affects VPD. Red light (~630–760 nm) is known to promote stomatal opening, increasing transpiration rates and potentially elevating VPD. Blue light (wavelengths around 400–500 nm), on the other hand, can have a suppressive effect on stomatal opening, which may reduce transpiration rates and subsequently lower VPD. However, both blue and red light used simultaneously and in the correct ratios can increase VPD dramatically (2).
White LEDs present a unique variable to VPD manipulation. Most LED luminaires on the global market use “full spectrum” white LEDs (Figure 1d). This full spectrum is created by coating a discrete high-intensity blue LED, commonly peaking at 450 nm, with a specially formulated phosphor. When this phosphor is excited by the output of the blue LED, it fluoresces and produces light across a broad spectrum. Since this blue LED’s base frequency (450 nm) is the source of most of the spectral energy produced, its amplitude is usually significant compared to the rest of the spectral radiation produced by the LED. Addition of any supplemental red (discrete) LEDs must take this into account to optimize crop yield and phytochemical production (1).
In plants, red light is primarily detected by phytochrome Pr (phytochrome red) and Pfr (phytochrome far red) photoreceptor proteins, whereas blue light is detected by the photoreceptor proteins cryptochromes and phototropins. The interaction of these phytochromes initiate a signaling cascade within the plant cells, ultimately leading to convergence of these protein signaling pathways, activating ion channels, which changes guard cell turgor pressure (3).
Guard cells are specialized and found in the epidermis of plant leaves and stems. When they are filled with water, or turgid, they stretch the epidermis and create openings in the stomata. When they deflate, the pressure on the plant epidermis is lessened and the stomata close. This opening and closing regulates gas exchange in transpiration and allowing CO2 to enter via the stomata. Guard cell water pressure is controlled by ion movement, specifically, potassium and chloride ions, across the cell membranes. Pumping these ions out of the guard cells causes water to also escape, deflating the guard cells (4,5).
Ion channels are protein channels residing in the cell membranes and they come in two configurations: gated channels, which are triggered by specific stimuli, such as voltage, chemicals, force, and temperature; and open channels, which as you might have guessed, stay open and serve as baseline or “leakage” channels. Upon exposure to red light, phytochrome photoreceptors activate signaling pathways that open potassium ion channels, allowing potassium ions to increase cell pressure and open stomata. The addition of blue light to this red light stimulates ion channel activity, thus increasing stomatal response (6).
Ion pumps use adenosine triphosphate (ATP, the cell’s energy currency) to transport ions across cell membranes. The pumps help maintain cell function, signaling, pressure balancing, and other physiological cell functions. Both red and blue light stimulate changes in ion concentrations and membrane potential that help manage cellular processes (7).
Collectively, the optimal ratio of red to blue light for stomatal opening can vary among different plant species, as well as stage of growth. Some plants exhibit a higher sensitivity to red light especially during flowering, while others have a greater requirement for blue light, especially during propagation and vegetative stages. Determining the ideal balance of red and blue light for specific plant species can maximize the stomatal response, thus having a profound impact on finding the optimal VPD window.

Conclusion​

By and large, the ongoing advancements in lighting technology continue to revolutionize indoor cannabis cultivation. Specifically, the importance of lighting spectrum and VPD cannot be overstated in aiming to achieve optimal growth and yield results. Fine tuning the spectral composition of light and maintaining an appropriate VPD within the cultivation environment are vital considerations for growers aiming to maximize their crop's potential. The interplay between red and blue light wavelengths, for instance, impacts the overall VPD, which in turn influences transpiration rates, stomatal conductance, and overall plant health. In simpler terms, maintaining consistent temperature and relative humidity in the cultivation space directly impacts the VPD, which in turn affects plant transpiration and growth. Consequently, a comprehension of the intricate relationship between lighting factors and VPD dynamics is indispensable for cultivators seeking to achieve exceptional outcomes in their cannabis production endeavors.

References
  1. Manes, R. and Stumpf, T., How to Grow Marijuana with LEDs.1st ed., 2019.
  2. Inoue, S. and Kinoshita, T., Blue Light Regulation of Stomatal Opening and the Plasma Membrane H+-ATPase. Plant Physiology, 2017, 174(2), 531–538.
  3. Assmann, S.M. and Jegla, T., Guard Cell Sensory Systems: Recent Insights on Stomatal Responses to Light, Abscisic Acid, and CO2. Current Opinion in Plant Biology, 2016, 33, 157-167.
  4. Shimazaki et al., Blue light activates the plasma membrane H+-ATPase by phosphorylation of the C-terminus in stomatal guard cells, The EMBO Journal, 2007.
  5. Mott et al., Blue light inhibition of guard cell anion channels mediated by abscisic acid, Plant Journal, 2008.
  6. Hille, B., Ion Channels of Excitable Membranes, 2001, 3rd ed.
  7. Alberts et al., Molecular Biology of the Cell, 2002, 4th ed.

About the Authors

Dr. Zacariah Hildenbrand is a research Professor at the University of Texas at El Paso, the principal founder of Inform Environmental, a partner of Medusa Analytical, and is a director of the Curtis Mathes Corporation (OTC:CMCZ). Hannia Mendoza-Dickey is an MS Chemistry student at the University of Texas at El Paso. Robert J. Manes is with Curtis Mathes Corporation.
Direct correspondence to: zlhildenbrand@utep.edu.

How to Cite This Article
Mendoza-Dickey, H., Manes, R., Hildenbrand, Z., Intensity and Spectrum: The Role of Lighting in Vapor Pressure Deficit, Cannabis Science and Technology, 2023, 6(6), 22-32.
 
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acespicoli

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EC in water when feeding cannabis​

Plants need the best care to grow strong and healthy. One of the most important factors is the EC of the irrigation water. Therefore, it’s essential to monitor the EC level of the irrigation water. In this post, we want to clarify everything about the ideal EC level for cannabis.
Contents

What is EC in water?

EC, or electrical conductivity, is the ability of a liquid to conduct electricity. However, water doesn’t conduct electricity by itself, but rather depends on the amount of minerals it contains. Water with a good mineral content conducts electricity just like a wire. However, distilled water (H2O) does not.
EC allows us to measure the amount of minerals in the water to determine if it conducts electricity well and if it is suitable for plants.
For this reason, EC levels need to be ideal in your cannabis crops. The balance and concentration of nutrients in the soil and water are crucial for a grower, preventing issues like nutrient deficiencies or excesses. A plant may not recover from nutrient lockout or an overload of nutrients.

Effects of high or low EC levels in crops

A distinctive trait of plants is their sensitivity to EC. It’s not sensitivity to electricity itself but rather to the mineral content in the water. The more fertilizer the water contains, the more electricity it will conduct, which can be checked with an EC and pH meter.
However, your plant might encounter difficulties in absorbing water with too many minerals. Due to the liquid’s high density, the roots may struggle to filter it properly, potentially causing problems.

High EC

The ideal EC for cannabis is easy to calculate, and once you know it, you can assess what is happening with your plant. When the plant is exposed to high EC levels, it can’t absorb the nutrients, leading to a blockage. That’s why the ideal EC levels are crucial for cannabis to properly absorb all nutrients.

Low EC

In cases where EC is low, the plant is forced to absorb more water through its roots. This causes the roots to expand to increase their capacity and take in more nutrients. Additionally, it’s easier for a plant to recover from low EC levels than the opposite.
Cannabis tolerates certain levels of water density. You can start watering with osmosis or distilled water and add specific nutrients to make better use of the fertilizer used. If you use tap water, your crop may not be able to absorb all the fertilizer it needs due to the water’s density. This can cause nutrient deficiencies and an increase in unabsorbable mineral salts in the soil, like lime and sodium. Such a situation means that each time you water, the plant won’t be able to absorb the nutrients, leading to root blockage.

How to regulate EC levels in cannabis cultivation

EC in cannabis and absorption

When regulating EC levels, it’s important to consider the required levels for each stage. These are:
  • During the first 15 days after germination, the ideal EC for cannabis is between 0.5 and 0.8.
  • Progressively, increase the levels to 1.2 by the end of the growth phase.
  • During the flowering stage, the EC should increase as the plant will need more nutrients, establishing EC between 1.2 and 1.6.
  • In the fattening phase, increase EC to 1.8/2.1. This will be the maximum level.
To increase EC levels, simply add more fertilizer to the mix or change the nutrient solution for one with higher nutritional content.
The most common mistake novice growers make with EC is only measuring the water they are about to use for irrigation. The important EC values are those in the soil, as this is where the plants feed from. To measure EC levels when growing in soil, in addition to measuring the irrigation water, you should let the plant drain a bit of water and measure that runoff. This will tell you if the plant is getting enough nutrients or if the soil is overloaded.

EC Meters

An important factor in controlling EC is measuring it as accurately as possible. For this, EC meters are essential.
EC meters are electronic devices composed of two parts, either attached or separate: a probe and an electrode. The electrode is responsible for calculating the conductivity of a liquid to determine the EC values, and it also measures temperature. It’s recommended to calibrate the meters for their first use and after each measurement to avoid errors.
There are two main types of meters:
  • Portable meters are perfect for small or soil-based crops. They are very easy to use and don’t require much knowledge, like the Adwa EC meter. These meters have high precision, and most allow you to measure both EC and water temperature for better control of your crop.
  • As for continuous meters, they are usually mounted on the wall or another convenient surface, like the Adwa continuous wall-mounted EC meter. These meters are perfect for coco or hydroponic crops. You simply submerge the probe in the water and plug it into the meter. They provide 100% precision, and it’s recommended to calibrate them at least once a month. With proper cleaning and calibration, these meters can last a long time.
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Knowing the ideal EC for cannabis is crucial, as along with pH, these are the key indicators of water quality. By maintaining these levels as recommended, your plants will grow healthy and strong
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Front. Plant Sci., 18 September 2023
Sec. Plant Metabolism and Chemodiversity
Volume 14 - 2023 | https://doi.org/10.3389/fpls.2023.1233232
This article is part of the Research TopicEnvironmental and Agronomic Factors affecting the Chemical Composition and Biological Activity of Cannabis ExtractsView all 8 articles

Cannabis Hunger Games: nutrient stress induction in flowering stage – impact of organic and mineral fertilizer levels on biomass, cannabidiol (CBD) yield and nutrient use efficiency​

 

acespicoli

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Mentor
Should be pretty simple to calculate a rough estimate, if I'm remembering my chemistry correctly. The formula for fermentation is:

C6H12O6 → 2 CH3CH2OH + 2 CO2

So, we should get the same quantity of ethanol molecules as CO2 molecules. If a "standard" 5 gallon batch is 5% ABV, that's equivalent to 0.25 gallons, or 0.95L of ethanol. Ethanol's density at 20C is 0.78945 kg/L, so we'd have 0.75 kg (750g) of ethanol in a 5g batch. Ethanol's molar mass is 46.07 g/mol, so we should have a total of about 16.3 moles of both ethanol and CO2 produced. 16.3 moles of CO2, at SATP, would have a volume of 24.8L * 16.3 = 404.2 liters of CO2, weighing a total of around 717g (about 1.58 pounds).

404 liters is a lot, but not that much. 106 gallons, or a little more than most bathtubs hold.

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acespicoli

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1736878200428.png

The schematic, screenshots of representative resources and a user case of CannabisGDB. (a) The flow diagram showing design and construction of CannabisGDB. (b)The home page of CannabisGDB. (c)The ‘varieties module’ providing summary of cannabis genomes, detailed information of cannabis varieties and genome browser tool. (d) The ‘gene loci module’ showing detailed information of genes identified in this study. (e) The ‘metabolites module’ providing chemical phenotypes in various cannabis varieties. (f) The ‘proteins module’ presenting information of experimentally identified proteins. (g) A case study for the application of CannabisGDB. Dashed lines indicate linkages between different pages.

Plant Biotechnol J. 2021 Feb 4;19(5):857–859. doi: 10.1111/pbi.13548

 
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