CAM photosynthesis

[TorturedSoul]

I just figured the PAR was better with mh even though the listed lumens are higher on hps

And that's a funny thing. As far as I know, you are correct - and the second part of your statement gives evidence to it. But I saw higher yields when I started flowering under HPS. Then I ended up donating the MH to someone and running the HPS all the way through - and still saw higher yields.

It was a long time ago, and it seems reasonable to assume that I learned things between the beginning and end of that time. But it was the same strain and method of growing, so... IDK. Maybe "quantity" has a quality all its own, lol.

 

[TheFertilizer]

I am a fan of mh for the entire cycle. I just figured the PAR was better with mh even though the listed lumens are higher on hps

I think Hortilux and Ushio have blue enhanced HPS lamps. I ordered an Ushio but it came dead on arrival

I've been liking the results under my 3100K CMH so far. They have 4200K varieties that are pretty high on the UV scale as well.

 

[bobrown14]

Interesting discussion. I think now that I've been watching my temp and RH a lot closer that getting in the CAM sweet spot with temps and the plants transpire a lot more raising the RH in my flower room.

I've got close to a full house now so its pretty noticeable specially with room door closed. RH climbs up to about 65-70RH @ 80F it will stay there. Seems like plants are drinking a lot of water too. As soon as I open the door and let out some RH into the rest of the house, the plants seem to transpire less. Temps drop (70F) and RH drops way down (40-45RH) as well.

 

[Dusted]

I started this to hypothesize that our plants could be using CAM photosynthesis in addition to regular photosynthesis:

Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions. In a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2).

CAM plants include most succulents, such as cacti and agaves, as well as someorchids and bromeliads.

To summarize:
-I have documented a twice daily transpiration cycle, Maximizing at midnight ( CAM) and midday (regular photosynthesis).
-Blue light (metal halide) causes stoma to open during the day (regular photosynthesis)
-The sugar leaves of Cannabis flowers take on a thick succulent appearance, particularly when getting close to hid lights (CAM photosynthesis) nearing maturity.
-Some Cannabis plants have evolved to grow under extremely arid conditions (Hindu Kush mountains) (CAM photosynthesis)

I didn't get to monitor the transpiration rates during vegetative growth but it will be interesting to see if the nightly transpiration cycle is lower than during flowering. As I get closer to harvest and the fan leaves are removed the night transpiration should increase over day transpiration.

 

[bobrown14]

I didn't get to monitor the transpiration rates during vegetative growth but it will be interesting to see if the nightly transpiration cycle is lower than during flowering.

As I get closer to harvest and the fan leaves are removed the night transpiration should increase over day transpiration.

Question - how are the fans being removed?

How do plants transpire more at night without lights on? I though transpiration is used to cool the plants during photosynthesis (lights on).

My flower room has higher RH at lights on IF I didn't have ventilation. With large flowering plants daytime is pretty hot and humid without any ventilation. When they are smaller or in VEG, nighttime is cooler with higher RH.

 

[Dusted]

I am in the final weeks of this grow. Since the fan leaves were getting deficient and yellowing I removed all of the ones I could get to. The RH logs show a definite swing to night time transpiration over daytime since the leaves were removed. It’s hard to measure the volume of water used daytime vs night in the reservoir since the volumes are way down. One more confirmation of my theory that Cannabis is a facultative CAM photosynthesizer. I will monitor the vegetative stage of my new grow for more data

 

[TheFertilizer]

One of the things about CAM carbon fixation to keep in mind is that they are not photosynthesizing at night. They're building up the acid during the night, and will use the acid in the place of carbon during the day to photosynthesize. Photosynthesis never happens in the absence of light.

I have only ever really seen cannabis debated to be either C3 or C4. Most people tend to think it's C4 because it handles drought and high temperature so well, but I read a study that said C4 plants barely respond to increase CO2 in the atmosphere because they're already so efficient at fixing carbon. Cannabis on the other hand is well documented to respond to increased CO2 concentrations, which suggests it's a C3.

The other thing to consider is C4 and CAM plants are extremely rare. Something like 5% of plant species worldwide are C4, and I believe even less than that are CAM. So basically 95% of any plant species are C3; that includes very close relatives to cannabis like hops.

But I'm far from an expert either, just took a botany class for a quarter. I had never heard that plants can implement both C3 and C4 carbon pathways before so clearly I don't know everything.

My intuition is just telling me that you can't make these inferences given the environmental factors you're measuring. For one thing, I am not sure that transpiration can be used to directly measure when stomata are open, because many other factors effect transpiration. Secondly, the environmental factors we're discussing are highly dependent upon one another, so any discussion of humidity needs to take into account temperature or it's not an apples-to-apples comparison.

For example, one reason you may observe increased humidity at night is due to the temperature drop vs lights on, and a thing called Vapor Pressure Deficit. Your plants might transpire more at night simply because the VPD is more optimal at night. VPD is determined by the RH and temperature.

It's interesting to me that cannabis might be able to facilitate multiple carbon fixation pathways, but generally speaking I don't think they can prove what type any plant uses without elaborate scientific analysis at the molecular levels; my botany teacher said they actually inject them with markers and watch the carbon pathways on electron microscopes. So far I haven't been able to find any such analysis of cannabis, let alone many varieties. I think the closest we have to scientific evidence of cannabis's pathway is the inferences we can make about it's response to CO2 enrichment--but we don't know what verieties may or may not respond to that.

So with all that said... Maybe you could model an experiment with carbon supplementation. Maybe change the times of day you enrich the atmosphere. If for example you showed CO2 supplementation had an effect at night but not if provided during the day, that would be a telling result for sure.

 

[TorturedSoul]

I have only ever really seen cannabis debated to be either C3 or C4. Most people tend to think it's C4 because it handles drought and high temperature so well, but I read a study that said C4 plants barely respond to increase CO2 in the atmosphere because they're already so efficient at fixing carbon. Cannabis on the other hand is well documented to respond to increased CO2 concentrations, which suggests it's a C3.

The other thing to consider is C4 and CAM plants are extremely rare. Something like 5% of plant species worldwide are C4, and I believe even less than that are CAM. So basically 95% of any plant species are C3; that includes very close relatives to cannabis like hops.

But I'm far from an expert either, just took a botany class for a quarter. I had never heard that plants can implement both C3 and C4 carbon pathways before so clearly I don't know everything.

My impression has always been that cannabis is a C3 species that can function as a C4 one (although perhaps not as well/efficiently). As for its improved efficiency when in the presence of increased levels of CO₂ (with suitably increased levels of both light-energy and temperature)... maybe the plant is a remnant of an earlier era (or has genes from same, which become significant factors under such conditions)? If so, it should do well in the upcoming centuries...

The plant strikes me as being somewhat primitive, although I do not know whether that's actually scientifically true or merely a misconception on my part. If the former is the reality... Is C4, itself, a relic of an earlier age? That could explain why there are so few plant species in that category, I suppose. Again, just speculation on my part - my level of education is less than yours, lol; the only college-level classes I ever had were one microbiology and one natural history class, both evening classes that I attended way back when I was ten (or possibly eleven), which now seems like a long way back indeed, lol.

 

[TheFertilizer]

My impression has always been that cannabis is a C3 species that can function as a C4 one (although perhaps not as well/efficiently). As for its improved efficiency when in the presence of increased levels of CO₂ (with suitably increased levels of both light-energy and temperature)... maybe the plant is a remnant of an earlier era (or has genes from same, which become significant factors under such conditions)? If so, it should do well in the upcoming centuries...

The plant strikes me as being somewhat primitive, although I do not know whether that's actually scientifically true or merely a misconception on my part. If the former is the reality... Is C4, itself, a relic of an earlier age? That could explain why there are so few plant species in that category, I suppose. Again, just speculation on my part - my level of education is less than yours, lol; the only college-level classes I ever had were one microbiology and one natural history class, both evening classes that I attended way back when I was ten (or possibly eleven), which now seems like a long way back indeed, lol.

Actually from what I can find, the C3 pathway is the oldest. I can't find such information to support it, but it seems like CAM is probably the newest.

This article gives a really great explanation of the differences in C3, C4 and CAM plants as well as their distribution and typical environments.

Can Plant Researchers Adapt Plants to Cope with Climate Change?

C3 Plants

• Plants: grain cereals rice, wheat, soybeans, rye, barley; vegetables such as cassava, potatoes, spinach, tomatoes, and yams; trees such as apple, peach, and eucalyptus
• Enzyme: ribulose bisphosphate (RuBP or Rubisco) carboxylase oxygenase (Rubisco)
• Process: convert CO2 into a 3 carbon compound 3-phosphoglyceric acid (or PGA)
• Where carbon it fixed: all leaf mesophyll cells
• Biomass rates: -22% to -35%, with a mean of -26.5%

The vast majority of land plants that we rely on for human food and energy today use the C3 pathway, and no wonder: the C3 photosynthesis process is the oldest of the pathways for carbon fixation, and it is found in plants of all taxonomies. But the C3 pathway is also inefficient. Rubisco reacts not only with CO2 but also O2, leading to photorespiration, which wastes assimilated carbon. Under current atmospheric conditions, potential photosynthesis in C3 plants is suppressed by oxygen as much as 40%. The extent of that suppression increases under stress conditions such as drought, high light , and high temperatures.

Almost all of the food we humans eat is C3, and that includes almost all extant nonhuman primates across all body sizes, including prosimians, new and old world monkeys, and all the apes, even those who live in regions with C4 and CAM plants. As global temperatures rise, the C3 plants will struggle to survive and since we are reliant on them, so will we.

C4 Plants

• Plants: common in forage grasses of lower latitudes, maize, sorghum, sugarcane, fonio, tef, and papyrus
• Enzyme: phosphoenolpyruvate (PEP) carboxylase
• Process: convert CO2 into 4-carbon intermediate
• Where carbon it fixed: the mesophyll cells (MC) and the bundle sheath cells (BSC). C4s have a ring of BSCs surrounding each vein and an outer ring of MCs surrounding the bundle sheath, known as the Kranz anatomy.
• Biomass rates: -9 to -16%, with a mean of -12.5%.

Only about 3% of all land plant species use the C4 pathway, but they dominate nearly all grasslands in the tropics, subtropics, and warm temperate zones. They also include highly productive crops like maize, sorghum, and sugar cane: these crops lead the field for bioenergy use but are not really suitable for human consumption. Maize is the exception, but it is not truly digestible unless it is ground into a powder. Maize and the others are also used as food for animals, converting the energy to meat, which is another inefficient use of plants.

C4 photosynthesis is a biochemical modification of the C3 photosynthesis process. In C4 plants, the C3 style cycle only occurs in the interior cells within the leaf; surrounding them are mesophyll cells which have a much more active enzyme, called phosphoenolpyruvate (PEP) carboxylase. Because of this, C4 plants are those that thrive on long growing seasons with lots of access to sunlight. Some are even saline-tolerant, allowing researchers to consider whether areas which have experienced salinization resulting from past irrigation efforts can be restored by planting salt-tolerant C4 species.

CAM Plants

• Plants: cactuses and other succulents, Clusia, tequila agave, pineapple,
• Enzyme: phosphoenolpyruvate (PEP) carboxylase
• Process: four phases that are tied to available sunlight, CAM plants collect CO2 during the day and then fix CO2 at night as a 4 carbon intermediate
• Where carbon it fixed: vacuoles
• Biomass rates: can fall into either C3 or C4 ranges

CAM photosynthesis was named in honor of the plant family in which Crassulacean, the stonecrop family or the orpine family, was first documented. CAM photosynthesis is an adaptation to low water availability, and it occurs in orchids and succulents from very arid regions. The process of chemical change can be that followed by either C3 or C4; in fact, there's even a plant called Agave augustifolia which switches back and forth between modes as the local system requires.

In terms of human use for food and energy, CAM plants are relatively unexploited, with the exceptions of pineapple and a few agave species, such as the tequila agave. CAM plants exhibit the highest water-use efficiencies in plants which enable them to do well in water-limited environments, such as semi-arid deserts.

Another interesting piece of that article...

Some modifications to C3 plants are thought possible because comparative studies have shown that C3 plants already have some rudimentary genes that are similar in function to C4 plants. The evolutionary process that created C4 out of C3 plants occurred not once but at least 66 times in the past 35 million years. That evolutionary step achieved high photosynthetic performance and high water- and nitrogen- use efficiencies. That's because C4 plants have twice as high a photosynthetic capacity as C3 plants, and can cope with higher temperatures, less water, and available nitrogen. For this reason, biochemists have been attempting to move C4 traits to C3 plants as a way to offset environmental changes faced by global warming.

I think right now, we're still in the "cannabis dark ages" to be able to know for sure if different varieties of cannabis have various different carbon fixation pathways. It's certainly diverse enough to cover the range where C4 plants would be, and as the article states, some plants show genetic similarity to C4 plants. There very well could be C3 AND C4 varieties. The C4 varieties would be much more likely in the tropical phenotypes like sativas, which have a lot of notoriety for growing in similar fashion as the article describes other C4 plants growing.

I asked my botany teacher about all this once, and he said CAM and C4 plants could be found in the same types of dry and arid regions, but the difference is really in their drought-resistance and efficiency in water usage. C4 plants are 4 times as efficient with water as C3 plants, and CAM is 4 times as efficient as C4.


Also to elaborate a little on my CO2 supplementation idea...

I think a way to determine if cannabis is possibly CAM would be to run two of the same strain in separate but identical environments. In one environment, provide CO2 supplementation at night, and in the other make it just atmospheric levels alone.

Since CAM is using the carbon at night to create acid to use in photosynthesis, it will store up the extra CO2 available at night, and increases in photosynthesis should be able to be observed if cannabis can utilize that pathway.

On the other hand, C3 and C4 plants are using the carbon they fix in the photosynthesis process as they get it. If they have access to more CO2 at night, then it shouldn't provide them the ability to do any more photosynthesis than normal, since it would be more CO2 in the absence of light.

The proof that C3/C4 plants don't benefit from extra carbon at night basically lies in the photosynthetic formula.

6CO2 + 6H2O + light energy = C6H12O6 + 6O2

6 parts carbon, + 6 parts water, + light = sugar and oxygen.

The plant uses the sugar for energy, and expels the oxygen as a byproduct. Without the light energy, the sugars cannot be created.

The opposite of that is respiration, which is basically what the plant does for energy in the absence of photosynthesis.

6 parts oxygen + sugar,= 6 parts water and 6 parts oxygen

The byproduct becomes CO2, since the other hydrogen and oxygen atoms are used in the leaf cells for other metabolic purposes. It's essentially when the plant switches to surviving on oxygen in the absence of light.

So if your cannabis plants ( supposedly C3 or C4 ) could somehow make use of that night-time CO2 supplementation, then it would mean it was possible they were using CAM to do so.