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When to have lights on

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GraemeVW

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Maybe an odd question, but im sure i read somewhere that plants will start photosynthesising as soon as there is daylight in the room.
I also read they will only photosynthesis for 12 hours.

If I have my lights on mainly in the evening then the plants have already given up for alot of the high light period.

Does this matter?
Is it even true?
 
erwin123 said:
with certain plants it is easy to tell - eg: Pantanal, because they will start 'closing up' to tell you they are done for the day. So maybe having one or two of those types of plants in your tank may be a good indicator.
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I did write more, but decided to keep my post shorter.

Maybe 1/3rd of my cabomba closes up around 7 ish, when my lights are still on full. They are all fully open way before my lights come on.

I guess, if the plants aren't using the light, then all I'm doing is growing algae.

Even though I like having it lit in the evening, maybe I'd be better off moving the photo period earlier.
Trying to gauge the truth of the matter to see if it matters much.

My main light is programmable so I could still have low light in the evening.
 
GraemeVW said:
Maybe an odd question, but im sure i read somewhere that plants will start photosynthesising as soon as there is daylight in the room.
Click to expand...
Yep.
GraemeVW said:
I also read they will only photosynthesis for 12 hours.
Click to expand...
They photosynthesize as long as light hits them. They may adapt to long photoperiods by closing up early as you observe but they haven’t stopped photosynthesizing, they are just moderating how much light drives them.


If I have my lights on mainly in the evening then the plants have already given up for alot of the high light period.
GraemeVW said:
Does this matter?
Is it even true?
Click to expand...

I mean, some of them look really pretty when they are closed up. You could cut your lights early or reduce light that gets at them before their photoperiod … you can shift their open and closing pattern by adjusting your photoperiod and moderating the amount of light that gets into the tank.

I take it you don’t have an algae issue since your plants are behaving this way … I wouldn’t worry unless you want them to close as you dim your lights … it does look neat.
 
Hi all,
GraemeVW said:
If I have my lights on mainly in the evening then the plants have already given up for alot of the high light period.
Click to expand...
The tanks at home come on about 07:30, so I get a <"quick look before work">, mornings <"aren't a great time for me">, so hopefully I go to work a little bit happier.

Then they have a couple of hours of about midday and then come back on until about 20:30 ish. They are in the kitchen which gets a lot of ambient light, and if I'm home I tend to over ride the time switch so the lights are on all day.

I like a <"12 hour day">, but I'm not too bothered whether that is 10 or 14 hours.

The tanks in the lab. come on at 07:00 and go off at 19:00, without a siesta. This is so I'm occasionally about when the <"lights should be off">.

cheers Darrel
 
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I noticed this morning the cabomba was open by 7.30 with ambient light.

I might move the main light period to match what the plants are showing and just have low light on the evening. It looks live with just a low, central light.
 
www.sciencedaily.com

Plants can tell the time using sugars

A new study has found that plants adjust their daily circadian rhythm to the cycle of day and night by measuring the amount of sugars in their cells.
www.sciencedaily.com
For example, circadian rhythms control the time when plants grow, when their flowers open and release scent, and allow plants to carefully use energy reserves so they do not starve in the night.

Circadian rhythms also help plants to detect changes in the seasons, which is crucial to ensure our crops mature in the correct season.
Click to expand...
Theoretically one should be able to "reset" them to any time period you choose.. again theoretically..
 
JoshP12 said:
They photosynthesize as long as light hits them.
Click to expand...
@oreo57 's post may explain why your experience differs from mine. If circadian rhythms are controlled by sugars created during photosynthesis, then your plants may create sugars for very long period, because they have unlimited access to CO2. While in my low-tech tanks CO2 is (presumably) largely depleted in late afternoon, so the plants have no choice but 'to go to bed'. What do you think?
 
_Maq_ said:
@oreo57 's post may explain why your experience differs from mine. If circadian rhythms are controlled by sugars created during photosynthesis, then your plants may create sugars for very long period, because they have unlimited access to CO2. While in my low-tech tanks CO2 is (presumably) largely depleted in late afternoon, so the plants have no choice but 'to go to bed'. What do you think?
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I like it.

I think there is a difference between growth and photosynthesis though.

If light activated the electron transport chain, the plant will photosynthesize and start making sugar.

Sugar availability will dictate growth.

Certainly, the plant moderates light intake by changing its “shape” … closing up for example to mitigate how much light hits the actual leaves … mine have done this before.
 
Photosynthesis will not be activated by ambient light if it does not exceed the plant light compensation point. Indoor ambient light is typically below LCP and this is why artificial light is needed to grow aquarium plants. So aquarium plant circadian clock is artificial, not measurable by ambient light, but by man made photo period.

The question is whether the artificial circadian clock is cumulative, that is, if there is a siesta period, will the split time be added up.

Closing of Cabomba like plant may indicate the plant has stopped photosynthesis, but opening may not necessarily indicate active photosynthesis, just readiness to begin when the artificial light is on.

A better way to measure photosynthesis is streaming if the plant is under high light. My window sill planted bowl begins streaming when sunlight hit, and slows down or stops instantly when cloud passes by.
 
tiger15 said:
Photosynthesis will not be activated by ambient light if it does not exceed the plant light compensation point. Indoor ambient light is typically below LCP and this is why artificial light is needed to grow aquarium plants. So aquarium plant circadian clock is artificial, not measurable by ambient light, but by man made photo period.
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No, it doesn't work like that.. Below the light compensation point respiration exceeds photosynthesis.
It is not the point of no photosynthesis.
Anyways the wonderful "complication"
www.eurekalert.org

How do plants rest photosynthetic activity at night?

Scientists at Tokyo Institute of Technology have identified two proteins that allow plants to respond to changes in surrounding light conditions and thereby make photosynthesis more efficient.
www.eurekalert.org
TrxL2/2CP do work in light as well, but are overshadowed by the normal activation machinery in plants and only take center stage in the absence of light. Interestingly, this cascade does not seem to affect photosynthesis itself, as mutant plants without 2CP behave normally in light; however, the 'switching off' mechanism is significantly less efficient in these mutant plants than in wild-type plants. Moreover, the fact that this process is less efficient, rather than absent altogether, suggests that other, as yet unknown, proteins serve similar functions in plants. These researchers thus shed light on how plants reserve the activity of photosynthetic proteins for when it's actually useful.
Click to expand...


Respiration occurs 24/7..
 
oreo57 said:
No, it doesn't work like that.. Below the light compensation point respiration exceeds photosynthesis.
It is not the point of no photosynthesis.
Anyways the wonderful "complication"
www.eurekalert.org

How do plants rest photosynthetic activity at night?

Scientists at Tokyo Institute of Technology have identified two proteins that allow plants to respond to changes in surrounding light conditions and thereby make photosynthesis more efficient.
www.eurekalert.org



Respiration occurs 24/7..
Click to expand...
No net photosynthesis is technically the same as no photosynthesis, no sugar accumulation, and no net oxygen production. The OP thread asked when is the best photo period for optimal photosynthesis. If ambient light starts the circadian clock, then any night time photo period is a waste. This is not supported in practice as majority aquarists turn on light in the evening to view tanks, and their plants should be stunt. I think Dennis Wong said that the first 4 hours of photo period is most productive for photosynthesis, which disminishes gradually thereafter, and any additional lighting beyond 12 hour is a waste. So he recommends that CO2 should be front loaded couple hours before light on. I can’t find his exact citation, perhaps someone can help.
 
tiger15 said:
I think Dennis Wong said that the first 4 hours of photo period is most productive for photosynthesis, which disminishes gradually thereafter, and any additional lighting beyond 12 hour is a waste. So he recommends that CO2 should be front loaded couple hours before light on. I can’t find his exact citation, perhaps someone can help.
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It's commented, among others, in Wetzel's Limnology. It is suggested that it has something to do with photorespiration which increases with O2 concentration near photosynthesizing cells.
In natural waters and in low-tech tanks another factor is even more important: a decrease in CO2 concentration. CO2 is often depleted around noon in natural waters. I think the same happens in low-tech tanks, so plants quit photosynthesis even if lights are still on. That's in line with my observation.
So it seems that CO2 injection makes all the difference.
 
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>>>Photorespiration
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(also known as the oxidative photosynthetic carbon cycle or C2 cycle) refers to a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some of the energy produced by photosynthesis. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle. This process lowers the efficiency of photosynthesis, potentially lowering photosynthetic output by 25% in C3 plants.[1]<<<
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Mysteries..
www.ncbi.nlm.nih.gov

A short history of RubisCO: The rise and fall (?) of Nature’s predominant CO2 fixing enzyme

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) is arguably one of the most abundant proteins in the biosphere and a key enzyme in the global carbon cycle. Although RubisCO has been intensively studied, its evolutionary origins and rise as Nature’s ...
www.ncbi.nlm.nih.gov www.ncbi.nlm.nih.gov
 
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_Maq_ said:
It's commented, among others, in Wetzel's Limnology. It is suggested that it has something to do with photorespiration which increases with O2 concentration near photosynthesizing cells.
In natural waters and in low-tech tanks another factor is even more important: a decrease in CO2 concentration. CO2 is often depleted around noon in natural waters. I think the same happens in low-tech tanks, so plants quit photosynthesis even if lights are still on. That's in line with my observation.
So it seems that CO2 injection makes all the difference.
Click to expand...
The photosynthetic depletion of CO2 in lakes has been documented in many limnology studies, and cited in Walstad book in support of a siesta period in low tech tanks. I can validate it in my window sill planted bowl where pH fluctuates between 7.2 to 8.8 pre and post sunlight period, and with kH 3, the calculated CO2 fluctuates between 3.6 to 0.1 ppm respectively. Growth is very slow though despite vigorous streaming at peak sunlight due to CO2 limitation. Siesta period is not believed to have any benefit in high tech tank, but I provide it anyway to fit my viewing schedule. I’ve never observed closing of stems after mid day siesta in my high tech tank, only in the morning when light turns on.
 
Again and again, I find it amazing how smart plants are. Regulating diurnal rhythms by sugar production? But of course, that's the end-product, that's the point of it all. Both carbon dioxide and light are irrelevant if the other is missing - there's no point in activating photosynthesizing enzymes. How smart...
 
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