Caliban07
Aquarium Advice Addict
Carbon dioxide (co2) in earths atmosphere is around 400ppm and climbing. Most of our aquarium plants that end up in our tanks are grown in plant farms or factories around the world where they have access to this number or sometimes more if enriched further (hydroponics) so why do we expect our plants to accept a drop on average of around 395ppm carbon dioxide without some form of repercussion?
You would think that because the earths soil contains approximately three times that of the atmospheres carbon resources that plants would naturally take up their carbon requirements from their soil roots however, although this does happen where some plants are concerned the majority of their co2 requirements are taken in through the atmosphere via their leaves by a process called diffusion.
As soon as the plant is submerged in water it's access to co2 plummets dramatically. Why is this?
Co2 diffuses 10,000 times slower in water than in air.
Pure h2o at a temperature of 25 degrees Celsius and an atmospheric pressure of 1 bar will contain approximately 0.5ppm of co2. On average a typical aquarium will contain around 5-6ppm of co2 in doors. This can be increased by a number of means which we will go in to later.
Now we need to understand how plants respond to changes in co2 availability when placed under water.
One thing you may have noticed is how different some plants can look when grown emersed as opposed to submersed. Normally the whole leaf structure can look vastly different. Why do plants alter their leaves when placed underwater? One of the obstacles that plants must overcome is the leaf/water interface know as the prandtl boundary layer and it presents probably the greatest resistance to diffusion. This boundary layer surrounding the leaf is much thinner in submerged plants and the surface area of the leaf is often altered. The thinning of the membrane allows easier diffusion of gases through the leaf. Flow also helps this action. Turbulent flow generated at the leaf boundary layer improves the transfer of water containing co2 in to the leaf surface where it can be absorbed.
These new leaves will also have altered amounts of one of the most abundant enzymes on the planet called rubisco.
It is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose and makes up around 50% of soluble leaf protein. Without it, photosynthesis would not be possible. But RuBisCO is pretty poor at its job. Some enzymes can carry out thousands of chemical reactions each second. However, RuBisCO is slow, being able to fix only 3-10 carbon dioxide molecules each second per molecule of enzyme. The reaction catalyzed by RuBisCO is the primary rate-limiting factor of the Calvin cycle during the day. Nevertheless, under most conditions, and when light is not otherwise limiting photosynthesis, the speed of RuBisCO responds positively to increasing carbon dioxide concentration.
Unfortunately However, approximately 25% of reactions by RuBisCO instead add oxygen creating a product that cannot be used within the Calvin cycle. This process reduces the efficiency of photosynthesis, potentially reducing photosynthetic output by 25%. This process is known as photorespiration. If the co2 availability is low enough such that o2 primarily enters the Calvin cycle the plant will waste away (melt) and die.
Plants in low co2 environments have leaves that contain lots of RuBisCO so that more co2 can be captured and entered in to the Calvin cycle. Plants in high co2 environments do not require as much RuBisCO because their is more co2 available and so greater chance of capturing the co2.
When plants are submerged they will often shed their old leaves for food and grow new leaves reflecting these alterations. This adaptation can take time and often results in algae outbreaks as old leaves are broken down.
Plants that go from low co2 to high co2 adapt much better than those that go from high co2 to low however, once the latter have adapted they can continue to grow healthily. These plants are more likely to be the 'low tech' plants such as Anubias and Crypts. Understanding how the plants adapt to co2 changes is important and highlights the need for patience.
How can we ensure we have enough co2?
In non injected co2 tanks having more fish equals more bioload which equals more food which equals more waste which equals more microorganisms with ultimately equals more co2 via respiration. Having a generously stocked tank can increase co2 levels.
Some water supplies contain healthy amounts of co2 depending on the source and so frequent water changes can increase co2 availability.
It is important to understand that plants can survive in non injected co2 environments but this is not always the case.
What factors impact my success in planted tanks with regards to co2?
If I am injecting co2 in to the water column I immediately have a better chance at growing a wider variety of aquatic plants but we must look at these points below to determine our chances of success even with additional co2.
Size of aquarium.
Much more difficult to keep co2 in solution long enough for plants to obtain enough as their is more likely to be a larger water space to plant ratio and thus co2 is wasted
Plant mass
More plants will require more co2.
Plants species
Different plants have different co2 requirements. Therefore their uptake rates can differ dramatically. Most stem plants for example are aquatic weeds that take up co2 quickly.
Light intensity
Light intensity drives co2 uptake and so the higher your lighting levels the more likely co2 will become depleted quickly. Therefore a solution in lower co2 environments can be to lower the light intensity and reduce the plants demand for co2.
Flow pattern/strength
As discussed above flow cannot be underestimated. Do you have enough and is it distributed correctly?
Temperature
Higher temps will hold less co2.
Surfaces agitation.
This will drive co2 out of the water in most cases. Focus on flow and Lower your outlet to a gentle ripple. Healthy plants produce good amounts of o2.
Please do not ignore co2.
It moves slowly in water and the plants have a hard time obtaining it even in injected tanks. If you are successful without supplementing co2 then congratulations you have found a balance with regards to the above factors that is not easy to achieve in most cases but this does not always work.
If your plants are struggling please rule out co2 deficiency before anything else as there is more than enough evidence out there to suggest that co2 is the major limiting factor when it comes to growing aquatic plants.
Hope this helps and thanks for taking the time to read.
Cal.
You would think that because the earths soil contains approximately three times that of the atmospheres carbon resources that plants would naturally take up their carbon requirements from their soil roots however, although this does happen where some plants are concerned the majority of their co2 requirements are taken in through the atmosphere via their leaves by a process called diffusion.
As soon as the plant is submerged in water it's access to co2 plummets dramatically. Why is this?
Co2 diffuses 10,000 times slower in water than in air.
Pure h2o at a temperature of 25 degrees Celsius and an atmospheric pressure of 1 bar will contain approximately 0.5ppm of co2. On average a typical aquarium will contain around 5-6ppm of co2 in doors. This can be increased by a number of means which we will go in to later.
Now we need to understand how plants respond to changes in co2 availability when placed under water.
One thing you may have noticed is how different some plants can look when grown emersed as opposed to submersed. Normally the whole leaf structure can look vastly different. Why do plants alter their leaves when placed underwater? One of the obstacles that plants must overcome is the leaf/water interface know as the prandtl boundary layer and it presents probably the greatest resistance to diffusion. This boundary layer surrounding the leaf is much thinner in submerged plants and the surface area of the leaf is often altered. The thinning of the membrane allows easier diffusion of gases through the leaf. Flow also helps this action. Turbulent flow generated at the leaf boundary layer improves the transfer of water containing co2 in to the leaf surface where it can be absorbed.
These new leaves will also have altered amounts of one of the most abundant enzymes on the planet called rubisco.
It is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose and makes up around 50% of soluble leaf protein. Without it, photosynthesis would not be possible. But RuBisCO is pretty poor at its job. Some enzymes can carry out thousands of chemical reactions each second. However, RuBisCO is slow, being able to fix only 3-10 carbon dioxide molecules each second per molecule of enzyme. The reaction catalyzed by RuBisCO is the primary rate-limiting factor of the Calvin cycle during the day. Nevertheless, under most conditions, and when light is not otherwise limiting photosynthesis, the speed of RuBisCO responds positively to increasing carbon dioxide concentration.
Unfortunately However, approximately 25% of reactions by RuBisCO instead add oxygen creating a product that cannot be used within the Calvin cycle. This process reduces the efficiency of photosynthesis, potentially reducing photosynthetic output by 25%. This process is known as photorespiration. If the co2 availability is low enough such that o2 primarily enters the Calvin cycle the plant will waste away (melt) and die.
Plants in low co2 environments have leaves that contain lots of RuBisCO so that more co2 can be captured and entered in to the Calvin cycle. Plants in high co2 environments do not require as much RuBisCO because their is more co2 available and so greater chance of capturing the co2.
When plants are submerged they will often shed their old leaves for food and grow new leaves reflecting these alterations. This adaptation can take time and often results in algae outbreaks as old leaves are broken down.
Plants that go from low co2 to high co2 adapt much better than those that go from high co2 to low however, once the latter have adapted they can continue to grow healthily. These plants are more likely to be the 'low tech' plants such as Anubias and Crypts. Understanding how the plants adapt to co2 changes is important and highlights the need for patience.
How can we ensure we have enough co2?
In non injected co2 tanks having more fish equals more bioload which equals more food which equals more waste which equals more microorganisms with ultimately equals more co2 via respiration. Having a generously stocked tank can increase co2 levels.
Some water supplies contain healthy amounts of co2 depending on the source and so frequent water changes can increase co2 availability.
It is important to understand that plants can survive in non injected co2 environments but this is not always the case.
What factors impact my success in planted tanks with regards to co2?
If I am injecting co2 in to the water column I immediately have a better chance at growing a wider variety of aquatic plants but we must look at these points below to determine our chances of success even with additional co2.
Size of aquarium.
Much more difficult to keep co2 in solution long enough for plants to obtain enough as their is more likely to be a larger water space to plant ratio and thus co2 is wasted
Plant mass
More plants will require more co2.
Plants species
Different plants have different co2 requirements. Therefore their uptake rates can differ dramatically. Most stem plants for example are aquatic weeds that take up co2 quickly.
Light intensity
Light intensity drives co2 uptake and so the higher your lighting levels the more likely co2 will become depleted quickly. Therefore a solution in lower co2 environments can be to lower the light intensity and reduce the plants demand for co2.
Flow pattern/strength
As discussed above flow cannot be underestimated. Do you have enough and is it distributed correctly?
Temperature
Higher temps will hold less co2.
Surfaces agitation.
This will drive co2 out of the water in most cases. Focus on flow and Lower your outlet to a gentle ripple. Healthy plants produce good amounts of o2.
Please do not ignore co2.
It moves slowly in water and the plants have a hard time obtaining it even in injected tanks. If you are successful without supplementing co2 then congratulations you have found a balance with regards to the above factors that is not easy to achieve in most cases but this does not always work.
If your plants are struggling please rule out co2 deficiency before anything else as there is more than enough evidence out there to suggest that co2 is the major limiting factor when it comes to growing aquatic plants.
Hope this helps and thanks for taking the time to read.
Cal.