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Plants and CO2 levels through the ages  RSS feed

 
pollinator
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If you look at a graph of world CO2 levels and temperature from the Cambrian era to the present, you see little to no correlation between the two.  But there a strong trend downwards in CO2 levels starting from 7000ppm in the Cambrian and dropping down to 180ppm during the Quaternary glaciation, the most recent downward excursion being 20,000 years ago.  This drop in CO2 levels is to be expected since plants are busy pulling CO2 out of the air with the resultant fixed carbon being deposited into the ground and on the sea floor.  A portion of this sea floor carbon gets subducted deep into the earth's interior via plate tectonics, becoming forever lost to the biosphere except for what little bits of it get released via volcanoes and mid-ocean hydrothermal vents.   So the general long term trend is for atmospheric CO2 levels to drop as carbon gets pulled out of the air and put into the ground.  

Angiosperms first appeared during the Cretaceous when CO2 levels were in the 1700 to 1800ppm range and have had to adapt  to steadily dropping CO2 levels from that time forward. C3 photosynthesis is the original chemical pathway that evolved in algae during the Precambrian era  and is found in all sea plants and most land plants. But 7 million years ago some groups of monocots and dicots evolved C4 photosynthesis in response to the extremely low CO2 levels they were experiencing during the Quaternary period.  A drawback of C4 is that it works best at hot tropical temperatures, limiting its use in the cooler parts of the globe, so 85% of the world's plants are still C3.

If you look at a curve of plant growth rate vs. CO2 levels, it rises sharply with increasing CO2 levels until CO2 levels reach 1200ppm where the growth rate starts to level off.  This increased growth rate at higher than current atmospheric CO2 levels has long been known to commercial greenhouse growers, many of whom use CO2 generators to maintain a CO2 level in the greenhouse of between 1000 and 1500ppm.  At these higher CO2 levels, plants grow faster, have higher yields, produce larger, thicker leaves, larger flowers, require less water, and are more resistant to environmental stresses.   Leaves grown at these higher CO2 levels produce fewer stomata and have to open them less to obtain the required CO2, increasing their drought tolerance.

Photorespiration, an inefficiency in the photosynthetic process where the enzyme RuBisCO reacts with 02 rather than the desired CO2, disappears at 1200ppm, but gets worse and worse as CO2 levels drop below that point, and is apparently as artifact of low CO2 levels.  C4 photosynthesis minimizes losses due to photorespiration.

At the other end of the scale, growth and seed production in C3 plants drops off rapidly at lower than current CO2 levels.  An Arabidopsis growing at 180ppm, the lowest CO2 levels experienced during the last ice age, had only 8% of the growth rate of the same plant growing at current CO2 levels.  Below 150ppm, C3 plants essentially stop growing, so the 180ppm lows during the Quaternary glaciation came within spitting distance of killing off many C3 plants.  

CO2 levels were 180ppm st the peak of the ice age, slowly rose to 270ppm as we came out of the ice age, then continued rising as human activity added CO2 to the atmosphere and is over 400ppm now.  This boost in CO2 levels has goosed plant growth rates and is part of the oomph behind the increase in crop yields helping to feed the growing human populations.  Satellite images are showing an 11% increase in foliage cover in arid regions around the world from 1982 to 2010.  The spread in the  seasonal cycle in CO2 levels monitored at Moana Kea observatory increased from 14ppm in 1975 to 17ppm in 2013 as worldwide plant photosynthetic activity is ramping up with rising CO2 levels.

So it looks like plants are best adapted to growing in the mid-1000's ppm CO2 atmosphere they originally evolved in, are showing reduced growth rates/seed production and displaying metabolic derangements like photorespiration in our modern CO2 impoverished atmosphere.  So while some humans might be concerned about rising CO2 levels, the plants are saying "bring it on, we're half starved out here".
Staff note (Daron Williams):

Hello all, I'm afraid this topic is more appropriate in the cider press. Those of you with enough apples are free to create a post there to discuss this subject. This thread is now locked.

 
gardener
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How curious, I don't see any mention of the fact that during photosynthesis plants take in O2 and respire CO2, it is during the night time cycle of photosynthesis that plants take in CO2 and respire O2.
There is also no mention that in the Cambrian era there was far more oxygen in the atmosphere than today which led to giant insects and some animals.

I'm also not certain of what this dissertation means to accomplish since it is merely a CO2 slanted listing of known data.
So I have to ask, Mike, what is your point?
Sure this is interesting data but to what purpose are you posting it?

Is it only to point to supposed prime CO2 conditions?
CO2 conditions need to have the O2 levels listed, is it not expected that if CO2 levels are at say 180ppm that O2 levels would not also be in that ball park range?
Since the cycle is (starting at sun above the horizon) O2 in and CO2 out followed at dusk with CO2 in and O2 out, we can expect the gas level around the test plants to be in a state of equilibrium in a 24 hour period.
If carbon is being put into the soil by plants, what happens when the microorganisms process said carbon and respire to the atmosphere?
Volcanoes expel a lot of gasses, including CO2 but they also expel several other gasses of which carbon is one of the atoms in their molecular structure, but these aren't addressed either.

I like the post, but it is very much not completing a picture.
 
Mike Turner
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With C3 and C4 photosynthesis, plants absorb CO2 and release O2 when they are exposed to light.  There is the side reaction of photorespiration in C3 plants where plants absorb O2 and release CO2 that occurs when CO2 levels are low.  

The only plants that absorb CO2 and release O2  at night are plants with crassulacian acid metabolism (CAM), C3 and C4 plants do this during the day.  

The terms "light reaction" and "dark reaction" in photosynthesis can sometimes be confusing , thinking that light reactions occur during the day and dark reactions occur at night. Light reactions can occur whenever the plant is in light.  Dark reactions don't require light to occur, all they require are the chemical products produced by the light reactions and, for most plants, occur alongside the light reactions when the plant is exposed to light.

O2 levels were below present day levels during the Cambrian era.  The first O2 peak didn't occur until the Carboniferous era and a second lower peak occurred toward the end of the Cretacious.  

Neither insects or land animals existed during the Cambrian era, insects first appeared during the Ordovician era, and the first land animals appeared during the Silurian era.

There has been no correlation between CO2 and O2 levels through the ages as there are factors in addition to plant and animal activity that effect their levels.  CO2 is added by volcanic activity, especially the super eruptions that formed the Deccan and Siberian traps.  CO2 is removed by newly exposed rock when new mountain ranges are formed.  O2 is also removed by oxidation of newly exposed rock during mountain building sessions.

Not all of the carbon put into the soil by plants is respired by soil organisms, especially when deposited into anaerobic conditions.  Coal and oil deposits are the result of this.
 
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I have heard that plants grow better in high CO2 environments... but apparently not well enough to fully make use of the increased levels.  In other words, increased plant growth from a rise in CO2 does not fully remove the excess amounts of that gas (if they did, CO2 levels would not have doubled since the last Ice Age).  Unless I'm missing something...
 
Bryant RedHawk
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good to know those facts, thank you Mike, Those aren't  my area and it doesn't surprise me to discover I was out of the proper timeline.

But still I am wondering what this means for us today, right now, how is this relevant to the current global warming event, melting ice caps and glaciers?
Or is it just giving us a history lesson? (which I am great with, because I love learning things all the time)
 
gardener
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One thing to keep in mind is that you can't just throw more CO2 into the mix and expect plants to grow better. They need nutrients, water, a stable climate, etc. to really thrive. This image defines it fairly well:



Unless you address the limiting factor you can add all you want of the other factors and get no real benefit. This is why in field studies plants don't seem to be responding to increases in CO2. The research I have read on this do not find that C02 is the limiting factor for plant growth. In a greenhouse where you can have complete control of all the factors then increasing C02 can increase plant growth. But these results do not seem to translate to the field.

In my own experience as a restoration ecologist running restoration projects where I have planted tens of thousands of trees/shrubs the lack of water due to drought seems to be the biggest limiting factor to plant growth. When I improve that my plants do much better and grow much bigger. But the droughts of the last few years have been a huge limiting factor for my projects.
 
Mike Turner
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If you look at the earth's history since the Cambrian, compared to prehistoric norms, our current time has unusually low temperatures and CO2 levels.  The only time that came close was the latter half of the Carboniferous through the first part of the Permian era.  Through most of their evolution, plants were living in a world with ice-free polar regions and a CO2 level 3 to 4 times higher than the current levels and those are the  CO2 levels that .they are best adapted for.  The fall line along the east coast of North America is where the sea shore was located for the majority of the time since the Atlantic ocean was formed and it left its mark on the topography.  

There was an entire plant community, the polar deciduous forest, that existed above the arctic circle in North America until the poles started freezing up about 8 million years ago.  This plant community was populated with the tree species that are now found in the temperature zone.
 
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I am aware of this dynamic. Since 2015 i have watched my plants grow steadily larger, torn between congratulating myself on increasing levels of humus in the soil and worry over the C02 factor. It is also a bit early according to predictions, 400 ppm is not supposed to be sufficient for an observable difference. On the other hand if Africa's temperatures are rising at twice the global average I suppose it is not impossible that CO2 levels are as well, though I have no idea of the science behind this.

As a plantswoman I can't say I wholeheartedly approve. Plants grow big and floppy and keel over in the wind. And more tasty to pests.  The amount of biomass is increasing so much that I wear myself this time of year chopping  and composting, plus most of the rest of the year I am goat trying to keep plants away from each other. So much so that I have ceased to haul in manure except for a tiny bit for potting.

I too wonder if CO2 on its own is sufficient to account for the increased growth, and can only suspect that this would depend on what is in it. Ancient carbon should be great but then again they make glyphosate and Agent Orange from it so who knows?

Related to this concern is whether the faster growing plants are able to make high density nutrient rich food to sustain healthy humans? I mean, even if we grant that the effect is real that does not necessarily mean it is to our advantage. Pardon my flakiness about the eons but I seem to recall that the dinosaurs went extinct during an era of high carbon levels? All I can say is that greenhouse tomatoes are terrible compared to organic sunkissed ones and taste in a healthy mouth should be an indicator of nutrients.

Water is my limiting factor too.  Even on my tiny 2.5 acres I am not able to grow about 1/3 of it because I do not have sufficient water. Bit by bit as older parts start to become self sustaining I move driplines, but it literally is a calculation every spring how much I can afford to grow. I am more and more starting to think of the landscape as a waterholding flow mechanism, and am converting my dam to a wetland. We are next to the sea so with rising temperatures more evaporation is making the drop in rainfall easier to deal with. However I am also preparing for floods this winter just in case because all that extra humidity looks like it is going to come down as soon as the weather cools. For both purposes looking at water in the air, plants, and humus seems to make more sense than open water which I am coming to detest. It evaporates faster. in the dam too

It gets easier as the ecosystem matures. Shade trees especially if nitrogenous work wonders, as do swales. I am most fortunately on a foothill at the bottom of mountains, so slowing down water flow with a few escape systems in case of floods is working just fine. I am working outwards from zone 1 and getting there one guild at a time.
 
pollinator
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Natasha, those are important observations. I'm noticing that they are being tested in a lot of research these days. Apparently, with many food plants, elevated CO2 levels promote vegetative growth at the expense of some reproductive factors, such as grain plants forming kernels with lower levels of proteins and oils but bulked up with carbohydrates.

Then there is the matter of "weeds" in a CO2-rich environment...if we already have to manage our food crops in the face of competition, this only makes our job harder.
 
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Even if this were true, I don’t think this makes for any kind of positive argument that increases CO2 levels might be in some way “good”.

If some plants adapt/are adapted to make more use of elevated CO2 levels then we are looking at disruptions of natural eco-systems on a global scale. Plants with even a small edge on photosynthesis are in an arms race with their neighbours. If increased CO2 means they grow faster, larger, fruit earlier and set more seed then we are facing massive disruption to the existing balances.

It may be good for some plant species, but it is hard to argue that it is better for the wider ecosystems, or indeed for people who depend on them.

For context, you might like in visualise the encroachment of kudzu on a suitable area... but drastically increase the areas it can grow prolifically in.
Staff note (Daron Williams):

Hello all, I'm afraid this topic is more appropriate in the cider press. Those of you with enough apples are free to create a post there to discuss this subject. This thread is now locked.

 
I've got no option but to sell you all for scientific experiments. Or a tiny ad:
3 Plant Types You Need to Know: Perennial, Biennial, and Annual
https://permies.com/t/96847/Pros-cons-perennial-biennial-annual
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