CO2 and plants

I am interested in the opinion of professionals, including climatologists. I was happy to read the article by Irina Delusina. As a researcher, I work with plants, study the work of genes that are in chloroplasts. In those that carry out photosynthesis, “besiege CO2” in terms of planetologists. Inevitably, I look into the conjugated areas of Plant Science, I read about what and how are the proteins that encode these genes. Therefore, I was surprised by the assertion that “the excessive content of CO2 ... removes the system from balance ... ultimately this leads to extinction ... the disappearance of plant species and animals ... The reasons include barbaric treatment of nature, and, as one of its aspects, pollution of the atmosphere with carbon dioxide.” In the text of Irina Dlusina there is no direct statement that an increase in the concentration of CO2 is toxic for plants. However, if the reader has long forgotten (or did not listen to) the university course of plant physiology, then by reading this text this impression can be created. Therefore, let's recall how the plants, photosynthesis and CO2 are connected.

At school, we are taught that plants use sunlight energy to synthesize glucose from CO2 and water. At the university, it is added that sunlight launches one phase (the so -called light), and the synthesis of glucose from CO2 and water occurs in another phase (the so -called dark). And these are really different phases: one process proceeds in membranes, and the other in the cellular matrix, in the water phase. Chloroplast genes mainly encode the proteins of the light phase of photosynthesis, they do not have a direct attitude to reactions with CO2, so we will not talk about them further. In chloroplasts of flowering plants, only one gene (RBCL) encodes an enzyme that participates in the dark phase, in CO2 fixation, in the Calvin cycle. But this is the most important enzyme - ribulosobisphere carboxylase/ oxygenase (RBFK/ O, or Rubisco). It is he who attaches CO2 to the organic molecule (ribulozo-1,5-bisphosphate) and launches the entire Calvin cycle. This enzyme (Rubisisco, Rubisco) works extremely slowly, limits the work of the entire CO2 fixation system, the plants are forced to develop it in huge amounts. Why is it so?

Photosynthesis occurred more than a billion years ago, when the concentration of CO2 in the air was much more than now. Carbon dioxide penetrated the cells easier, dissolved into them, partly turning into NSO3–. There were much more CO2 and NSO3 - in the cells. But then photosynthetic organisms literally pumped out CO2 from the atmosphere, besieged it, as planetologists say. At the same time, some islands created from CO2. But the problem arose: Rubisco works well with a much higher CO2 content than it turns out now when it is passive in the cage. In the process of evolution, photosynthetic organisms learned to increase the concentration of CO2 in the place where Rubisisco “works” in the cytosole of cyanobacteria or in a stroma of chloroplasts in algae and plants. Different mechanisms were involved: Karboangidrase enzymes accelerate the transformation CO2 + H2O ↔ NSO3– + H +; In plants, there are several varieties of C4-cycle, in which HSO3– (with a lower concentration in the cage) joins another organic molecule (phosphonelpiruvat), it is directed to the place of work of Rubisco and there is split there with the formation of CO2. A special type - CO2 Concentrationing Mechanism, CCM - occurred in cyanobacteria. Without trying to understand these mechanisms, we remember: with the fall of CO2 content in the air, plants, algae, cyanobacteria had to produce and apply complex, energy -consuming mechanisms to adapt to a new reality. And to synthesize Rubisco in huge quantities - in plant leaves it is the most massive protein.

In the quotes given by the author, the first one from the text of Yulia Latynina - “the more CO2 will be in the air, the greener and juicier our planet will be” - really causes a smile. Photosynthesis is a very effective process, and CO2 intracellular concentration mechanisms work reliably. Plant growth - so that the planet becomes greener - limits not photosynthesis, but completely different factors, including the economic activity of mankind. But the phrase “no from him, CO2, harm, okre good” looks very believable. In any case, if we limit ourselves to the influence of this gas on one (any) type of plant. As an enhanced absorption CO2 affects competition between different species of plants, whether this can lead to the crowding out of some species, to the fall of species diversity - I do not understand this. And I will get acquainted with interest with examples if they are shown to me. I heard about such examples in the field of mineral (nitrogen) nutrition, but in relation to CO2 it seems amazing to me so far.

Therefore, I will ask a question. The article by Irina Dlusina contains a clear hint that an increase in CO2 content in the air will be harmful (toxic?) For plants. I ask you to explain how and in what it will be expressed. Of course, as a result of an increase in the CO2 content in the air, temperature may increase, the climate may change, and this can already harm plants. As a researcher, I just study the effect of fever on chloroplasts. But these are different questions, and let's not mix them.

Evgeny Lysenko,
cand. Biol. sciences, Art. scientific. sore.
Institute of Physiology of Plants
them. K. A. Timiryazeva RAS

PS I am not a specialist in the dark stage of photosynthesis (Calvin cycle and other processes associated with CO2 fixation). However, in the Russian “plant” scientific community there are few good researchers of the photosynthesis light phase and there are practically no one left for the dark phase. Not fashionable. Therefore, I allowed myself to state my understanding of this situation and ask a question.