Plants breathe. Although this sounds strange, they do:
A little summary on the plant life cycle, especially the photosynthesis:
The plant uses the energy from the light to assimilate it’s own sugars to create all it’s structures (like stems, flowers and … resin!). In a complicated reaction in which H2O (water) and CO2 (carbon dioxide) are combined, under the influence of light, it creates these sugars by the combination. When plants get enough light and their nutrients are abundant too, other factors get limiting… With only 0,03% CO2 in the air this gas becomes quite a limiting factor in the growing process of the plant!
In nature the same thing happens, but there the plant can also absorb CO2 from its soil! Sounds bizarre? Well… maybe this seems bizarre, but when we look at natural soils we find higher concentrations of CO2, even up to 1-2%!!! Many plants have mechanisms to absorb and transport CO2 from the roots to the shoot (and leaves), thus resolving the problem of CO2-shortage near the leaves!
“How come we don’t find any literature on CO2-uptake by the roots???”
In the last few decades specialized CO2-devices have been developed to augment the CO2-concentration for the above-ground parts of the plants. General consensus was that plants take up CO2 most effectively with their leaves. It is true that in their leaves there are specialized structures (stomata), which regulate the gas-exchange of the plant. When the CO2-concentration augments near these stomata the plant has to do ‘less effort’ in getting the CO2 inside the plant. This results in, for example, an augmentation of biomass, due to ‘more photosynthesis’. Other effect, that can be seen, is that the plant loses less water because the stomata can be more closed, this is why the plant can stand higher temperatures when it receives enough CO2!
In the beginning of CO2-nutrition, it was thought to be impossible to augment the CO2-concentration aboveground because greenhouses were less ‘closed’ and less regulated, but also because lot of crops were grown outside. This was the main reason to investigate the effects of CO2-nutrition near the roots in those days. Most articles regarding this subject date from 1920 to the late 1970’s. After this period CO2-nutrition aboveground gained popularity, because the yield-gains were much higher!
“Now, what can these ‘old’ articles learn us?”
Most important findings were that:
A. the effects of 12-hours CO2 treatment after 3 weeks
B. after 6 weeks
Control-plants on the left, CO2 treated plants on the right
“The response of plants to high concentrations of CO2 depends on the species. Potato plants, for example are particularly well suited to CO2 enrichment of the root zone.” [4]
“It has been shown that the amount of CO2 absorbed by the roots was as much as 25 % of that taken up from the atmosphere by the leaves. Translocation only takes place during the light period and parallels the increase in transpiration rates. [4]
In potatoes treated with high concentrations in the soil 18% of the incorporated CO2 has been shown to be taken up by the roots.” [2,3]
”The introduction of soluble carbonates introduced into the soil together with fertilizers increased the yield of several crops by up to 18%.
Addition of 30 or 50 kg of CO2 per hectare, supplied as ammonium carbonate, increased the yield of sugar beets 7 and 16% in two trials.” [2, 6]
“Even at normal concentrations of CO2 (0,028%) small amounts of carbon were derived from CO2, taken up by the roots of Xanthium plants.” [3]
“In an experiment in which potatoes were treated with CO2 for 12 hours and the effects were evaluated at 2, 4 and 6 days, there was a progressive increase in the total plant dry weight from 2 to 6 days. The concentration of several organic acids (malic and citric acid) increased in proportion to the increase in total dry weight, indicating an increase in carbon fixation by CO2-treated plants.
Treatment with CO2 even has its effect for such a short period of time.” [4]
“It has been demonstrated that HCO3- was taken up by the roots. The identified products of fixation are malic, citric, aspartic and glutamic acids, serine, aspargine, glutamine, and tyrosine.” [2]
“The fixation of CO2 by plant root takes place through phosphoenolpyruvate carboxylase.” [5]
“The uptake of C14O2 by the roots of intact bean seedlings has been shown in an experiment with 18 hours of exposure in the light. Most of the radioactivity was in the stems, indicating that the fixation products were translocated upwards.” [2]
“With low pH (4-5) higher CO2-concentration in solution give growth-reduction of roots.” [1]
“The necessity of aeration arises only because of the inadequate rate of transfer of gases by diffusion.” [1]
Literature:
[1] Erickson, J. 1948. Growth of tomato roots as influenced by oxygen in the nutrient solution. American journal of botany. Volume 33; 551-561
[2] Stolwijk, J.A.J.; Thimann, K. V. 1957. On the uptake of Carbon dioxide and bicarbonate by roots, and its influence on growth. Plant physiology. Volume 32; 513-520
[3] Skok, J.; Chorney, W.; Broecker, W. Dec 1962. Uptake of CO2 by roots of Xanthium plants. Botanical Gazette. 118-120
[4] Arteca, R.N.; Poovalah, B.W.; Smith, O.E.1979. Changes in carbon fixation, tuberization, and growth induced by CO2 applications to the root zone of potato plants. Science. Volume 205; 1279-1280
[5] Jackson, W. A.; Coleman, N. T. 1959. Fixation of carbon dioxide by plant roots through phosphoenolpyruvate carboxylase. Plant and soil XI, no1; 1-16
[6] Grinfeld, E. G. 1954. On the nutrition of plants with carbon dioxide through the roots. Doklady Akademii Nauk SSSR. Physiology of plants. Volume 97, No 5; 919-922
