The influence of CO2 on acorns
Plants grow better if they receive more CO2, aren’t they? In first instance this appears to be the case. Plants get bigger and are also producing more and bigger seeds. But if that is good news for everyone, that is something that remains to be seen.
Who is looking further than appearances sees that more happens than only growing bigger. Seeds and fruits from annual plants, like lots of our crops, who grow with extra CO2 contain less minerals. They also contained less proteins. And that is a problem, because we and other eaters de need those minerals and proteins.
There are lots of questions related to how and why the amount of protein and minerals in seeds and fruits is lower when there is more CO2 available. Is it because the plants are not taking up enough minerals compared to the amount of CO2 they transform into sugars? Or is it because the metabolism of the plant changes when there are more sugars available? All questions that are waiting for an answer.
Bigger acorns
A new study tries to answer then, but also on the question how extra CO2 influences perennial plants like trees. The study published as “Elevated atmospheric CO2-induced reprogramming leads to decreased seed protein and nutritional quality in forest trees” looks specifically at the composition of acorns.
For the study 180 year old oaks grew for 8 years in an environment with an increased CO2 concentration. During these times the acorns of the oaks produced were bigger than those of also 180 year oaks that were growing with ambient CO2 concentrations.
During the last two years the researchers collected the acorns for further study. While doing this they paid attention to that the acorns they collected form both groups of trees were of the same size. The first thing the researchers did was checking if there was a difference in germination rate. This appeared not to be the case under the tested condition.
Subsequently the researchers studied the contents of the acorns. The amount of minerals they contained, the amount of protein, and which proteins were present. Also, which other metabolites were present and which genes were active was studied.
Less nutritious
For the minerals present the researchers did not see any difference. But they did notice that in acorns that grew on trees grown under elevated CO2 levels there were more metabolites present that bind minerals. The consequence of this is that some minerals were present but less available for use by those who eat the acorns. The acorns of trees that grew under elevated CO2 levels also had less proteins.
While studying the proteins and genes that are active in the acorns two things got the researchers attention. The first is that in acorns from trees grown under elevated CO2 levels there were less proteins and genes active that are involved in the production of amino acids. Secondly, it appears that those oaks make more sugars and specialised metabolites.
A higher CO2 concentration is thus not only results in that trees grow better, they also reorganize their metabolism. This has as a consequence that they put more energy into the storage of sugars and their defence. The cost of this is the nutritional value of the acorns. The acorns themselves although, appear not to be negatively impacted, they still germinate without problems.
Literature
Barbara Karpinska, Rosa Sanchez-Lucas, Andrew Plackett, A Rob MacKenzie, Christine Helen Foyer, Elevated atmospheric CO2-induced reprogramming leads to decreased seed protein and nutritional quality in forest trees, Plant Physiology, 2025;, kiaf463, https://doi.org/10.1093/plphys/kiaf463
Plant en Zo 