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When we started this project about 20 years ago, plant physiologists looked at this problem of rising CO2 and said, "Well, plants will clearly respond to the CO2 as the CO2 rises." Ecologists on the other hand said, "Well, maybe, but how can that happen because what we believe is that most of the nutrients in ecosystems are tied up. That is, they're not readily available. And moreover we have very great ranges of water availability, precipitation, and we know that plant productivity is determined mostly by precipitation and these nutrients."
And furthermore, some experiments in laboratories showed that if you grow plants for a little while in the presence of normal atmosphere and then give them some high CO2 they respond to the CO2 very quickly by their photosynthesis going up, but then in a very short time, hours to days, the rate of photosynthesis commences to come back down again as though the plants can’t handle all this extra carbon dioxide.
So in the face of these, sort of objections by ecologists, plant physiologists said, "Well then, we need to do experiments in the field to find out if, under natural conditions, plants will respond to rising CO2."
Over the course of this 20-year study, what we have found is; Yes, plants acclimate to the high CO2, but that does not mean that they will not take up extra carbon. They do. In other words the answer is somewhere in between if they acclimate there'll be no additional carbon taken up and if they don't acclimate; there will be a massive amount of carbon. In fact, what we've found is that other factors in the environment (and we think the main one is precipitation) regulate the variation from year to year on the amount of carbon that this ecosystem takes up. In very dry years, much less carbon is taken up than in very wet years. And it also turns out that in wet years the CO2 treatment produces a very much greater uptake of carbon here. So in answer to the question "will the plants acclimate?" Yes they will. But will that inhibit the uptake of carbon? No it won’t. And this finding increases the richness of our understanding of how plants respond to CO2 and how ecosystems are going to respond to the high CO2.