Nothing happens for some plant types, and even the authors of this study said may. They had good reason to.
To quote from its abstract:
The consensus of many studies of the effects of elevated CO2 on plants is that the CO2 fertilization effect is real (see Kimball, 1983; Acock and Allen, 1985; Cure and Acock, 1986; Allen, 1990; Rozema et al., 1993; Allen, 1994; Allen and Amthor, 1995). However, the CO2 fertilization effect may not be manifested under conditions where some other growth factor is severely limiting, such as low temperature (Long, 1991). Also, plants grown in some conditions, where limitations of rooting volume (Arp, 1991), light, or other factors restrict growth, have not shown a sustained response to elevated CO2 (Kramer, 1981).
Note well that again they use the term may. This is because -- unlike you -- they seem to recognize that even though the effect is real and will have an impact in many locations and conditions, including those that generally hold in agriculture where one generally avoids growing plants in strongly resource constrained environments, one can certainly suppress the effect (or fail to observe it in the wild) in specific environments, and they go even further and note that the effect is differential according to plant type with some plant types more likely to exhibit a stronger response or be resource limited than others.
The bulk of this report simply works through specific food crop species and estimates their likely response to a mix of increased CO2 and the imagined climate changes that are predicted, or projected, or prophecied (as you wish) by the GCMs that so far haven't done a very good job of PP or P-ing the climate.
You would obviously like more papers:
(Abstract: Satellite observations reveal a greening of the globe over recent decades. The role in this greening of the “CO2 fertilization” effect—the enhancement of photosynthesis due to rising CO2 levels—is yet to be established. The direct CO2 effect on vegetation should be most clearly expressed in warm, arid environments where water is the dominant limit to vegetation growth. Using gas exchange theory, we predict that the 14% increase in atmospheric CO2 (1982–2010) led to a 5 to 10% increase in green foliage cover in warm, arid environments. Satellite observations, analyzed to remove the effect of variations in precipitation, show that cover across these environments has increased by 11%. Our results confirm that the anticipated CO2 fertilization effect is occurring alongside ongoing anthropogenic perturbations to the carbon cycle and that the fertilization effect is now a significant land surface process.)
Probably the best review article on the effect on trees, in particular, is this:
where in laboratory experiments on trees increasing CO2 by 300 ppm increased growth by 50 to 60%. Idso remarks that the problem with laboratory experiments is the opposite of what you assert -- it is difficult to grow trees in the lab without constraining their roots and access to resources and work he cites (in less abundance as it was ongoing in 1993) suggested that the response in the wild is even higher.
In general, in the mean, increasing ONLY CO2 in the environments of most wild plants does, in fact, increase their biomass and the net biomass of the Earth has almost certainly substantially increased on average, allowing for changes in land use over the last century. The effect is pronounced and relatively enormous in trees (and yes, I can cite papers there too -- a recent study at Exeter found a strong increase in tree growth rates across all of Europe due to increased CO2 fertilization). If you want to address crop species, you really need to look at crop yields where the plants are fertilized and irrigated as needed or grown in environments with consistently adequate rainfall as is the practice over a rather substantial majority of the world's agricultural production. There the benefits are clear, consistent, and large in the lab, and there is little good reason to doubt an average positive response in the field even though measuring the response with all of the confounding factors is difficult. Even without fertilization and irrigation, since nitrogen fixing species themselves respond positively to CO2 and since one response to CO2 is improved respiration efficiency and water retention, one usually gets some positive response, but in drought constrained, fertilized environments one can sometimes see no or even negative responses because CO2 aside it is a bad idea to overfertilize or outgrow your water supply.
Now that we've established that the literature on this -- which you clearly have not read outside of a single google search or the moral equivalent thereof -- is widespread and not limited to a single Nature article on wild grasses (which are one of the least likely species to benefit from increased CO2 because grasslands are often grasslands because they are resource constrained) let's address the effectiveness of your debate style. Do you really think ad hominem improves your argument? I have at no time asserted that I am the "smartest motherfucker in the room", and calling somebody "Mr. Smarty-pants" is the act of a child in a child's argument, not an adult. Asking for references is perfectly reasonable, although they aren't terribly difficult to find on your own, but seriously, slashdot is already way too much like kindergarten as a debate forum to make it even worse. I would respectfully suggest that you respectfully reply, even to individuals that you think are wrong, and that you make an effort not to argue like a five year old.
To conclude, In all of your replies so far, outside of your bellittling language and sarcasm, you have made a single categorical statement -- that CO2 will have and has had no effect on plant growth or crop yield or biomass increase because plant growth is "almost never" CO2 limited that, I trust, I have just proven to be pure bullshit at least as far as the vast majority of the literature on the subject is concerned. Again, this isn't really even a matter worthy of contention -- in C3 plants it increases respiration efficiency and water retention (making better use of even constrained water resources, hence its impact at the boundaries of deserts), it increases photosynthesis rates and efficiency, it increase the rates of nitrogen fixation in nitrogen fixing species (again directly feeding back into a potentially rate limiting resource). It is standard practice to boost CO2 in greenhouses, the positive effect on the biosphere is clearly visible from satellites, the measured effect is huge in trees and is clearly observed in natural tree populations, and the variability of the effect across C3 species (where it is larger for tuberous plants, for example, than thin-rooted plants) is established. The effect is nearly always positive although of course it is still being studied and can be neutral to negative in certain environments.
In actual agriculture the effect is almost always going to be beneficial and fairly substantial, supporting my claim that it has had a fairly substantial positive impact on global food production as the planet has gone from a CO2-limiting 280 ppm to 400 ppm.
Bear in mind that for most of the geological history of the Earth, CO2 levels have been far higher than they are today, and that during the last glacial period partial pressures dropped to just above the edge that would have caused mass extinction of at least some plant species. Plants in general are well-adapted to use more carbon dioxide than the atmosphere contains right now given "average" levels of water and nitrogen and other natural constraining resources, and this can hardly be a surprise as it makes perfect sense. I realize that this is an inconvenient fact if your only interest is to demonize CO2 and belittle anyone that doesn't agree with you, but as I said in the top comment that you are replying to, opponents of carbon dioxide are happy to count the "death toll" of climate change on the extrapolation of the most tenuous of evidence, such as assertions of an empirically resolvable increase in the frequency or violence of tropical storms or extreme weather events, while ignoring and shouting down any related extrapolation of benefits, even when they are backed by rather solid evidence (such as, almost the entire literature on the subject of the effect of carbon dioxide on plant growth).
I don't know what your profession might be, NeutronCowboy, but if it is a scientific one you might meditate on the importance of maintaining an open and balanced mind when considering even things you feel very strongly about. I'm just sayin'...