A frequent talking point by global warming deniers is that CO2 in the atmosphere is actually beneficial because "CO2 is plant food". I'm a non biologist trying to figure out under what circumstances this is actually true.

Here are my thoughts so far:

  • Plant growth is more or less governed by Liebig's law of the minimum - the plant needs sunlight, CO2, water, nutrients in a certain composition, whatever is lacking limits growth
  • In addition to it's role in photosynthesis, water is needed to transport nutrients from the soil, so dry conditions can limit effective nutrient availability
  • The energy needed to assimilate CO2-carbon is independent of the CO2 concentration
  • The rate of photosynthesis is (within the limits given by energy etc.) governed by CO2 concentration and active plant matter
  • photosynthesis only works in a more or less narrow temperature band

From this, it follows that a higher CO2 concentration in air will boost plant growth only if everything else (light, water, nutrients) is abundant.

So I have two interconnecteed questions:

  • How wrong is my simplistic view, does my conclusion hold?
  • What do we actually observe in the wild or in experiments?
  • $\begingroup$ Possible duplicate of biology.stackexchange.com/q/681/3340 $\endgroup$ – WYSIWYG Jul 1 '16 at 10:30
  • $\begingroup$ Definitly helpful. Need some time to read linked papers in the answers over there. $\endgroup$ – mart Jul 1 '16 at 10:37
  • $\begingroup$ @mart In brief: High CO2: Toxic effect. Photosynth rate drop. Stomata closes. Medium CO2: Optimum photosynth. Low CO2: photosynth rate drastic fall in C3. in C4 plant, fall not so drastic. Very Low CO2: C3 stop photosynth, enter "photorespiration". C4 very low rate photosynth. $\endgroup$ – Always Confused Aug 19 '16 at 10:52

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