Quotes below, sources below that: - CO2 increased leaf area, water use efficiency, and harvest index (in tomatoes) [1] - Optimal levels for tomatoes may be 2 to 5 times the normal atmospheric levels (1000 to 1500 ppm CO2 versus ambient levels of 350 ppm) [2] - Combining increases in CO2 with fertilization and irrigation could greatly enhance leaf area which when coupled to observed increases in net photosynthesis as a result of elevated CO2 could greatly increase productivity of loblolly pine trees. [3] - demonstrating an optimal CO2 concentration of 889.6, 909.4, and 894.2 ppm for aboveground, belowground, and total biomass, respectively, and 967.8 ppm for leaf photosynthesis (in winter wheat) [4]
[1] https://www.sciencedirect.com/science/article/abs/pii/S03783... [2] https://cals.arizona.edu/hydroponictomatoes/nutritio.htm [3] https://link.springer.com/article/10.1007/s004680050111 [4] https://pubmed.ncbi.nlm.nih.gov/26253981/