B. Are there Laboratory Tests Showing Plants Improve with Higher CO2 Levels?

An investigation showed a side by side comparison of orchid plantlets one group exposed to 350ppmv CO2 and a group exposed to 1000 ppmv.  After 3 months, the group exposed to the 1000 ppmv showed enhanced root grown and a higher root shoot ratio.  The overall enrichment was a 2 fold increase in matter production.  It also resulted in higher sugar and starch content.  The overall conclusion is that the higher CO2 was highly beneficial to the plant grown and health under stressful field conditions.  [Gouk S.et al (1999) Changes in photosynthetic capability and carbohydrate production in an epiphytic CAM orchid plantlet exposed to super-elevated CO2, Environmental and Experimental Botany, Vol 41. Issue 3, pgs. 219-230.]

Another investigation compared sweetgum trees subjected to varying levels of CO2 starting at 350 ppmv up to 30,000 ppmv.  Sweetgum trees are commercially used in paper production.  The tree growth in all respects (leaves, roots, length) improved with increasing CO2 concentration until 30,000 ppmv.  At 30,000 ppmv there was a reduction. The largest improvement was at 10,000 ppmv.  [Tisserat, B (2005) Establishing Tissue Cultured Sweetgum Plants in Soil, HortTechnology Vol 15 (2) pgs. 308-312.]

A comparative study was done for various grass species at CO2 levels starting at 400 and ending at 1200 ppmv.  The amount of biomass increased for all grass species up to 1000 ppmv.  After 1000 ppmv it continued to increase for Kentucky bluegrass and perennial ryegrass, but went down for tall fescue.  The biomass increases were substantial ranging from 32% for Kentucky bluegrass, 22% for perennial ryegrass, and 35%for tall fescue.  [Zheng, Y et al (2018) The optimal CO2 concentrations for the growth of three perennial grass species, BMC Plant Biology 18:27, pgs. 1-12] 

A review of various studies on plant responses to rising CO2 concentrations show that concentrations up to 1000 ppmv will result in higher growth, decreased water use, and decreased need for nitrogen.  [Taub, D. (2010) Effects of Rising Atmospheric Concentrations of Carbon Dioxide on Plants, Nature Education Knowledge 1(8):21]