Study: Optimized CO2 and Ventilation Boost Cannabis Micropropagation Biomass by Up to 282%

A new study published in the journal Industrial Crops and Products finds that carefully balancing carbon dioxide levels and air exchange dramatically improves the growth and physiological performance of medicinal cannabis plantlets grown through photoautotrophic micropropagation (PAM). Researchers from China Agricultural University and the Ministry of Agriculture and Rural Affairs in China evaluated two CBD cultivars, ‘Charlotte’ and ‘Auto Charlotte’, under varying CO2 concentrations and air change rates (ACR). PAM replaces sugar in tissue culture media with CO2 as the sole carbon source, encouraging plants to rely on photosynthesis rather than external sugars.

The study compared ambient CO2 levels of 400 μmol mol−1 with elevated levels of 800 μmol mol−1, alongside four ventilation rates ranging from 0.7 to 13.6 air exchanges per hour. While raising CO2 consistently improved plant height, leaf area, biomass, root vigor and photosynthetic performance, the most significant gains occurred when elevated CO2 was paired with a moderate ACR of 4.4 h−1.

Under this optimized combination, dry weight increased by 181% in ‘Charlotte’ and 124% in ‘Auto Charlotte’ compared to conventional conditions. Root fresh weight in ‘Charlotte’ rose by more than 1,000%, while total biomass increased by 282%. Net CO2 exchange, a key measure of photosynthetic performance, climbed by as much as 733% to 943% compared to baseline conditions.

However, excessive ventilation reduced water retention in the growing substrate, triggering drought stress and suppressing growth. At the highest air exchange rate, water content in the substrate fell by up to 82%, contributing to drought stress that was associated with reduced chlorophyll levels and impaired root development.

The researchers conclude that combining an ACR of about 4.4 h−1 with 800 μmol mol−1 CO2 provides a practical, industry-ready protocol for producing vigorous, sugar-free cannabis plantlets. As they state, “increasing CO2 availability in culture vessels, through increased CO2 enrichment and air exchange, significantly enhanced carbon assimilation, growth and overall plantlet quality of medicinal cannabis.”

They found that raising the ACR from 0.7 to 4.4 h−1 “significantly enhanced biomass accumulation in both cultivars,” while pushing ventilation higher to 13.6 h−1 “markedly reduced water content in the substrate medium, thereby inducing drought stress” and suppressing growth. Increasing CO2 levels in the culture room to 800 μmol mol−1 “further enhanced the Total NCEA thus biomass accumulation and improved overall plantlet quality.”

Based on these findings, the team writes, “we recommend using culture vessels with an ACR of approximately 4.4 h−1 combined with elevated CO2 concentration in the culture room, to optimize growth and rooting of medicinal cannabis plantlets in PAM.” They note that the improvements were achieved using passively ventilated vessels, avoiding the cost and contamination risks associated with forced aeration systems.

The full study can be found by clicking here.