Elevated carbon dioxide positively influences biomass and specialized metabolites of <i>Stevia rebaudiana</i> Bertoni under high density horizontal farming

Stevia produces steviol glycosides, which are non-caloric natural sweeteners that are helpful in diabetics. Environmental and agronomic practices play an important role in plant productivity. However, there is a lack of information on stevia productivity under an elevated CO2 (eCO2) and planting density. Therefore, the current research was performed with the objective of evaluating the effect of eCO2 and planting density on the stevia biomass and specialized metabolites. The study used a nested design with randomized complete block design (RCBD) in four blocks with two factors (CO2 and planting density). Factor A, 'Carbon dioxide' (CO2) with two levels [eCO2 and aCO2 (ambient CO2], was applied across the block. In comparison, Factor B, with three levels- High-density Vertical (HDV), High-density horizontal (HDH) and Low-density horizontal (LDH)- were nested in Factor A (CO2). All the data were analyzed using an analysis of variance (ANOVA) of the SAS (9.4), and the mean were separated for significant differences using the least significant differences (LSD) test at P≤ 0.05. The study's results showed that eCO2 increased the total dry biomass, despite the density. However, a higher biomass was achieved from the HDV and HDH compared to the LDH. eCO2 treated plant produced significantly higher flavonoid by 17%, 24%, and 15% at the 2nd, 3rd, and 4th month of planting (MAP). A similar trend was seen for the phenolic content. Steviosides and rebaudiosides A significantly increased with eCO2. Under aCO2, no significant differences were seen for steviosides at the 2nd and 4th MAP, while at the 3rd MAP, HDV was observed with a significantly low value. Under eCO2, the HDV had significantly low values for steviosides with no difference in the LDH and the HDH throughout the growth period. The finding indicates that eCO2 positively enhances the biomass and specialized metabolites regardless of the densities. However, the LDH and the HDH performed better than the HDV on individual plant base performance in terms of specialized metabolites.