Petunia and pansy reactions to prolonged carbon dioxide enrichment

Although crops often respond immediately to enriched CO₂ concentrations (e.g., increased photosynthesis), this initial response is often not sustained throughout production, thus reducing the benefit of this input. For horticulture species, the timing and extent of these acclimation responses are still widely uncertain.

The objective of a new study was to determine species-specific acclimation responses to elevated CO₂ concentrations for pansy (Viola ×wittrockiana "Matrix Blue Blotch Improved") and petunia (Petunia ×hybrida "Dreams Midnight"). The research is published in the Journal of the American Society for Horticultural Science.

Although the average ambient CO₂ concentration currently exceeds 400 μmol⋅mol−1, concentrations in the greenhouse environment commonly decrease to less than 200 μmol⋅mol−1 during production in the winter and early spring. However, the current atmospheric concentration does not maximize photosynthetic capacity; therefore, there is potential to enhance plant growth by enriching controlled environments with CO₂.

Studies have shown that CO₂ concentrations between 800 and 1200 μmol⋅mol−1 have great potential to increase plant growth, with concentrations more than 900 μmol⋅mol−1 nearly eliminating photorespiration. However, previous studies have established that the most practical CO₂ concentration range for most species is 600 to 1000 μmol⋅mol−1. Early short-term studies showed that an economically efficient way to enhance ornamental plant growth in controlled environments was to increase the CO₂ concentration within this target range.

Although responses of horticulture species to long-term elevated CO₂ concentrations continue to be studied, further research is needed to identify the timing and extent of these species-specific responses to better understand CO₂ as an input for controlled environment production. An increase in biomass was observed for both petunia "Dreams Midnight' and pansy "Matrix Blue Blotch Improved' under an elevated CO₂ concentration compared with ambient conditions at all days, but physiological acclimation to this input within 7 d of production likely limited the potential of this increase in biomass.

However, the results are constrained to the environmental conditions and container limitations used for this study, with the potential for sink limitations and interactions with other production inputs (e.g., temperature, nutrition) warranting further research to explain responses to elevated CO₂ concentrations for a diverse array of horticulture species. With this information, improved strategies for CO₂ enrichment that bypass acclimation limitations may be developed, which could increase production efficiency for controlled environments.