Effects of different concentrations of CO2 in the atmosphere of in vitro culture ‎vessels on growth characteristics and photosynthetic capacity of Epipactis ‎veratrifolia

Epipactis veratrifolia is a terrestrialorchid that belongs to thetemperate zones of Iran with great breeding potentials for ornamental usages. Although in vitro propagation of this orchid has been previously performedbut investigation on factors influencing its in-vitro growth and photosynthesis is still needed. In the current study, three-leaflet seedlings were cultured in closed vessels containing modified Fast liquid medium together with sterilized perlite (for sample establishment). To remove CO2, vials containing saturated KOH solution as CO2 absorbent and to increase CO2 concentrations, vials containing 3 mL CO2-releasing solutions (3 M sodium bicarbonate and sodium carbonate) were placed into the culture vessels. The experiment was carried out based on a completely randomized design with three replications and three samples per each replicate. Growth parameters including fresh and dry weights of shoot, stem height and root length together with transpiration rate and maximum quantum yield of photosystem II efficiency (QYmax) of the samples were measured. The highest values for shoot height, shoot dry and fresh weights and root length were observed in CO2-increased treatments. Removing CO2 from the atmosphere of culture vessels caused a dramatic decrease in QYmax of plantlets in vitro. Meanwhile, following desiccation, higher transpiration rate was detected in control and CO2-increased treatments, while removing CO2 decelerate transpiration rate of the plantlets. In conclusion, with increasing CO2 in vitro we can promote photosynthetic efficiency of Epipactis veratrifolia and as a result enhance growth of plantlets in vitro.