Orchid Responses to Super-High Atmospheric CO₂ Enrichment

According to Norikane et al., "the genus Cymbidium comprises about 50 species distributed in tropical and subtropical Asia and Oceania," and "almost all cultivated cymbidiums are hybrids, thin-leaved and with a C₃ mode of photosynthesis." In addition, "Cymbidium was the first orchid genus to be propagated using shoot-tip culture." In the present study, the authors obtained Cymbidium (Music Hour 'Maria') shoots with two to three leaves from a mass of protocorm-like bodies derived from shoot-tip culture and were further cultured in vitro on modified Vacin and Went medium in air augmented with either 0, 3000 or 10,000 ppm CO₂under photosynthetic photon flux densities of either 45 or 75 µmol m^-1 s^-1 that were provided by cold cathode fluorescent lamps for a period of 90 days, after which they were transferred to ex vitro culture for an additional 30 days.

In so doing, the authors found that, relative to plants grown in vitro in ambient air, the percentage increases in shoot and root dry weight due to enriching the air in which the plants grew by 3000 ppm CO₂were, respectively, 216% and 1956% under the low light regime and 249% and 1591% under the high light regime, while corresponding increases for the plants grown in air enriched with an extra 10,000 ppm CO₂were 244% and 2578% under the low light regime and 310% and 1879% under the high light regime. Similarly, in the ex vitro experiment, percentage increases in shoot and root dry weight due to enriching the air in which the plants grew by 3000 ppm CO₂were, respectively, 223% and 436% under the low light regime and 279% and 469% under the high light regime, while corresponding increases for the plants grown in air enriched with an extra 10,000 ppm CO₂were 271% and 537% under the low light regime and 332% and 631% under the high light regime. Based on these results, the four Japanese researchers concluded that "super-elevated CO₂enrichment of in vitro-cultured Cymbidium could positively affect the efficiency and quality of commercial production of clonal orchid plantlets."