Suitability of foliage plants for indoor decoration based on CO₂ emission and absorption rate and stomata density

Use of foliage plants for indoor decoration is pursuing tradition in several cultures. With contemporary living patterns, frequent replacement of indoor plants has become impractical. Therefore, this experiment was conducted to identify indoor plants with low carbon dioxide (CO2) emission or CO2 absorption ability in nights to be kept continuously indoors. Five common indoor plants (Cryptanthus sp., Dieffenbachia seguine, Dracaena sanderiana, Sansevieria trifasciata and Zamioculcas zamiifolia) were placed separately in 1000 L airtight chambers for 12 h in the dark. The CO2 level in each chamber was measured before and after the experiment and the difference was calculated. The stomatal count of both adaxial and abaxial surfaces was taken in each plant type to determine the relationship between CO2 emission/absorption efficiency and stomatal density of tested ornamental species. From the test plant species, D. seguine, D. sanderiana and Z. zamiifolia, showed positive CO2 equilibrium in the chambers and the CO2 increments were 0.16 ppm cm-2, 0.39 ppm cm-2 and 0.18 ppm cm-2 of leaf area, respectively. Both Cryptanthus sp. and S. trifasciata showed negative CO2 equilibrium at around -0.20 ppm cm-2 of leaf area. Sansevieria trifasciata and D. sanderiana possessed stomata in both adaxial and abaxial surfaces, while stomatal number in adaxial surface of other three test plant species was negligible. The average number of stomata Cryptanthus sp. was 5.56x10⁴ cm⁻2, D. seguine 5.03x10⁴ cm⁻2, D. sanderiana 9.05x10⁴ cm⁻2, S. trifasciata 5.25x10⁴ cm⁻2 and Z. zamiifolia 3.51x10⁴ cm⁻2. Stomata in Cryptanthus sp. and S. trifasciata close during day time and open at night. Present study concludes that potted Cryptanthus sp. and S. trifasciata (plants with CAM photosynthesis pathway) used for indoor decoration absorb CO2 during the night, and hence, are safe to keep indoors during day and night.