CO2 is a key constituent of the plant growth-promoting volatiles generated by bacteria in a sealed system.

Plant growth is greatly inhibited in tightly sealed Petri dishes for lack of CO 2 . Bacteria which co-cultured with plant can produce CO 2 to promote plant growth in sealed systems. Bacteria produce a wide variety of volatiles, some of which can support and others can damage plant growth. It is a controversial issue whether CO2 or other bacterial volatile compounds promote plant growth in sealed systems. CO2 is critical for photosynthesis. Here, we show that CO2 is a key constituent of the plant growth-promoting volatiles generated by bacteria in a sealed system. We revealed that the growth of Arabidopsis seedlings in an airtight container was retarded due to insufficient supply of the CO2. When either CO2 was introduced into the container, or the seedlings were co-cultured along with certain bacterial species, the plants’ growth was restored. Conclusion: The benefit of co-culturing was largely due to the CO2 generated by respiration of the bacteria.