Interaction between plant species and substrate type in the removal of CO2 indoors

Elevated indoor concentrations of carbon dioxide (CO2) cause health issues, increase workplace absenteeism, and reduce cognitive performance. Plants can be part of the solution, reducing indoor CO2 and acting as a low-cost supplement to building ventilation systems. Our earlier work on a selection of structurally and functionally different indoor plants identified a range of leaf-level CO2 removal rates, when plants were grown in one type of substrate. The work presented here brings the research much closer to real indoor environments by investigating CO2 removal at a whole-plant level and in different substrates. Specifically, we measured how the change of growing substrate affects plants’ capacity to reduce CO2 concentrations. Spathiphyllum wallisii ‘Verdi’, Dracaena fragrans ‘Golden Coast’, and Hedera helix, representing a range of leaf types and sizes and potted in two different substrates, were tested. Potted plants were studied in a 0.15-m3 chamber under ‘very high’ (22,000 lx), ‘low’ (~ 500 lx), and ‘no’ light (0 lx) in ‘wet’ (> 30%) and ‘dry’ (< 20%) substrate. At ‘no’ and ‘low’ indoor light, houseplants increased the CO2 concentration in both substrates; respiration rates, however, were deemed negligible in terms of the contribution to a room-level concentration, as they added ~ 0.6% of a human’s contribution. In ‘very high’ light, D. fragrans, in substrate 2, showed potential to reduce CO2 to a near-ambient (600 ppm) concentration in a shorter timeframe (12 h, e.g. overnight) and S. wallisii over a longer period (36 h, e.g. weekend).