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).