Physiological responses of basil to low oxygen availability in soilless culture

Soilless cultivation systems in controlled environment agriculture create varying rootzone oxygen conditions, which can impact biomass production. The present study investigates the effect of mild hypoxia and its effect on shoot biomass production, root anatomy and architecture of basil (Ocimum basilicum L.) in ebb-flood, deep-water, and aeroponic systems in a greenhouse. After 4–5 weeks, aeroponically grown plants produced greater shoot biomass than those in the ebb-flood system, although root dry weights did not differ significantly. Using optical coherence tomography (OCT), we non-destructively quantified aerenchyma formation, confirming the suitability of OCT for imaging living root tissues. Aerenchyma developed 14–21 days after transplanting and were more extensive in unaerated deep-water systems than in aerated or aeroponic systems. Ethylene emission 20 days after transplanting did not differ between treatments. Thus, basil shows adaptative responses at mild hypoxia, which can lead to yield losses. This emphasises the need to define rootzone oxygen thresholds.