From Setpoints to System Dynamics: Integrating Light, CO2 and Fertigation in Controlled-Environment Agriculture

Controlled-environment agriculture (CEA) allows growers to regulate temperature, humidity, light, nutrients and root-zone parameters with high precision. However, precision alone does not guarantee improved performance when each control variable is interpreted in isolation, because plants respond to these inputs as an integrated system. Light controls both photosynthetic activity and photomorphogenic signalling. CO2 changes carbon assimilation, stomatal behaviour, water use and source-sink relations. Fertigation variables such as individual macro- and microelement concentrations, electrical conductivity (EC), pH, and nutrient solution flow rate determine nutrient availability, plant development, osmotic status, oxygen delivery and root-zone signalling. In plants, these inputs converge on shared physiological and molecular processes, including carbon–nitrogen balance, transpiration-driven nutrient delivery, nitrate and phosphate uptake, H+-ATPase activity, hormone signalling, root architecture, and sink development. This narrative review proposes a qualitative, conceptual systems-dynamics framework; it does not present a calibrated simulation or validated control model. The central proposition is that plant growth, yield and fruit quality emerge from feedback loops among carbon capture, nutrient acquisition, hydraulic function and developmental sink strength. In crops such as cucumber, tomato, lettuce, strawberry, pepper and basil, the same environmental input can improve one trait whilst weakening another, depending on developmental stage, cultivar, sink demand, and root-zone conditions. A system-dynamics framework is therefore essential for designing production strategies that synchronise light settings, CO2 schedules and fertigation regimes with plant physiological stages. For compact cucurbits and other commercial CEA crops, this approach can help optimise productivity per unit volume whilst maintaining nutrient status, water-use efficiency and fruit quality. These insights also apply to CEA for long-term space, Moon and Mars missions.