Carbon deficit is a condition where a plant fixes less carbon through photosynthesis than it uses for respiration and growth. This occurs when light, CO₂ concentration, or leaf area is insufficient to meet the plant’s metabolic demand.
In indoor and outdoor growing, carbon deficit is most often driven by low light intensity, reflected in inadequate PPFD and low DLI, which limits sugar production. Prolonged deficit leads to slow growth, reduced vigor, leaf drop, and eventual decline as the plant consumes stored carbohydrates to survive.
Carbon deficit contrasts with carbon surplus, where photosynthesis exceeds demand and excess sugars are stored or used for new growth. Environmental balance, especially light and CO₂ availability, determines which state a plant operates in.
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