plant_nutrition → essential → oxygen
Oxygen is required for respiration (energy production) in all living tissues, especially roots. It is also part of most plant organic compounds.
Oxygen deficiency is most commonly a root-zone aeration problem: - Wilting despite wet media - Poor root growth, brown/black roots - Reduced nutrient uptake and stunting - Increased susceptibility to root pathogens
Not a classic nutrient toxicity. Reactive oxygen species are a stress response rather than a fertiliser issue.