Agronomy Degree Practice Exam

Which visual sign is commonly associated with phosphorus deficiency?

1. Curling leaves

2. Purple leaves

3. Striped yellow leaves

4. Yellow leaves

The correct answer is: Purple leaves

Phosphorus deficiency in plants is typically characterized by a darkening of the foliage, which often leads to a purpling, especially in the older leaves. This purpling occurs because phosphorus is vital for several key physiological processes, including energy transfer and photosynthesis. When plants lack sufficient phosphorus, the production of anthocyanins, which are pigments responsible for the purplish color, increases as a stress response. In contrast, other visual signs associated with different nutrient deficiencies or environmental stresses lead to different leaf symptoms. Curling leaves may indicate water stress or other nutritional deficiencies but are not specific to phosphorus. Striped yellow leaves are generally seen in cases of nitrogen deficiency or specific pest damage. Yellow leaves, often a sign of nitrogen deficiency or iron chlorosis, do not signify a phosphorus issue. Therefore, the presence of purple leaves is a distinct and recognizable symptom that points specifically to phosphorus deficiency in plants.