Phosphorus deficiency in plants is typically indicated by which symptom?

• A. Yellowing older leaves
• B. Purplish or dark green leaves
• C. Leaf margins scorched/browned
• D. Brown spots on leaves

Answer: (B)

Phosphorus deficiency shows up as a purplish or dark green tint on the leaves, often starting with the older foliage. Phosphorus is mobile in the plant, so when it's lacking, the plant shifts available phosphorus to new growth and the affected, older leaves display the color change as a stress response. This purple coloration helps distinguish it from other nutrient problems: nitrogen deficiency typically causes yellowing of older leaves, potassium deficiency tends to scorch leaf margins, and brown spots on leaves point to various diseases or other issues. So, the purple or dark green leaves are the clearest clue that phosphorus is the limiting nutrient.