Phosphorus Deficiency

From the Hort 402 manual

Phosphorus deficiency tends to inhibit or prevent shoot growth. Leaves turn dark, dull, blue-green, and may become pale in severe deficiency. Reddish, reddish-violet, or violet color develops from increased anthocyanin synthesis. Symptoms appear first on older parts of the plant. New leaves usually appear healthy, but they are often small. Phosphorus deficiency also leads to increased root to shoot ratio in many plant species.

Symptoms

• Dark green leaves
• Small leaf size
• Reduced shoot growth and increase root growth result in a low shoot/root ratio.

Processes

P deficiency is common in nature. Plants have evolved a number of responses:

• hormonal stimulated root growth
• increased shallowness of root systems
• reduce shoot growth through regulated water stress induced by closing of aqua pores in the root system