The decrease in concentration of potassium ions leads to increase in turgidity of the guard cells.

Explanation

**Step-by-Step Solution:**

1. **Understanding Guard Cells and Turgidity:**
- Guard cells are specialized cells that surround the stomata (pores) in plant leaves. They regulate the opening and closing of these stomata, which is crucial for gas exchange and transpiration.

2. **Role of Potassium Ions:**
- Potassium ions (K+) play a significant role in the turgidity of guard cells. When potassium ions accumulate inside the guard cells, they cause water to enter the cells through osmosis.

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