What will be the effect of the accumulation of K^ + ions in guard...

When the amount of solutes increases, osmotic potential decreases, and total water potential decreases.

Opening and closure of the stomatal pore are mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of it. Guard cells have cell walls of varying thickness and differently oriented cellulose microfibers, causing them to bend outward when they are turgid, which in turn, causes stomata to open.

Stomata open when there is an osmotic gain of water, occurring from the inflow of $K^{+}$ ions from neighboring cells.