Which of the following is a primary function of potassium in plants?

Potassium plays a crucial role in regulating the opening and closing of stomates, which are tiny pores on the surface of leaves. This regulation is vital for maintaining a plant's water balance and enabling gas exchange during photosynthesis and respiration. When potassium ions are concentrated in the guard cells surrounding the stomates, they cause these cells to swell, leading to the opening of the stomates. Conversely, when potassium levels fall, the guard cells lose turgor pressure, resulting in stomatal closure. This process is essential for allowing plants to conserve water during periods of drought while still enabling the necessary gas exchange for photosynthesis.

The other functions, while essential for overall plant health, do not primarily involve potassium. For instance, photosynthesis enhancement is largely attributed to chlorophyll and light, nitrogen fixation is a process mainly associated with certain bacteria and legumes, and root development is more influenced by other nutrients such as phosphorus. With this understanding, the role of potassium in stomatal regulation is clearly a primary function that directly impacts plant health and performance.