All of the following can cause yellowing of leaves in plants except:

The correct answer is related to the role of phosphorus in plant health. While nitrogen and light levels are critical for chlorophyll production and overall plant vigor, phosphorus primarily plays a role in energy transfer and photosynthesis rather than directly affecting the leaf coloration in the same way nitrogen does.

Inadequate nitrogen levels typically lead to chlorosis, or yellowing of leaves, because nitrogen is essential for chlorophyll production. Overwatering and lack of light also have direct impacts on leaf health: excessive water can suffocate roots and lead to nutrient deficiencies, while insufficient light prevents plants from performing photosynthesis adequately.

On the other hand, an excess of phosphorus, while potentially leading to other issues such as nutrient imbalances, does not generally cause yellowing in leaves. Plants can often tolerate higher levels of phosphorus, making it less directly associated with chlorotic symptoms compared to the other factors listed. Hence, too much phosphorus is the correct answer in the context of what does not cause leaf yellowing.