What occurs if a plant lacks sufficient nitrogen (in nitrates)?

When a plant lacks sufficient nitrogen, particularly in the form of nitrates, a common symptom is the yellowing of older leaves, a condition known as chlorosis. Nitrogen is a crucial element for plant growth as it is a key component of chlorophyll, the molecule that plants use for photosynthesis. When there is an insufficient supply of nitrogen, the plant cannot produce enough chlorophyll, leading to a decline in photosynthesis efficiency. As a result, the older leaves, which are often the first to show deficiency symptoms, begin to turn yellow while the newer growth may still appear healthy. This response occurs because the plant reallocates its limited resources to support newer growth.

In contrast, the other options may imply changes in the plant's growth or reproductive success that are not generally associated with nitrogen deficiency. For example, blooming earlier or increased fruit bearing typically suggest good nutrient availability rather than a deficiency. Similarly, a lack of nitrogen usually restricts growth rather than promotes it, as nitrogen is essential for overall growth and vigor.