What causes tree leaves to change color in the fall?

Tree leaves change color in the fall primarily due to the breakdown of chlorophyll, the pigment responsible for the green color in leaves. As the seasons shift from summer to fall, temperatures drop and daylight decreases, signaling trees to prepare for winter. In response to these environmental changes, chlorophyll production slows down and eventually ceases.

As chlorophyll breaks down, it diminishes in quantity, allowing other pigments present in the leaves to become more visible. These pigments, such as carotenoids (which produce yellow and orange hues) and anthocyanins (which can generate red and purple shades), were always present but masked by the dominant green of chlorophyll during the growing season. This process highlights the vibrant colors of fall foliage, creating the stunning displays often seen during autumn.

The other choices are less relevant because they do not accurately explain the visible color change observed. While chlorophyll production is reduced, the key aspect is its breakdown. Decreased photosynthesis activity is a consequence of decreased sunlight and temperatures but does not directly cause the color change itself. Lastly, absorption of moisture is unrelated as it does not directly affect the pigments within the leaves during this seasonal change.