Seasonal Change. Environmental Explorations. Mr. Velazquez. Why the change?. As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter. During winter, there is not enough light or water for photosynthesis.
During the summer the phosphate are at a very high level. The chlorophyll is the most abundant pigment.
In fall the phosphate levels alone with other chemicals and nutrients moves from the leaf into the stem of the plant.
This leads to the production of other pigments like Anthocyanins.