This line shows us what happens after the early leaf is no longer figuratively a flower—it becomes a true leaf. But the speaker doesn't say "becomes," he says "subsides." This means that the first leaf sank down, or settled, to become another leaf.
The use of the word "subsides" implies that the speaker thinks that the first leaf—the flower of sorts—was better than the actual leaf. The first leaf had to stoop down, or lower itself, to become the second one.
Going with our two interpretations, this means that either spring blooms and flowers are more beautiful than the full leaves of summer, or that leaves in the early morning are much prettier than leaves at, say, midday.