The bloom, whose petals nipp'd before they blew Died on the promise of the fruit, is waste; The broken lily lies--the storm is overpast. (52-54)
Shelley often uses flowers to symbolize mankind. Like the destruction of a lily, the death of Adonais is a loss for the world. Both are a tragedy, in his eyes.
Afar the melancholy thunder moan'd, Pale Ocean in unquiet slumber lay, And the wild Winds flew round, sobbing in their dismay. (124-126)
The elements are sympathetic to man, and mourn the loss of the youth. Shelley uses personification to give them feelings that mirror his own. Ever notice how, when you are sad, even a pretty flower can seem mournful?
Grief made the young Spring wild (136)
Even the seasons are bummed out about losing Adonais. He gives these seasons proper names to show that they are indeed characters in the poem, with separate feelings and motives.
The airs and streams renew their joyous tone; The ants, the bees, the swallows reappear; (156-157)
To the speaker, the renewal of life in the spring seems to give the air and streams a "joyous" feeling. This imagery of bubbling streams, bugs, and birds shows that life is beginning again after a hard winter.
Through wood and stream and field and hill and Ocean A quickening life from the Earth's heart has burst As it has ever done, with change and motion (163-165)
In the poem, nature is always moving, changing, and renewing itself. It's full of life, says Shelley, and it always will be. He emphasizes the natural world's eternal nature frequently in the poem to remind readers that death is just part of the cycle.