Ephemeral nature of rotting nectarines (10)
I believe the answer is:
'ephemeral nature' is the definition.
(quality or condition of being ephemeral)
'rotting nectarines' is the wordplay.
'rotting' is an anagram indicator.
'nectarines' with letters rearranged gives 'TRANSIENCE'.
'of' is the link.
(Other definitions for transience that I've seen before include "Ephemerality" , "Impermanence" .)