Spirit of staff having mushroom turnover (7)
I believe the answer is:
spectre
'spirit' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
(Other definitions for spectre that I've seen before include "something seen as a threat" , "'Phantom, shade (7)'" , "Enemy organisation for James Bond; ghost" , "after-image?" , "spirit" .)