One has doubts about short stick holding mushroom (7)
I believe the answer is:
sceptic
'one has doubts' is the definition.
(I've seen this before)
'short stick holding mushroom' is the wordplay.
'short' means to remove the last letter.
'holding' means one lot of letters goes inside another.
'mushroom' becomes 'cep' (name for Boletus edulis - an edible mushroom).
'stick' with its last letter taken off is 'stic'.
'stic' going around 'cep' is 'SCEPTIC'.
'about' is the link.
(Other definitions for sceptic that I've seen before include "Doubter; atheist" , "He's hard to convince" , "I may doubt that" , "Person who doubts the truth" , "One questioning accepted opinions" .)