Trainee giving nitrogen to plant (6)
I believe the answer is:
intern
'trainee' is the definition.
(intern can mean a trainee worker)
'nitrogen to plant' is the wordplay.
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'to' says to put letters next to each other (I've seen this in other clues).
'plant' becomes 'inter' (to inter in the ground).
'n' after 'inter' is 'INTERN'.
'giving' is the link.
(Other definitions for intern that I've seen before include "Official language of Pakistan" , "Novice gaining experience" , "Hold in custody" , "Confine as a prisoner" , "Imprison without trial - hospital junior doctor" .)