Element in National Trust into reforming tourism (9)
I believe the answer is:
strontium
'element' is the definition.
(strontium is a kind of element)
'national trust into reforming tourism' is the wordplay.
'national trust' becomes 'nt'.
'into' indicates putting letters inside.
'reforming' indicates an anagram.
'tourism' is an anagram of 'stroium'.
'nt' placed within 'stroium' is 'STRONTIUM'.
'in' is the link.
(Other definitions for strontium that I've seen before include "Element with symbol Sr" , "Soft metallic element" , "Metal" .)