Space in rising open land (4)
I believe the answer is:
room
'space' is the definition.
(room is a kind of space)
'rising open land' is the wordplay.
'rising' shows that the letters should be reversed in order (going up in a down clue).
'open land' becomes 'moor' (I've seen this before).
'moor' in reverse letter order is 'ROOM'.
'in' is the link.
(Other definitions for room that I've seen before include "See 17" , "kitchen?" , "See 1" , "Place" , "Opportunity, scope" .)