Undergravel Filtration

Please note that I do not have an e-mail address right now.
I have always learnt that plant growth suffers in tanks
using undergravel filtration.
Yet I have seen several messages from aquarists who seem to
be getting lush plant growth while using undergravel filters.
They also seem to give the impression that the undergravel filter 
may be contributing nutrients to the substrate (while heating the substrate) hence avoiding the
use of substrate heating coils.