[Advaita-l] Question on a shloka on Rudram

[Krishna Subrahmanian]

Anybody who knows and has the time:


vR^kshasya mUla sekena shAkA puShyanti vai yathA |
shivE rudra japaath prIte, prItA evAsya devatAhA ||

This is a generally quoted praise for Rudra Japa.  I understand most of the verse.  In this line what does "asya" exactly refer to i.e. kasya and what does it qualify?  I would have thought the word "anena" would have been used to say "by this (japa)" all devataas are pleased.

Your help is appreciated.

Regards,
K