You may have to copy the root generated keys in the .ssh directory of your apache user.
Assuming the homedir of apache is /var/www (check /etc/passwd) and the named key is id_rsa-git :
mkdir -p /var/www/.ssh/
cp /root/.ssh/id_rsa-git /var/www/.ssh/id_rsa
No need to copy the public key.
Note : by default the key used are id_rsa or id_dsa. You may change the name of the copied key to match this.
You may also change ownership of the id_rsa key and .ssh directory:
chown -R apache:apache /var/www/.ssh
chmod 0700 /var/www/.ssh
chmod 0600 /var/www/.ssh/id_rsa