how parse xml with many roots on php

I wanna read a XML but this XML have many roots in the same XML:

[obtenerResult] => 
<?xml version="1.0" encoding="utf-8"?>
   <node1>
     <node2></node2>
   </node1>
<?xml version="1.0" encoding="utf-8"?>
<node4>
    <node5></node5>
</node4>

How can read the nodes with simplexml on PHP.

I try $rXML=simplexml_load_string($result->obtenerResult->node4); but dont working

Thank you for your help.