Given this generic serialization code:
public virtual string Serialize(System.Text.Encoding encoding)
{
System.IO.StreamReader streamReader = null;
System.
If you just want to remove the namespace aliases, then as already shown you can use XmlSerializerNamespaces to force XmlSerializer to use the namespace explicitly (i.e. xmlns="blah") on each element, rather than declaring an alias and using the alias instead.
However, regardless of what you do with the aliases, the fundamental name of that element is REQUEST_GROUP in the Com.Foo.Request namespace. You can't remove the namespace completely without that representing a breaking change to the underlying data - i.e. somebody somewhere is going to get an exception (due to getting data it didn't expect - specifically REQUEST_GROUP in the root namespace). In C# terms, it is the difference between System.String and My.Custom.String - sure, they are both called String, but that is just their local name.
If you want to remove all traces of the namespace, then a pragmatic option would be to edit away the Namespace=... entries from [XmlRoot(...)] and [XmlType(...)] (plus anywhere else that isn't shown in the example).
If the types are outside of your control, you can also do this at runtime using XmlAttributeOverrides - but a caveat: if you create an XmlSerializer using XmlAttributeOverrides you must cache and re-use it - otherwise your AppDomain will leak (it creates assemblies on the fly per serializer in this mode, and assemblies cannot be unloaded).