Configuring Local and JTA Transaction in Spring based Appplication using JPA

Issue

• Spring based applications using JPA having web service which uses 2 datasources which don't require JTA since there is no distributed transaction across the 2 databases.
  The transactions are local to each of the databases. By using JPA for persistence and persistence.xml has non-jta datasource configured and transaction_type is set to local.
  When configured this way, persistence doesn't happen. Only after switching to a JTA transaction manager and using JTA datasource in persistence.xml, the persistence does happen. Persistence.xml files contain one for each of the 2 datasources. Explain why and how supposed to be configured?