You can reach Merano by bike thanks to the wonderful cycle path that runs thourgh the apple plantages and along the river Adige/Etsch. The tour also pass by Castle Firmiano/Sigmundskron, Terlano and Gargazzone. After Postal/Burgstall you will reach sinigo/Sinich and then Merano.
If you rent your bike at the “Südtirol Rad” rental point in Bolzano, you may give it back at that company’s rental point in Merano so you can return by train to Bolzano. For the latter option, you may want to purchase the Bikemobil Card, which combines two different offers: unlimited travelling on all of South Tyrol’s means of public transport and a day trip on a borrowed bicycle.
If you ride your own bicycle you can bring it with you on the train. The daily ticket for the bike costs € 7.