When I planted my P Areosulcata alata, it had some wrapped roots, but nothing horrible. I didnt loosen the root ball, just plnted it. It put out 13 culms within a month of planting it, and these were slightly smaller then the existing culmts. This has happened to every bamboo I plant. I dont losen the roots, I just plant it. They shoot pretty well, and they all generally had culms slightly smaller then the existing culms.
The only bamboo I planted (OUt of , F Rufa and F Scabrida, P Areosulcata, and Pseudosasa Japonica), that put out larger culms, was the Fargesia Scabrida. The thing did not stop shooting until the first really heavy frost. I killed it with poor protection/wrong plant