From Wikipedia about "Citizens United v. FEC": "the First Amendment prohibits government from placing limits on independent spending for political purposes by corporations and unions."

The German system does not place rules on independent spending; it only requires TV channels to provide ad space for political parties that run for office. The amount of space is tied to the relevance of the party, usually measured by the success in the previous election. The TV channel can charge the party 35% of the usual price, this is considered to be the cost price of the channel. [1]

Parties are, of course, allowded to buy additional space, but they would have to pay the usual price. In other words, the German law doesn't limit independent spending.

[1] http://wiki.piratenpartei.de/Grundlagen_f%C3%BCr_Wahlwerbung...