Techniques are described for wavelength and spectrum assignment within a packet-optical transport system. A controller, for example, dynamically controls wavelength and spectrum assignment to suppress or generally avoid optical effects that can degrade communication performance. For example, the controller provides closed-loop control over dynamic partitioning of the spectral range of an optical transport system into channel groups and assignment of the groups to respective packet-optical transport devices based on current or future bandwidth requirements at each device. Moreover, for each packet-optical transport device, the controller controls assignment of individual wavelengths within each channel group so as to balance channel utilization around a center of the spectral range associated with each channel group and to maintain spectral separation of the channels within the channel group.