Assessment of Aboveground and Belowground Vegetative Fragments as Propagules in the Bioenergy Crops Arundo donax and Miscanthus × giganteus

Giant miscanthus (Miscanthus × giganteus) and giant reed (Arundo donax) are leading bioenergy crops. Both exhibit many invasive characteristics, though only giant reed is known to be invasive. Despite this, neither produces viable seed, limiting movement to vegetative propagules. Therefore, to assess vegetative fragments as potential propagules, we quantified seasonal changes in culm node viability and performance in giant miscanthus and giant reed under greenhouse conditions. Giant miscanthus culms were collected in spring, summer, fall, and winter from established fields, while giant reed culms were collected in summer, fall, and winter from feral stands. Treatments at each timing consisted of whole culms and single-node culm fragments planted in soil or placed in standing water for an 8-week period. Giant miscanthus whole culms and fragments produced shoots and roots in both soil and standing water immediately following cutting from spring to summer, but failed to produce shoots and roots after fall and winter cutting dates. All rhizome fragments survived and generated shoots and roots after burial. By comparison, giant reed produced shoots and roots in both soil and standing water throughout the year, regardless of cutting date. With giant miscanthus, precautions should be taken when living culms or rhizome fragments are harvested and transported through riparian habitats during the summer months. By comparison, giant reed showed a remarkable increase in propagule generation and productivity throughout the year and, thus, escaped propagules present a far greater risk of unintentional establishment compared to giant miscanthus.