Mechanical control inadvertently increases risk of alien plant invasion: influence of stem fragmentation and inundation regimes on Arundo donax regeneration in Neotropical savanna

Context. Arundo donax L. is an exotic, perennial grass that has invaded dryland and wetland savannas of central Brazil. This species produces sterile flowers in its introduced range and propagates vegetatively via rhizomes and stem fragments. Aims. We investigated bud sprouting capacity after fragmentation, which plays a major role in plant-proliferation ability, invasiveness and its escape from weed-control measures. Methods. We evaluated the effects of size, different periods of desiccation (by exposure to air), submersion and water-column height on the regenerative capacity of single-node stem fragments. Key results. Fragments of a minimum size of 3-4 cm successfully regenerated new plants. The regenerative capacity of single-node stem fragments (3-10 cm length) rapidly decreased after 1 week of air desiccation. Stem fragments that were submerged for 30 days resprouted and formed plants in a water column of 5, 10 or 15 cm, with no significant difference from the controls. However, leaves did not expand and shoot elongation was adversely affected in 15 cm of non-aerated water. This loss of performance was reversed when the newly formed plants were removed from the water and transferred to a moist substrate. Implications. Our findings suggest that weed management, which involves cutting the plant to ground level without removing it from the site, is inefficient and can intensify the potential for invasion by A. donax, especially in the rainy season, when left-over stem fragments remain hydrated and capable of regeneration. Its establishment near riverbanks must be monitored because submerged propagules remain viable and able to resprout.