Effects of Orientation on Survival and Growth of Small Fragments of the Invasive, Clonal Plant Alternanthera philoxeroides

BACKGROUND: The ability of small clonal fragments to establish and grow after disturbance is an important ecological advantage of clonal growth in plants and a major factor in the invasiveness of some introduced, clonal species. We hypothesized that orientation in the horizontal position (typical for stoloniferous plants) can increase the survival and growth of dispersed clonal fragments, and that this effect of orientation can be stronger when fragments are smaller and thus have fewer reserves to support initial growth. METHODOLOGY/PRINCIPAL FINDINGS: To test these hypotheses, we compared performance of single-node pieces of stolon fragments of Alternanthera philoxeroides planted at angles of 0, 45 or 90° away from the horizontal position, with either the distal or the proximal end of the fragment up and with either 1 or 3 cm of stolon left attached both distal and proximal to the ramet. As expected, survival and growth were greatest when fragments were positioned horizontally. Contrary to expectations, some of these effects of orientation were stronger when attached stolons were longer. Orientation had smaller effects than stolon length on the performance of fragments; survival of fragments was about 60% with shorter stolons and 90% with longer stolons. CONCLUSIONS/SIGNIFICANCE: Results supported the hypothesis that orientation can affect establishment of small clonal fragments, suggested that effects of orientation can be stronger in larger rather than smaller fragments, and indicated that orientation may have less effect on establishment than amount of stored resources.