Difference in capacity of clonal integration between terrestrial and aquatic Alternanthera philoxeroides in response to defoliation: implications for biological control

Clonal integration can contribute to the invasiveness of amphibious plant, Alternanthera philoxeroides, but whether this differs between life-forms and whether such difference is underlying their biological control efficacy have scarcely been addressed. We aimed to determine whether clonal integration differs between life-forms and whether terrestrial form with lower biological control efficacy shows greater capacity of clonal integration in response to defoliation. In a greenhouse experiment, we subjected terrestrial and aquatic A. philoxeroides to four levels of experimental defoliation, i.e., 0 (control), 20% (mild), 50% (moderate), and 80% (heavy) leaf clipping, with the stolon connections being either severed or intact. The results showed that clonal integration greatly improved the growth and clonal propagation of both life-forms, especially under heavier defoliation. The shoot/root ratios of both life-forms were significantly increased by clonal integration under heavy defoliation. Moreover, higher level of resource sharing and greater division of labor promoted the terrestrial form to perform better than the aquatic form. These results supported our hypotheses that terrestrial A. philoxeroides can benefit from clonal integration more than aquatic form under herbivory, which may be an alternative mechanism accounted for the low efficacy of biological control of A. philoxeroides in the terrestrial habitats.