Comparison of dispersal capacity via fragmentation of submerged aquatic invasive alien plants in New Zealand
In general, in most submerged alien invasive plants (for example Elodea canadensis and other Hydrocharitaceae) seed production is absent due to the presence of only one gender in the introduced range. Thus, the spread of these species is restricted to the dispersal of asexual propagules where stem fragments are one of the most common dispersal units for such submerged aquatic plants. The potential stem fragmentation of three invasive alien plants to New Zealand (E. canadensis, Egeria densa (EPPO List of Invasive Alien Plants) Lagarosiphon major) was evaluated under different flow velocities and two different light conditions in a large flow tank. Plants were field collected and 100 apical shoots (25 cm in length) were separately planted in 8 trays for each species. For each species two trays were transferred to the flow tank for a period of 8 days when the plant shoots were between 40 – 60 cm in length at the beginning of the experiment. Prior to the start of the experiment, plants were maintained for three days in the flow tank with a water velocity of 0.05 m s -1 where all plants were exposed to low light conditions using an 80 % shade cloth. For high light conditions a 50 % shade cloth was used. Following three days of acclimation, flow velocity was increased by 0.1 m s -1 from 0.1 m s -1 to 0.4 m s -1 every two days. A 15 mm mesh was positioned downstream of the plants to collect fragments. In total, 213 fragments were produced by 2 400 plant shoots with E. canadensis showing higher fragmentation rates than E. densa and L. major. Light intensity had no effect on the number of fragments produced. E. canadensis produced the longest fragments (9.8 ± 0.7 cm) followed by E. densa (7.3 ± 0.8 cm) then L. major (3.2 ± 1.1cm). There was no effect of velocity on fragment length. The plant fragments produced during the experiment were tested for their reproductive capacity with E. canadensis exhibited the highest regeneration with 92 % of all fragments regenerating within four weeks. For E. densa, 88 % of fragments regenerated and L. major 50 % regeneration was observed. These data are important information to gather for the species in order to assess their risk potential and the likelihood of unintended spread.
Sources
Redekop P, Hofstra D, Hussner A (2016) Elodea canadensis shows a higher dispersal capacity via fragmentation than Egeria densa and Lagarosiphon major. Aquatic Botany 130, 45-49.