SURVIVAL STRATEGIES OF STEM FRAGMENTS IN NARROW ENDEMIC AND WIDESPREAD PLANTS OF THE AQUATIC GENUS MYRIOPHYLLUM

For some aquatic macrophytes, stem fragment formed by disturbance plays a key role in the dispersal and establishment of the species. Previous studies have been focused on the regeneration abilities of sterm fragments of a range of aquatic species. However, the information on regeneration ability of fragments between narrow endemic and its congeneric widespread species is lacking. Our study examined the combined effects of fragment length and fragment location on regeneration performances of narrow endemic (Myriophyllum oguraense Miki subsp. yangtzense Wang) and widespread (M. spicatum L.) species, two submerged macrophytes in shallow lakes of the lower Yangtze River basin of China, by an outdoor experiment. Stem fragments from one genotype of population were planted separately in plastic pots by three fragment lengths (5 cm, 10 cm and 15 cm) and three fragment locations (apex, midstem and bottom). The objective of this study were to determine (1) whether fragment length and location correlate with the growth and regeneration abilities of the studied species, and (2) whether the growth and regeneration abilities of fragments differ between the narrow endemic and its congenetic widespread species. The results showed that total plant biomass, total branch biomass and branch number increased significantly with increasing fragment length between all treatments at the fragment level for both species. Total plant biomass, total branch biomass and branch number were greatly different between three length treatments, which were the greatest for fragments of 15 cm in length compared with the other two fragment length treatments. Additionally, the growth and regeneration performance of the studied species were significantly affected by fragment location. There were remarkable differences between the growth of sterm fragments with apices and those without apices. Plant from apical fragments had the largest plant biomass, and midstem fragments regenerated the largest branch biomass, the most lateral branches and the longest branches. Fragments without apices showed significant greater branch number and branch biomass compared with the ones with apices, except that those traits of bottom fragments were intermediate. Meanwhile, plant biomass, branch biomass, branch number, average branch length and branch position inserted at the stem were found to be significantly different between the species studied. For M. oguraense Miki subsp. yangtzense Wang, fragments regenerated larger branch biomass, more lateral branches and longer branches, while fragments produced larger total plant biomass for M. spicatum L., indicating that different regenerative strategies of fragments occurred between the two species. Moreover, apical fragment of M. spicatum L. regenerated lateral branches at the bottom of the stem, while all fragments of M. oguraense Miki subsp. yangtzense Wang produced lateral branches at the top of stem. The present data confirmed the previous conclusion that larger fragments had higher regeneration abilities than smaller fragments and the regeneration potential of fragments with an apical tip was greater than fragments without an apical tip. Our study implied that the regrowth patterns differ between the studied species. M. spicatum L. was prone to increase investment in plant biomass while M. oguraense Miki subsp. yangtzense Wang was prone to invest more to reproduction of lateral branches. This suggested that regeneration performances of fragments of the studied macrophytes were species-specific and fragment trait-dependent, and the results might provide reference for biodiversity conservation and wetland vegetation management.