Study On The Growth And Propagation Strategies Of An Aquatic Species Myriophyllum Oguraense Subsp. Yangtzense

Regeneration is very important for the growth and maintenance of plant population in the life history. Regeneration or propagation strategies differ from the species under environmental pressures. Many researches have been done on the ecological adaptability of growth pattern and regeneration mechanism in plant population at present. Myriophyllum oguraense subsp. yangtzense, a submerged macrophyte, is confined to the lower Yangtze River valley of China. The species relies heavily on turions and plant fragments for regeneration. Since plant vegetative fragments cannot over winter and seed propagation is very rare, turions serve the functions of overwintering structures to survive the severe conditions. Few studies have focused on the growth and propagation of this endemic species. Therefore, it is crucial to understand the factors affecting the spread of population to an unoccupied area and the likelihood for establishment of immature plants.In the present study, we firstly investigated effects of turion size and water depth on the submerged macrophyte M. oguraense subsp. yangtzense when grown in outdoor ponds, in order to determine the underlying factors affecting its persistence (sprouting) at early life-history stages. Secondly, we tested whether turion germination differs by size of turions and how the combined effects of turion size and cold treatment affect turion germination of M. oguraense subsp. yangtzense. Thirdly, we studied the possible adaptive mechanisms of M. oguraense subsp. yangtzense to water fluctuation including the depth, duration and frequency of inundation. Finally, regeneration performances of narrow endemic (M. oguraense subsp. yangtzense) and widespread (M. spicatum) plants in the aquatic genus Myriophyllum were investigated by coupling of stem fragment length (5 cm,10 cm,15 cm) and fragment location (apex, midstem, bottom).The purpose of this study was to evaluate plant establishment and propagation ability of M. oguraense subsp. yangtzense under some biotical and environmental factors. The results are mainly as follows:1. Turion size significantly affected the development of adventitious roots and elongation of the newly emerged axis. Root development occurred earliest in large turions and latest in small turions, while axis elongation occurred earliest in small turions and latest in large turions. Additionally, turion size showed significant effect on the percent emergence, total plant biomass and plant height, which all significantly increased with the increasing turion size. Turion size and turion size×water depth interaction also significantly affected the emergence time, which delayed with the decreasing turion size.2. Fragment size significantly affected the growth and regeneration of the studied species. Total plant biomass, total branch biomass and branch number increased significantly with increasing fragments length. In addition, fragment location showed significant effect on the growth and regeneration of the studied specie. Plant from apical fragments had largest plant biomass, and midstem fragments regenerated largest branch biomass, most lateral branches and longest branches.3. Water depth significantly affected the mean number of days to first immature plant emergence. Water depth×turion size interaction also significantly affected the emergence time. The increasing water depth delayed significantly the plant emergence of both small and large turions in shallower water treatments (0 cm and 20 cm). Small and large turions’ responses differed significantly at each water depth except for 40 cm. Additionally, water depth showed no significant effect on percent emergence. Plant emergence was highest at 0 cm water depth, and increased with increasing turion size at each water depth except for 40 cm.4. After the cold treatment, the time required for new axis emergence of turions was remarkably shortened and variation among the three turion sizes was greatly diminished. In addition, the interaction of cold treatment×turion size significantly affected the mean number of days required for both root and axis emergence. With cold treatment time increasing, the time required for axis emergence was reduced among the three turion sizes, and there was an obvious temperature-dependent effect of turion size on root development.5. The inundation had significant negative effects on plant biomass and the production of new branches. Total plant biomass and the number of new branches reduced as the water depth and duration increased. More branches were produced as the frequency of inundation increased. Additionally, inundation had positive effects on plant height and stem mass ratio. As water depth and frequency increased, plant height decreased significantly while branch mass ratio increased.6. Plant biomass, branch biomass, branch number, average branch length, and position of branch were significantly different between two species. Fragments of M. oguraense subsp. yangtzense regenerated larger branch biomass, more lateral branches and longer branches, while those of M. spicatum produced larger total plant biomass. Moreover, apical fragment of M. spicatum regenerated lateral branches at the bottom of the stem, while all fragments of M. oguraense subsp. yangtzense produced lateral branches at the top of stem, indicating that different regenerative strategies of fragments occurred between the studied species.Our results indicate that large turions and shallow water favor the early establishment and early life-history trade-offs in allocation influence immature plant survival. Allocation to sprouting appears to enhance the ability of immature plants to survive unfavorable conditions. In addition, turion size and temperature combined are determinants for the germination process, which in turn influence the vegetative regeneration of M. oguraense subsp. yangtzense. Moreover, regeneration performances of fragments are species specific and dependent on fragment traits, providing data for biodiversity conservation and wetland vegetation management. We proposed that different responses of turions and fragments play an important role in influencing the abundance and distribution of this endemic population. The study can assist in predicting vegetation response to water fluctuation in natural and modified wetlands and provide data for biodiversity conservation and wetland vegetation management.