Colonisation by fragments in six common aquatic macrophyte species

Abstract

Vegetative reproduction is the most common form of propagation in aquatic macrophytes. Fragmentation and consecutive re-rooting of the fragments is one way in which new macrophyte colonies may establish. The success and frequency of this strategy depends on the species and the environment. This study tested how well six species are capable of colonising this way. Tested species are five of the most abundant species of Lake Balaton, where macrophyte recolonisation is still to take place after improving water quality and one potentially invasive species. Fragments of standardized length were examined for survival, rooting rates and length growth during five to six week experiments under laboratory conditions. Effects of species, shoot part (apical or mid-stem part) and seasonality on rooting probability were analysed with logistic regression. Effects on life-cycle were also examined, in terms of continuation of growth and of flowering or seed-set. Species differed significantly in rooting rates and growth, but not in survival rates. Egeria densa, Myriophyllum spicatum and Potamogeton perfoliatus showed the best colonisation properties (survival rates: 95 %, 84 % and 84 %; rooting rates: 88 %, 45 % and 65 %, respectively), while Potamogeton pectinatus colonised less successfully (survival rate: 91 %, rooting rate: 38 %). The annual Najas marina was the only species which frequently reached flowering (61 %), while fragmenting further, without much rooting (rooting rate: 5 %). The non-rooting Ceratophyllum demersum was least impacted by fragmentation and continued growth best, with survival rates of 100 %. Shoot part had a significant influence on rooting rate and length growth. Apical fragments had higher rooting rates and greater length growth than stem fragments, probably due to the action of their meristematic tissue. Differences in the three repetitions of the experiment may be attributable to seasonal changes in colonisation features. It is concluded that recolonisation by fragments might be an effective way for macrophyte populations to recover in Lake Balaton.

Effects of water nutrients on regeneration capacity of submerged aquatic plant fragments

“…The lower regeneration capacities were possible at least partly caused by the exclusion of fragments with apical buds from our experiment, which are known for their high regenerative capacity (Riis et al, 2009;Vari, 2013). As the present study was carried out during summer, it can be ruled out that seasonal effects played a role (Vari, 2013). The average regeneration time was 2-3 weeks in this study, which is similar to the rooting times reported for other submerged species (Vari, 2013).…”

“…As the present study was carried out during summer, it can be ruled out that seasonal effects played a role (Vari, 2013). The average regeneration time was 2-3 weeks in this study, which is similar to the rooting times reported for other submerged species (Vari, 2013). Elodea canadensis and E. nuttallii showed the shortest regeneration time, which might influence the establishment rate of produced plant fragments.…”

“…Even though the regeneration capacities here were lower than in some prior studies with sediment (Langeland and Sutton, 1980;Barrat-Segretain and Cellot, 2007), regeneration capacities of up to > 80% were found. The lower regeneration capacities were possible at least partly caused by the exclusion of fragments with apical buds from our experiment, which are known for their high regenerative capacity (Riis et al, 2009;Vari, 2013). As the present study was carried out during summer, it can be ruled out that seasonal effects played a role (Vari, 2013).…”

“…For successful colonization, the production of new roots is a key factor (Vari, 2013). Interestingly, in four of the tested species here (M. spicatum, M. aquaticum, H. verticillata and C. demersum), regeneration started mostly by the production of new shoots, whereas in E. canadensis, E. nuttallii, E. najas and M. heterophyllum, predominantly a concurrent growth of new shoots and roots was documented right from the beginning of plant regeneration.…”

Environmental opportunities and constraints in the reproduction and dispersal of aquatic plants

“…The high frequency of asexual reproduction in aquatic plants, especially the wide occurrence of shoot fragments as a major way of dispersal (e.g. Vari, 2013), conceals the normally clear distinction between growth and reproduction in land plants.…”