Expansion pathways of the exotic common reed (Phragmites australis): a historical and genetic analysis

Using 779 herbarium and modern specimens, we reconstructed the spread of the common reed ( Phragmites australis ) in Quebec, Canada, where large-scale invasion of this plant species has been reported since the 1960s. All specimens were genetically differentiated using molecular tools to identify the genotype (native or exotic). The exotic genotype (haplotype M) has been present in Quebec as early as 1916, but it was rare prior to the 1970s and was almost exclusively restricted to the shores of the St. Lawrence River. The exotic genotype spread inland only after the beginning of the 1970s. In less than 20 years, a complete shift occurred, from the dominance of native genotypes to the dominance of the exotic genotype. Today, more than 95% of common reed colonies found in Quebec are dominated by the haplotype M. It is especially abundant along roads, but colonies present in marshes are also dominated by the exotic genotype. This study provides evidence that, in Quebec, the development of the highway network in the 1960s and 1970s strongly contributed to the inland expansion of the exotic genotype. Moreover, it shows the usefulness of molecular techniques for reconstructing the spread of an invader. Without the use of molecular tools, the reconstruction of invasions of exotic taxa would be impossible because of the lack of clear phenotypic differences between genotypes.     

Microcystin-LR, a cyanobacterial toxin, induces growth inhibition and histological alterations in common reed (Phragmites australis) plants regenerated from embryogenic calli

The aim of this study was to establish the histological effects of exposure to microcystin-LR (MC-LR), a cyanotoxin, on axenic Phragmites australis plantlets. Plantlets were regenerated from embryogenic reed calli by tissue culture methods. Microcystin-LR inhibited the growth and development of embryogenic calli and the growth of reed plantlets. The 50% plantlet growth inhibitory concentration value (IC50) of MC-LR was 12 microg ml(-1) (12.07 microM) on mineral medium and 36 microg ml(-1) (36.22 microM) on Murashige-Skoog medium. In the case of roots, the IC50 value was 4.1 microg ml(-1) (4.12 microM) on both media. Microcystin-LR induced aerenchyma obturation, altered lignification of cell walls in the axial organs, root necrosis and the capture of lateral or adventitious roots in the tissues of axial organs of reed plantlets. Cyanotoxin induced the premature development of lateral roots, root coalescence and early aerenchyma formation. Our data suggest that microcystin-LR, a cyanotoxin, induced developmental and histological alterations leading to growth inhibition of reed, and the induced harms have an impact on understanding reed decay in eutrophic fresh waters.     

Effects of external iron concentration upon seedling growth and uptake of Fe and phosphate by the common reed, Phragmites australis (Cav.) Trin ex. Steudel

The objectives of this study were to determine whether, and to what degree, the aqueous iron concentration in the growing medium affects the growth of, and Fe uptake by, Phragmites australis, and whether the presence of iron in the growing environment affects the uptake of the essential element phosphate. The wetland macrophyte P. australis was grown under laboratory conditions in nutrient solution (0.31 mg L(-1) phosphate) containing a range of iron concentrations (0-50 mg L(-1) Fe). A threshold of iron concentration (1 mg L(-1)) was found, above which growth of P. australis was significantly inhibited. No direct causal relationship between iron content in aerial tissues and growth inhibition was found, which strongly suggests that iron toxicity cannot explain these results. Phosphate concentrations in aerial tissues were consistently sufficient for growth and development (2-3 % d. wt) despite significant variation in concentration of phosphate associated with roots. External Fe concentration had a significant effect on the growth of P. australis and on both Fe and phosphate concentrations associated with roots. However, neither direct toxicity nor phosphate deficiency could explain the reduction in growth above 1 mg L(-1) external Fe concentration     

Flow cytometric assessment of cytotype distributions within local populations of Phragmites australis (Poaceae) around Lake Biwa,the largest lake in Japan

Phragmites australis (Poaceae) is a clonal perennial that is an important component of wetland ecosystems worldwide. Using flow cytometry, we examined the cytotype distributions within five populations of P. australis located in the vicinity of Lake Biwa. As in previous reports, two ploidy levels, octoploid (2n = 8x = 96) and decaploid (2n = 10x = 120), were identified, which are assumed to be the main cytotypes around the lake. The coexistence of two cytotypes was detected in four of the five populations, suggesting the relatively common occurrence of mixed ploidy levels in the populations around Lake Biwa. Although intermingled cytotype distributions were observed in some populations, the 9x cytotype, that is, the expected outcome of inter‐cytotype crosses, was not observed, indicating limited gene flow between the two cytotypes.     

Effects of lead contamination on the clonal propagative ability of Phragmites australis (common reed) grown in wet and dry environments

Clonal propagation is important for the survival and maintenance of the common reed Phragmites australis. Pot culture experiments were conducted to investigate the effects of lead (Pb) concentration (0, 500, 1500, 3000, 4500 mg·kg^?1) and water stress on the clonal reproductive ability of this species. The Pb concentration found in plant organs, in decreasing order, was roots >shoots >rhizomes. There was a negative relationship between the growth of clonal propagative modules (excluding axillary shoot buds) and Pb concentrations, which caused a decrease in biomass, rhizome growth and number of axillary and apical rhizome buds. Daughter axillary shoots exhibited a tolerance strategy, with no significant change in their number; the axillary and apical rhizome buds, daughter apical rhizome shoots and rhizomes exhibited compensatory growth during the late stage of Pb (excluding 4500 mg·kg^?1) treatment in a wet environment. Pb applications above 500 mg·kg^?1 reduced these parameters significantly in the drought treatment, except for the number of axillary shoot buds, which did not change. Our results indicate that clonal propagative resistance to Pb contamination can occur via tolerance strategies, compensatory growth and a Pb allocation strategy, enabling these reeds to maintain population stability in wet environments. However, clonal modular growth and reproductive ability were inhibited significantly by the interaction between drought and Pb, which would cause a decline in P. australis populations in a dry environment. Lead concentrations of 4500 and 500 mg·kg^?1 in soils might meet or exceed the Pb tolerance threshold of clonally propagated reeds in wet and dry environments, respectively.