Experimental study of vegetative regeneration in four invasive Reynoutria taxa (Polygonaceae)

Garden experiments focused on vegetative regeneration were carried out with four invasive taxa of the genus Reynoutria (R. japonica var. japonica, R. japonica var. compacta, R. sachalinensis and a hybrid between R. sachalinensis and R. japonica var. japonica, R. x bohemica). Regeneration ability of stems and rhizomes, timing of shoot emergence and biomass production were studied under the following treatments: laid horizontally on the soil surface; placed upright; buried in the soil; floating in water. Two different soils (sand and garden loam) representing contrasting nutrient levels were applied. Differences were found in the capability and speed of regeneration, as well as in the quality of shoots produced. Regeneration from stems was less efficient than that from rhizomes in all taxa except R. sachalinensis. R. x bohemica exhibits higher regeneration potential (61%) than all other taxa and can be considered as the most successful taxon of the Czech representatives of the genus Reynoutria in terms of regeneration and establishment of new shoots. High regeneration capacity was also exhibited by R. japonica var. compacta (52%). Other taxa showed generally lower regeneration rates (R. japonica var. japonica 39% and R. sachalinensis 21%), but under some treatments the percentage of regenerated segments was high, too. R. japonica var. japonica rhizomes regenerated successfully in all three soil treatments but not in the water. An opposite pattern was found for its stems: they regenerated well if exposed to water treatment but in the soil, they did not regenerate at all. Particular taxa responded to the soil type in a contrasting way. R. sachalinensis and R. x bohemica regenerated better in loam while the opposite was true in R. japonica var. japonica. R. japonica var. compacta produced the tallest and R. x bohemica the heaviest and most robust shoots. It is concluded that rhizomes are more crucial than stems for the spread of knotweeds through fragmentation and clonal growth, suggesting the importance of soil disturbance.