Variation of growth and functional traits of invasive knotweeds (Fallopia spp.) in Belgium

Abstract

Three invasive Fallopia taxa are present in Belgium: F. japonica (FJ), F. sachalinensis (FS) and their hybrid F. 9 bohemica (FB). FS is the least invasive of the three taxa. In this study, we compared the taxa, in sites where they co-occur, for differences in functional traits that might influence their competitive ability and invasiveness-shoot height and ramification, leaf size, specific leaf area (SLA) and foliar nitrogen (N) concentration. The three taxa exhibited similar growth kinetics and similar SLA. However, FS differed in its architecture and allocation of leaf area, having less ramified shoots and a steeper gradient of decreasing leaf size along the main shoot. Also, FS had greater foliar N and less efficient N resorption from senescing leaves. These traits values may result in lower competitive ability of FS for light and nitrogen. For the same traits, FB was generally intermediate between FS and FJ, but often closer to the latter. FB was more variable than FS and FJ, possibly due to larger genetic variation. SLA and ramification varied greatly amongst sites for all taxa, due in part to plastic response to contrasting light regimes. Variation in functional traits values may in part explain the variation in invasiveness amongst the members of the Fallopia complex in Belgium.

The influence of invasive Fallopia taxa on resident plant species in two river valleys (southern Poland)

“…In contradiction to other studies (e.g. [36,37]), where selected sites were more variable, the results revealed that sites located along the two rivers hardly differed in the studied soil parameters. Thus, it can be inferred that the sites did not affect the results, and permitted analyses across the two rivers.…”

“…With reference to the above, it can be stated that F. japonica is the most tolerant to high nitrogen variation in soil when compared to the remaining knotweed species. Concerning organic carbon, in our study soils were not very rich, as in the Belgium sites [36], but ours were more similar to the results obtained by Rahmonov et al [45] for F. japonica. Furthermore, the concentration of phosphorus in our soils was very variable as in sites in Belgium [36].…”

“…Concerning organic carbon, in our study soils were not very rich, as in the Belgium sites [36], but ours were more similar to the results obtained by Rahmonov et al [45] for F. japonica. Furthermore, the concentration of phosphorus in our soils was very variable as in sites in Belgium [36]. The significance of the differences in plots scores (CCA) between the three types of plots showed not only slight differences in environmental requirements by knotweeds but, most of all, differences in the biotopic requirements of co-occurring plant species.…”

“…In our study it was revealed that pH in soils in the river valleys were estimated at ca. 6.5., whereas in wasteland in Belgium it varied between 4.9 to 7.4 [36]. Also Rahmonov et al [45] showed that sites invaded by F. japonica are very diverse in pH, from 4.0 to 7.5.…”

“…As regards nitrogen, in our study we focused on nitrate and ammonium ions, which are the available forms of this chemical element for plants, whereas in the majority of studies (e.g. [36,45]) total nitrogen was analyzed and did not exhibit differences among sites [45]. Sites with a higher content of the two forms of available nitrogen were more associated with F. ×bohemica and, most of all, with F. sachalinensis but not with F. japonica, which partially confirms that the latter species can exist in areas with low available nitrogen [16].…”