Does the invasive species Reynoutria japonica have an impact on soil and flora in urban wastelands?

Abstract

International audienceInvasive plants are recognised as a major threat to biodiversity. Although they are well-established in natural areas, the supposed negative impacts of invasive plants upon communities and ecosystems have so far been poorly investigated in urban areas, where invasions are a main issue for ecologists and for urban planners and managers. We propose to assess the effects of an invasive species along an invasion gradient in a typical urban habitat. We focused on the Japanese knotweed (Reynoutria japonica Houtt.), a widespread invasive species in Europe and North America. We considered eight urban wastelands invaded by this species in the heart of the Greater Paris Area, France. On each site, we ran four transects from the centre of the Japanese knotweed patch towards the uninvaded peripheral vegetation. We recorded the flora using the line intercept method, and several soil parameters (thickness of A horizon, abundance of earthworm casts, topsoil Munsell value, pH) every metre along each transect. The A horizon was thicker and the topsoil darker under R. japonica canopy. Thus, this invasive plant species seemed to influence soil organic matter pool. However, our results also steadily showed that R. japonica locally excluded and/or severely reduced the cover of many plant species through competition. Our study clarified the local effects of R. japonica: an influence on the soil organic matter, and a severe negative impact on wasteland plant communities. We suggest implications in both conservation and restoration ecology

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

“…In different types of habitats i.e. urban wastelands in 40 transects a total of 83 species were found [52]. This is a probably consequence of the relatively long residence time of knotweeds in the sites studied in the present investigation.…”

“…As far as the resident species is concerned, some studies have shown that one of the most frequent accompanying species to Fallopia spp. is Urtica dioica [16,20,22,52]. It is a nitrophilous species, typical for riparian habitats.…”

Differential influence of four invasive plant species on soil physicochemical properties in a pot experiment

“…Large quantities of senescent plant biomass reach the soil surface during litterfall and undecomposed litter fragments may accumulate in the form of a thick layer if the litter quality, and hence, its decomposition rate are low. Such a phenomenon was observed in R. japonica, contributing to changes in both soil properties and plant communities (Maurel et al 2010;Stefanowicz et al 2016;Stefanowicz et al 2017). The quality and quantity of plant biomass differ considerably among invasive species.…”

“…Overall, total and available forms of N (N-NO 3 , N-NH 4 ) and P (Olsen), S-SO 4 , exchangeable K, and Mg contributed the most to the discrimination of soils under different plant species. The influence of invasive I. glandulifera, R. japonica, and S. gigantea on soil has been estimated earlier in numerous field studies Vanderhoeven et al 2006;Dassonville et al 2008;Scharfy et al 2009;Maurel et al 2010;Tharayil et al 2013;Quist et al 2014;Ruckli et al 2013Ruckli et al , 2014bStefanowicz et al 2017), but experiments concerning this problem are rare (Scharfy et al 2010(Scharfy et al , 2011Bardon et al 2014Bardon et al , 2016. Previous studies focused mainly on invasion-induced changes in different forms of N and P in soil and found that these properties responded variably to the presence of I. glandulifera, R. japonica, or S. gigantea, and so did some exchangeable cations, for example K and Mg (ChapuisLardy et al 2006;Hejda and Pyšek 2006;Vanderhoeven et al 2006;Dassonville et al 2007;Scharfy et al 2009Scharfy et al , 2010Scharfy et al , 2011Tharayil et al 2013;Ruckli et al 2014b;Stefanowicz et al 2017).…”

Species-specific effects of plant invasions on activity, biomass, and composition of soil microbial communities

“…R. japonica invasion may have actually affected microbial properties through changes in soil chemical characteristics, as it altered the amount of soil N-NO 3¯i n comparison to control soil (Stefanowicz et al unpublished). The poor quality of litter produced by R. japonica and low microbial activity and decomposition rate accumulated large, undecomposed fragments of organic matter and increased the organic layer thickness under the plant (Maurel et al 2010). The thickness of the organic layer reached ca.…”