Impacts of alien invasive plants on soil nutrients are correlated with initial site conditions in NW Europe

Abstract

Alien invasive plants are capable of modifying ecosystem function. However, it is difficult to make generalisations because impacts often appear to be species-and site-specific. In this study, we examined the impacts of seven highly invasive plant species in NW Europe (Fallopia japonica, Heracleum mantegazzianum, Impatiens glandulifera, Prunus serotina, Rosa rugosa, Senecio inaequidens, Solidago gigantea) on nutrient pools in the topsoil and the standing biomass. We tested if the impacts follow predictable patterns, across species and sites or, alternatively, if they are entirely idiosyncratic. To that end, we compared invaded and adjacent uninvaded plots in a total of 36 sites with widely divergent soil chemistry and vegetation composition. For all species, invaded plots had increased aboveground biomass and nutrient stocks in standing biomass compared to uninvaded vegetation. This suggests that enhanced nutrient uptake may be a key trait of highly invasive plant species. The magnitude and direction of the impact on topsoil chemical properties were strongly site-specific. A striking inding is that the direction of change in soil properties followed a predictable pattern. Thus, strong positive impacts (higher topsoil nutrient concentrations in invaded plots compared to uninvaded ones) were most often found in sites with initially low nutrient concentrations in the topsoil, while negative impacts were generally found under the opposite conditions. This pattern was significant for potassium, magnesium, phosphorus, manganese and nitrogen. The particular site-specific pattern in the impacts that we observed provides the first evidence that alien invasive species may contribute to a homogenisation of soil conditions in invaded landscapes.

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

“…Our results agree with those of Scharfy et al (2009Scharfy et al ( , 2010 and Quist et al (2014) who found that S. gigantea invasion had no influence or decreased soil respiration, bacterial biomass, or phosphomonoesterase activity but increased fungal biomass and/or fungal:bacterial ratio. S. gigantea litter may support fungal rather than bacterial growth as it has lower tissue concentrations of most nutrients and higher C:N ratio than adjacent native vegetation Thorn and Lynch 2007;Dassonville et al 2008). However, such differences in tissue nutrient concentrations were not found by other authors (Stefanowicz et al unpublished).…”

“…Presumably the influence of fluvial processes we had expected in the river floodplain was too weak to alter soil properties as well as plant species richness and cover considerably. Dassonville et al (2008) and Scharfy et al (2009) found that the direction and magnitude of changes in soil properties induced by invasion differed between study sites, but their sites showed differences in initial (preinvasive) soil properties. Specifically, invasion increased nutrient concentrations of surface soils with initially low nutrient concentrations, while under the opposite conditions a negative impact was mainly observed (Dassonville et al 2008).…”

“…Invasive plants are often characterized by higher productivity than co-occurring native vegetation (Vilà et al 2011;Jo et al 2015). The biomass produced by R. japonica is 2-5 times greater and characterized by lower concentrations of essential nutrients such as N, P, K, Mg, or Mn than the biomass of native plants (Dassonville et al 2008;Aguilera et al 2010). Moreover, the tissues of R. japonica are characterized by relatively high C:N and lignin:N ratios at the time of senescence and litterfall (Aguilera et al 2010;Mincheva et al 2014).…”

“…Dassonville et al (2008) reported that invasion increased nutrient concentrations of surface soils with initially low nutrient concentrations, while under the opposite conditions, a negative impact was mainly observed. Similarly, Scharfy et al (2009) discovered that the effects of invasion on some soil physicochemical properties depended on P availability, being more pronounced at more P-rich sites.…”

“…The magnitude and direction of changes in soil characteristics and processes brought about by invasion depend on local habitat conditions, invasive plant species traits, and/or the interaction of both (Meyerson et al 2000;Ehrenfeld 2003;Koutika et al 2007;Dassonville et al 2008;Scharfy et al 2009;Vilà et al 2011;Hulme et al 2013;Castro-Díez et al 2014). Dassonville et al (2008) reported that invasion increased nutrient concentrations of surface soils with initially low nutrient concentrations, while under the opposite conditions, a negative impact was mainly observed.…”