Impacts of an invasive plant on primary production: Testing a functional trait‐based framework with a greenhouse experiment

Abstract

Questions Predicting when invasive species will affect ecosystem functioning remains problematic, with strong contingency upon both the invasive species and the recipient community's identities. Adopting a functional trait‐based approach might overcome this context‐dependence. As an early exploration of this approach, we used a greenhouse experiment with seeds of the invasive plant Impatiens glandulifera to assess the potential invasion effects on community trait composition and biomass production. Location Three distant European seed origins, northern France, southern Sweden and central Norway, into transplanted turves from Trondheim, Norway. Methods At the end of the greenhouse experiment, we measured plant height, specific leaf area (SLA), leaf dry matter content (LDMC) and standing biomass of both the invasive plant and the turf communities. With these data we evaluated invasion effects on community trait composition and standing biomass (as a first test of ecosystem function effects), including dependence on invasive species origin and recipient community composition. Results Invasion by I. glandulifera introduced divergent trait values (high plant height and SLA, low LDMC) to the recipient community. The trait set of both the invader and, to a lesser extent, the community were altered following invasion, seemingly driven by increased light competition. Competitive and graminoid‐dominated communities showed stronger changes in LDMC following invasion. Functional traits of both the communities and the invasive species helped explain the increase in standing biomass. Southern invader plants more strongly affected the recipient community than their northern counterparts, resulting in stronger biomass reduction of the recipient community. Conclusions This study shows how invasion‐induced increases in productivity are effectuated through both the introduction of different invader traits and shifts in the co‐occurring species trait set, illustrating the potential of a functional trait‐based approach.

Optical traits perform equally well as directly‐measured functional traits in explaining the impact of an invasive plant on litter decomposition

“…Interestingly, in our study, the initially observed invader impact on litter decomposition, could seemingly be completely explained by changes in the functional trait set of the native community following invasion (invasion status not retained in the final trait models based on CWM values excluding R. rugosa), rather than by the invader's trait set. These results thus add to the literature that illustrates how invader induced ecosystem impacts can be caused by competition effects on the native community's trait composition, rather than directly by the invader's presence (Aerts et al, 2017;Helsen, Kapás, et al, 2018;Helsen, Smith, et al, 2018).…”

“…These invader impacts on ecosystem functioning are not necessarily directly driven by the introduction of new functional traits by the invader, but can also be mediated by invader-induced changes in the trait spectrum of the native species in the invaded community (Strayer, 2012). Such trait spectrum changes can be effectuated by invasion-induced changes in species composition (Hejda & de Bello, 2013) or by invasion-induced intraspecific changes in the native species' traits, irrespective of species composition changes (Helsen, Kapás, Rakvaag, Speed, & Graae, 2018;Helsen, Smith, et al, 2018). Even in cases where ecosystem function changes are directly driven by the newly introduced traits of the invader, impacts are usually dependent on the functional distinctiveness of the invader in reference to the trait spectrum of the invaded community (Finerty et al, 2016;Kuebbing & Bradford, 2019;Lee et al, 2017;Pyšek et al, 2012;Scharfy, Funk, Olde Venterink, & Güsewell, 2011).…”

Impacts of dominant plant species on trait composition of communities: comparison between the native and invaded ranges

“…This idea is supported by the results of a case study on the invasive herb Impatiens glandulifera , which brought new characteristics into the invaded community, such as tall stature, high SLA, and a low leaf dry matter content (LDMC; Helsen et al. ). On the other hand, Funk et al.…”

“…Recently, Div ı sek et al (2018) showed that this depends on the invasion stage-naturalized species in central European habitats tend to be similar in their functional traits to native members of the community, while to become invasive, the species need to possess different traits. This idea is supported by the results of a case study on the invasive herb Impatiens glandulifera, which brought new characteristics into the invaded community, such as tall stature, high SLA, and a low leaf dry matter content (LDMC; Helsen et al 2018). On the other hand, Funk et al (2016) demonstrated that invaders in the Mediterranean region tend to be similar to native species in terms of their life-form.…”

Inter‐ and intraspecific trait variation shape multidimensional trait overlap between two plant invaders and the invaded communities

“…Also invader impact on community composition and ecosystem functioning has been hypothesized to depend on the functional distinctiveness of the invader compared to the trait spectrum of the local invaded community (Ehrenfeld 2010, Wardle et al 2011, Drenovsky et al 2012. For several invasive plant species, the invader's distinctiveness in specific traits has been found to be proportional to its impact on ecosystem functions such as biomass production and litter decomposition (Scharfy et al 2011, Finerty et al 2016, Helsen et al 2018a.…”