Abstract
As ecosystem engineers, invasive earthworms are one of the main drivers of plant community changes in North American forests previously devoid of earthworms. One explanation for these community changes is the effects of earthworms on the reproduction, recruitment, and development of plant species. However, few studies have investigated functional trait responses of native plants to earthworm invasion to explain the mechanisms underlying community changes. In a mesocosm (Ecotron) experiment, we set up a plant community composed of two herb and two grass species commonly found in northern North American forests under two earthworm treatments (presence vs. absence). We measured earthworm effects on above- and belowground plant biomass and functional traits after 3 months of experiment. Our results showed that earthworm presence did not significantly affect plant community biomass and cover. Furthermore, only four out of the fifteen above- and belowground traits measured were affected by earthworm presence. While some traits, such as the production of ramets, the carbon and nitrogen content of leaves, responded similarly between and within functional groups in the presence or absence of earthworms, we observed opposite responses for other traits, such as height, specific leaf area, and root length within some functional groups in the presence of earthworms. Plant trait responses were thus species-specific, although the two grass species showed a more pronounced response to earthworm presence with changes in their leaf traits than herb species. Overall, earthworms affected some functional traits related to resource uptake abilities of plants and thus could change plant competition outcomes over time, which could be an explanation of plant community changes observed in invaded ecosystems.
Highlights
Biological invasions are one of the most important threats to native biodiversity (Davis, 2009; Wardle et al, 2011; Díaz et al, 2019)
The species-specific cover and biomass depended on the species identity (Df = 3, χ2 = 53.95, p < 0.0001 and Df = 3, χ2 = 298.04, p < 0.0001, Figures 2A,B, respectively, and Supplementary Material 3), with a higher cover and biomass produced by the species A. millefolium and lower values for S. laeve
Our study provides novel insights into the trait responses of different plant species under earthworm invasion and indicates that these changes of plant strategies are not necessarily mediated by the effects of earthworms on gross soil abiotic properties and on the soil microbial activity or community structure
Summary
Biological invasions are one of the most important threats to native biodiversity (Davis, 2009; Wardle et al, 2011; Díaz et al, 2019). Invasive Earthworms Drive Plant Traits services (Frelich et al, 2012, 2019) These effects are even stronger when recipient ecosystems lack functionally similar native soil fauna (Wardle et al, 2011), such as the case for earthworms in many regions in northern North America. Invasive earthworms influence seed bank composition, seed recruitment, and the development and survival of seedlings (Hopfensperger et al, 2011; Clause et al, 2015; Dobson and Blossey, 2015; Nuzzo et al, 2015; Cassin and Kotanen, 2016) The outcome of these earthworm–seed interactions may depend on the morphological and chemical traits of seeds (Eisenhauer et al, 2009c; Clause et al, 2011, 2017). We lack information about potential changes of a set of plant functional traits to better understand plant responses to exotic earthworm presence, and the mechanisms behind native plant community changes
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