Abstract
We aim to understand how small-scale genotypic richness and genotypic interactions influence the biomass and potential invasiveness of the invasive grass, Phalaris arundinacea under two different disturbance treatments: intact plots and disturbed plots, where all the native vegetation has been removed. Specifically, we address the following questions (i) Does genotypic richness increase biomass production? (ii) Do genotypic interactions promote or reduce biomass production? (iii) Does the effect of genotypic richness and genotypic interactions differ in different disturbance treatments? Finally (iv) Is phenotypic variation greater as genotypic richness increases? We conducted a 2-year common garden experiment in which we manipulated genotype richness using eight genotypes planted under both intact and disturbed conditions in a wetland in Burlington, Vermont (44°27′23″N, 73°11′29″W). The experiment consisted of a randomized complete block design of three blocks, each containing 20 plots (0.5 m²) per disturbed treatment. We calculated total plot biomass and partitioned the net biodiversity effect into three components: dominance effect, trait-dependent complementarity and trait-independent complementarity. We calculated the phenotypic variance for each different genotype richness treatment under the two disturbance treatments. Our results indicate that local genotypic richness does not increase total biomass production of the invasive grass P. arundinacea in either intact or disturbed treatments. However, genotypic interactions underlying the responses showed very different patterns in response to increasing genotypic richness. In the intact treatment, genotypic interactions resulted in the observed biomass being greater than the predicted biomass from monoculture plots (e.g., overyielding) and this was driven by facilitation. However, facilitation was reduced as genotypic richness increased. In the disturbed treatment, genotypic interactions resulted in underyielding with observed biomass being slightly less than expected from the performance of genotypes in monocultures; however, underyielding was reduced as genotypic richness increased. Thus, in both treatments, higher genotypic richness resulted in plot biomass nearing the additive biomass from individual monocultures. In general, higher genotypic richness buffered populations against interactions that would have reduced biomass and potentially spread. Phenotypic variance also had contrasting patterns in intact and disturbed treatments. In the intact treatment, phenotypic variance was low across all genotypic richness levels, while in the disturbed treatment, phenotypic variance estimates increased as genotypic richness increased. Thus, under the disturbed treatment, plots with higher genotypic richness had a greater potential response to selection. Therefore, limiting the introduction of new genotypes, even if existing genotypes of the invasive species are already present, should be considered a desirable management strategy to limit the invasive behavior of alien species.
Highlights
Species diversity at small scales can have a large influence on ecosystem processes (Barton et al 2015; Hooper et al 2005; Schöb et al 2015; Srivastava and Vellend 2005)
Important Findings Our results indicate that local genotypic richness does not increase total biomass production of the invasive grass P. arundinacea in either intact or disturbed treatments
While high species diversity within communities has been posited to reduce the invasability of a community through biotic resistance (Kennedy et al 2002; Richardson et al 2000; Elton 1958), high genotypic diversity of the introduced species may increase the chance of a successful establishment of a plant species and its invasive potential (Lavergne and Molofsky 2007)
Summary
Species diversity at small scales can have a large influence on ecosystem processes (Barton et al 2015; Hooper et al 2005; Schöb et al 2015; Srivastava and Vellend 2005). Intraspecific plant diversity has been shown to influence plant productivity (Crawford and Rudgers 2012; Crutsinger et al 2006; Dudley and File 2007; Kotowska et al 2010; Schöb et al 2015), resistance to stress (Hughes and Stachowicz 2011; Reusch et al 2005), the diversity of higher trophic levels, insects (Barton et al 2015; Crutsinger et al 2006; Johnson et al 2006), and ecosystem processes such as total biomass and water quality (Tomimatsu et al 2014). Invasive species provide an excellent opportunity to examine whether genotypic diversity enhances the spread of an invasive species
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