Earthworms increase plant biomass more in soil with no earthworm legacy than in earthworm‐mediated soil, and favour late successional species in competition

Abstract

As ecosystem engineers, earthworms greatly affect plant communities. They create persistent soil structures enriched by nutrients that improve the conditions for plant growth and modify competition between plant species. We therefore hypothesized that earthworm activity would be more important in early stages of the primary succession, when the soil is not modified by earthworms, than in the late stages of the succession, when the soil is already improved by earthworms. On the other hand, earthworms also affect plants via many other effects such as seed predation or excreting hormone‐like compounds, which could make earthworm presence important in late successional soil. To explore earthworm effects on plant community succession, we performed a laboratory microcosm experiment without and with earthworms (Lumbricus rubellus and Aporrectodea caliginosa), with early successional plants (Poa compressa, Medicago lupulina and Daucus carota) and late successional plants (Arrhenatherum elatius, Lotus corniculatus and Plantago lanceolata) and with soil previously unaffected by earthworms (young soil) and soil substantially affected by earthworms (developed soil). These soils were taken from the early and late successional post‐mining sites of the Sokolov coal mining district (northwest Czech Republic). When both early and late successional plants were grown separately, earthworms increased plant biomass proportionally more in the young soil than in the developed soil, indicating that earthworm activity is more important in undeveloped than in developed soil. When early and late successional plants were competing each other, the biomass of the early successional plants was reduced. In the young soil, the reduction was independent of earthworm presence. In the developed soil, the reduction was promoted by the earthworms. Late successional plants profited from the reduction of early successional plants and increased their biomass. This increase was promoted by the earthworm presence. Our results indicate that the direct effects of earthworm presence on plants decrease during succession because of the cumulative effects of earthworm activity on soil conditions. Such ecosystem engineering effects favour late successional competitors and therefore promote the replacement of species during succession. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12999/suppinfo is available for this article.

Earthworms affect growth and competition between ectomycorrhizal and arbuscular mycorrhizal plants

“…pH and conductivity were determined in the same filtrate with a glass, potentiometric electrode. The data revealed that earthworm activity reduced the pH, increased the nitrate concentration, and tended to increase the soluble P concentration of the soil (Table ) which is in line with Mudrák and Frouz ().…”

“…Earthworms therefore have positive feedback effects on plant community composition and productivity (Thompson et al 1993, Scheu and Parkinson 1994, Brown et al 2000, Scheu 2003, Wurst et al 2005, Baker et al 2006, Roub ı ckov a et al 2009, Mudr ak et al 2012. Earlier field observation, and manipulation experiments, that was carried in the post-mining sites used in this study demonstrated a change of plant community following the earthworm colonization , Roub ı ckov a et al 2009, Mudr ak et al 2012, Mudr ak and Frouz 2018. Earthworm establishment in disturbed surfaces requires the amelioration of adverse conditions, for example, pH, stabilization of the physiochemical conditions in the soil, and availability of a suitable food supply (Curry 2004) which agrees with the reports of when earthworms colonize the post-mining area , Roub ı ckov a et al 2009, Mudr ak et al 2012.…”

“…Previous studies, done in the same sites, have shown that the herbaceous plants hosting AM fungi dominate during early successional stages but are replaced by the woody hosts of EcM fungi after 20-30 yr of spontaneous vegetation development; this transition may result from the competition between roots colonized by AM fungi and those colonized by EcM fungi . In later successional stages, however, earthworm invasion increases the density of late successional herbs that host AM fungi (Frouz et al 2008, Mudr ak andFrouz 2018). Based on these observations, we hypothesize that earthworm invasion not only improves conditions for plant growth but also reduces effectiveness of EcM against AM fungi concerning their hosts' level of competition for resources.…”

“…, Mudrák et al. , Mudrák and Frouz ). Earthworm establishment in disturbed surfaces requires the amelioration of adverse conditions, for example, pH, stabilization of the physiochemical conditions in the soil, and availability of a suitable food supply (Curry ) which agrees with the reports of when earthworms colonize the post‐mining area (Frouz et al.…”

“…In later successional stages, however, earthworm invasion increases the density of late successional herbs that host AM fungi (Frouz et al. , Mudrák and Frouz ). Based on these observations, we hypothesize that earthworm invasion not only improves conditions for plant growth but also reduces effectiveness of EcM against AM fungi concerning their hosts’ level of competition for resources.…”