Invasive earthworms change nutrient availability and uptake by forest understory plants

Abstract

Assess whether invasive earthworms alter nutrient dynamics in habitats they colonize. We investigated nutrient dynamics of forest soils and three native plant species (Acer saccharum, Polygonatum pubescens, Polystichum acrostichoides) along four earthworm invasion gradients in central New York. Earthworm biomass (a proxy for earthworm impact) was related to distribution and concentration of soil and plant nutrients. At shallower depths, earthworms were associated with lower total and exchangeable P, but higher Ca, K, Mg and Mn. Earthworm-invaded plots showed higher soil Ca and higher foliar Ca in A. saccharum and P. acrostichoides, and lower soil P with lower foliar P in P. pubescens. Presence of earthworms substantially decreased rooting volume in the A horizon, co-occurring with a build up of exchangeable nutrient concentrations and pools. Overall, earthworm biomass was a better predictor of foliar nutrient concentrations than either exchangeable or total nutrient concentrations and pools. Earthworms may create stressful rooting conditions, limiting rooting of native plants in the A horizon. The resulting plant-accessible nutrient pool that builds up in the A horizon of earthworm-invaded soils could provide a mechanism for the invasive success of non-indigenous plants that have an evolutionary association with earthworms in the native range and that follow earthworm invasions.