The global invader Ligustrum lucidum accumulates beneficial arbuscular mycorrhizal fungi in a novel range

Abstract

Alien invasive trees may expand and form monospecific forests by enhancing mutualism with arbuscular mycorrhizal fungi (AMF) and/or preventing the establishment of other plants through accumulation of antagonists for native plants. The success of invasive plants also has been associated with their higher phenotypic plasticity. Here we tested these mechanisms by studying the global invasive tree Ligustrum lucidum (hereafter Ligustrum) and the dominant native tree of the Chaquean montane forest (central Argentina) Lithraea molleoides (hereafter Lithraea). We experimentally addressed the effects of soil biota from Ligustrum monospecific forest stands and native montane forests on growth, biomass allocation, and nutrition of alien Ligustrum and native Lithraea. Soil biota was recovered from the rooting zone of adult trees of both species in each forest type. We found that arbuscule colonization in Ligustrum roots was significantly higher in seedlings grown with AMF communities from monospecific invaded forests in comparison to native soils. Mycorrhizal colonization in Lithraea roots did not differed between forest types. Soil biota from the rooting zone of the native Lithraea had no major effects on both itself and the invasive Ligustrum. Instead, AMF from Ligustrum rooting zone almost tripled and doubled P nutrition of the alien and the native compared with non-AMF treatments, respectively. Besides, antagonistic effects of soil biota were not observed. Lithraea root mass fraction (root mass/total plant mass, RMF) was not affected by forest type nor by soil treatment but Ligustrum RMF was affected by both factors. In particular, RMF decreased when seedlings grew with AMF from its rooting zone. The observed positive plant–soil feedback and the phenotypic plasticity of Ligustrum could explain, at least in part, the high invasiveness and the formation of monospecific forest stands by this global invader.