Abstract
Soils of abandoned and vacant lands in the periphery of cities are frequently subjected to illegal dumping and can undergo degradation processes such as depletion of organic matter and nutrients, reduced biodiversity, and the presence of contaminants, which may exert an intense abiotic stress on biological communities. Mycorrhizal-assisted phytoremediation and intercropping strategies are highly suitable options for remediation of these sites. A two-year field experiment was conducted at a peri-urban site contaminated with petroleum hydrocarbons and polychlorinated biphenyls, to assess the effects of plant growth (spontaneous plant species, Medicago sativa, and Populus × canadensis, alone vs. intercropped) and inoculation of a commercial arbuscular mycorrhizal and ectomycorrhizal inoculum. Contaminant degradation, plant performance, and biodiversity, as well as a variety of microbial indicators of soil health (microbial biomass, activity, and diversity parameters) were determined. The rhizosphere bacterial and fungal microbiomes were assessed by measuring the structural diversity and composition via amplicon sequencing. Establishment of spontaneous vegetation led to greater plant and soil microbial diversity. Intercropping enhanced the activity of soil enzymes involved in nutrient cycling. The mycorrhizal treatment was a key contributor to the establishment of intercropping with poplar and alfalfa. Inoculated and poplar-alfalfa intercropped soils had a higher microbial abundance than soils colonized by spontaneous vegetation. Our study provided evidence of the potential of mycorrhizal-assisted phytoremediation and intercropping strategies to improve soil health in degraded peri-urban areas.
Highlights
Abandonment of agricultural and industrial sites in the periphery of many cities often results in the presence of randomly distributed vacant areas that are highly vulnerable and susceptible to uncontrolled deposition of wastes, contributing to soil degradation and contamination (Németh and Langhorst, 2014; Gómez-Sagasti et al, 2018; Míguez et al, 2020)
The soil from the abandoned vacant land contained low concentrations of heavy metals (Cd, Cu, Zn, Pb) that did not exceed the Critical Reference Values for Ecosystem Protection established by Law 4/2015 of the Basque Country for agricultural settings (Government of the Basque Country, 2015)
In order to assess the effects of the treatments on contaminant degradation, we compared those plots with similar concentrations of contaminants just after treatment implementation (March 2017; t0) vs. at the end of the experiment (July 2018; tf)
Summary
Abandonment of agricultural and industrial sites in the periphery of many cities often results in the presence of randomly distributed vacant areas that are highly vulnerable and susceptible to uncontrolled deposition of wastes, contributing to soil degradation and contamination (Németh and Langhorst, 2014; Gómez-Sagasti et al, 2018; Míguez et al, 2020) Managed, these abandoned sites can be a valuable ecological resource, for instance by providing ecosystem services (Nassauer and Raskin, 2014; Herrmann et al, 2016) and harboring biodiversity (Delgado de la Flor et al, 2020; Perry et al, 2020), but can afford an opportunity for land redevelopment and economic and social benefits (Kim et al, 2018). Phytoremediation can gradually alleviate the potential environmental risks caused by contaminants and improve soil health (Vangronsveld et al, 2009)
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