The relationships between functional and physicochemical soil parameters in metal(loid) mine tailings from Mediterranean semiarid areas support the value of spontaneous vegetation colonization for phytomanagement

Abstract

Spontaneous growth of native vegetation in abandoned metal(loid) mine tailings can be valuable for phytomanagement restoration projects. This study aimed to assess the degree to which spontaneous plant colonization of abandoned metal(loid) mine tailings from Mediterranean semiarid areas led to functional soil improvement, and to identify, if possible, a critical level indicating that this functionality was moving towards that of the vegetated soils from the surroundings. Vegetation ecological indexes, plant life forms and species functional roles, together with physicochemical and functional soils parameters, were studied in metal(loid) mine tailings abandoned ~40 years ago and surrounding forests in SE Spain. Vegetation patches showed only small differences in physicochemical parameters related to soil abiotic stress conditions (pH, salinity and metals), regardless of the vegetation. However, vegetation patches with greater species diversity and richness and presence of plants with contrasted life forms and functional traits that facilitate the growth of less stress-tolerant species showed an increase of the soil microbial functionality (higher microbial biomass C, β-glucosidase activity, bacterial metabolic activity and functional diversity). Moreover, these vegetation patches showed a functional soil status comparable to that of the forests outside the mine tailings. In this sense, the present study showed the value of preserving these vegetation patches since they may act as nucleation spots favoring positive plant-soil feedbacks that may help to accelerate the functional recovery of these degraded areas. Furthermore, strategies to promote the creation of new vegetation patches including a variety of species with contrasted life forms and functional traits should be considered in phytomanagement restoration projects for abandoned metal(loid) mine tailings.The present study was supported by the project RESCLICONT (CGL2016-80981-R), funded by the Ministry of Science, Innovation and Universities of Spain through FEDER funds; by the project METOXCLIM (PTDC/CTA-AMB/29557/2017), funded by FEDER, through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI), and by national funds (OE), through FCT/MCTES. Thanks are due to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020), through national funds. A. Peñalver-Alcalá was hired by the project RESCLICONT and received a grant from the Technical University of Cartagena for a short stay at the University of Aveiro. S. Peixoto holds a PhD grant (SFRH/BD/117738/2016) from FCT. I. Silva received a research fellowship from the METOXCLIM project (BI/CESAM/0063/METOXCLIM/2018). A.R.R. Silva received a research fellowship from the METOXCLIM project (BI/CESAM/00060/METOXCLIM/2018). M.N. González-Alcaraz holds a Saavedra Fajardo research contract from the Séneca Foundation of the Murcia Region. The authors thank F.J. Jiménez-Cárceles from Biocyma S.L. for his valuable help with vegetation fieldwork