Reconditioning Degraded Mine Site Soils With Exogenous Soil Microbes: Plant Fitness and Soil Microbiome Outcomes.

Benjamin Moreira-Grez,Khalil Kariman,Andrew S Whiteley,Paul Storer,Deepak Kumaresan,Miriam Muñoz-Rojas,Anthony G O’Donnell

doi:10.3389/fmicb.2019.01617

Abstract

Mining of mineral resources substantially alters both the above and below-ground soil ecosystem, which then requires rehabilitation back to a pre-mining state. For belowground rehabilitation, recovery of the soil microbiome to a state which can support key biogeochemical cycles, and effective plant colonization is usually required. One solution proposed has been to translate microbial inocula from agricultural systems to mine rehabilitation scenarios, as a means of reconditioning the soil microbiome for planting. Here, we experimentally determine both the aboveground plant fitness outcomes and belowground soil microbiome effects of a commercially available soil microbial inocula (SMI). We analyzed treatment effects at four levels of complexity; no SMI addition control, Nitrogen addition alone, SMI addition and SMI plus Nitrogen addition over a 12-week period. Our culture independent analyses indicated that SMIs had a differential response over the 12-week incubation period, where only a small number of the consortium members persisted in the semi-arid ecosystem, and generated variable plant fitness responses, likely due to plant-microbiome physiological mismatching and low survival rates of many of the SMI constituents. We suggest that new developments in custom-made SMIs to increase rehabilitation success in mine site restoration are required, primarily based upon the need for SMIs to be ecologically adapted to both the prevailing edaphic conditions and a wide range of plant species likely to be encountered.

Highlights

The mining of ores and minerals results in deleterious environmental outcomes (Bradshaw, 2000) such as clearance of landscape biota and the production of large amount of by-products
Soil pH, remained constant across the experimental treatments, except for topsoil initially amended with the soil microbial inocula (SMI) (Inoculum), where pH significantly decreased from Basal levels of 7.74 to 7.13 when the SMI was added (P ≤ 0.05) (Figure 1 and Supplementary Table 1)
We assessed soil microbiome and plant parameters as a first approach to gauge whether currently available SMIs can be applied to mine site restoration practices to enhance aboveground outcomes and overcome the reduced microbiome capacity within soils which have been subjected to mineral extraction (Kumaresan et al, 2017)

Summary

Introduction

The mining of ores and minerals results in deleterious environmental outcomes (Bradshaw, 2000) such as clearance of landscape biota and the production of large amount of by-products. There are significant declines in key traits such as carbon content, seed banks of locally adapted native plants, and the composition of the microbiome (Golos and Dixon, 2014; Muñoz-Rojas et al, 2016a), including community diversity, and function (Kumaresan et al, 2017) This decline in the soil microbiome is a critical factor within this stored topsoil, due to potential loss of key nutrient cycling pathways (Wagg et al, 2014) but growing evidence suggests that plant diversity, and fitness can be determined by the surrounding microbiome composition (Lau and Lennon, 2011, 2012; Panke-Buisse et al, 2015; Wubs et al, 2016). The addition of exogenous microbiomes in the form of soil microbial inocula (SMIs), such as those traditionally used in agricultural practices, is becoming increasingly mainstream in mine site restoration practices

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Discussion

Conclusion