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

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.

Examining assumptions of soil microbial ecology in the monitoring of ecological restoration

“…The same may be true for SMC, though how important this is remains unclear (Austin, Vivanco, González‐Arzac, & Pérez, 2014; Rúa et al., 2016). Even if commercial products are able to establish in the field, they may not be resilient to natural conditions compared to local SMC (Griffiths & Philippot, 2013, Moreira‐Grez et al., 2019).…”

“…This aspect of microbial inoculant use is understudied, largely because there have been few longitudinal studies tracking inoculant fate in the field. More importantly, such changes and/or replacement of native microbial guilds can have a negative effect on native plant fitness (Moreira‐Grez et al., 2019). Consequences of shifts in SMC as a result of inoculants could have long‐lasting and unintended ecosystem‐level consequences.…”

Stockpiling disrupts the biological integrity of topsoil for ecological restoration

“…For example, Jasper et al (1989) found that inoculation with arbuscular mycorrhizal fungi increased plant growth and phosphorus uptake of Australian Acacia species in stockpiled topsoil. While there is growing interest in the use of commercially available inoculants in restoration, these products are likely not as effective as indigenous soil biota (Maltz and Treseder 2015;Moreira-Grez et al 2019;Valliere et al 2020), and this is an important avenue for future research.…”

Field-Deployed Extruded Seed Pellets Show Promise for Perennial Grass Establishment in Arid Zone Mine Rehabilitation

“…Commercially available microbes have been tested as potential fertilizer for improving plant performance in plant substrates, but often result in poor soil bacterial diversity, and may even be detrimental to plants in restoration (Moreira-Grez et al, 2019). By contrast with introduced exogenous microbes, translocated native soil microorganisms can positively interact with arid native plants promoting seedling growth of Pilbara species, e.g., Triodia spp.…”