Up to 800,000 km2 of land is impacted by mining activity globally. Whilst quarrying and open-cast mining is and will remain of great economic importance, quarrying leads to soil disturbance, destruction of habitats and large pit lakes can lead to evaporative loss of groundwater. Different technical reclamation approaches include covering the quarry with fertile topsoil then sowing with seed mixtures.
A study led by Tanel Vahter, PhD student at the Plant Ecology Lab at the University of Tartu (Estonia) and his supervisor by Dr Maarja Öpik, investigated whether co-introducing native arbuscular mycorrhizal (AM) fungi with native plants leads boosts biodiversity restoration. Vahter and colleagues from Sweden and Saudi Arabia found that the availability of symbiotic AM fungi led to higher plant richness, diversity and abundance. Dr Maarja Öpik was the leading scientist for establishing the MaarjAM online database of arbuscular mycorrhizal fungi.
Vahter and colleagues set up experimental plots at three, post-mining oil shale quarries in Estonia for two years. First, they collected some “target soil” containing local soil biota from a 50-year-old restored mining site and added gardening soil. To ‘trap culture’ AM fungi, a mixture of three native grass and 11 native forb species were grown for 18 weeks on the soil mixture. After one month of winter conditions to allow vernalisation of the fungi, the scientists removed the above-ground plant biomass and set up field experiments with this soil inoculum.
The researchers applied either soil inoculum only, plant seeds only, both soil inoculum and plant seeds or nothing on the individual 2 m x 2 m plots and mulched the top with a thin layer of straws. The plant richness was counted and AM fungal richness was calculated from soil DNA sequencing. Soil fatty acid biomarker analysis quantified the total fungal, bacterial and AM fungal biomass in soil samples.
Plots which received both the soil inoculum and seed mixture has the highest plant and AM fungal richness across the three sites. In the first and second year, 34 and 49 plant species grew respectively and half of the soil AM fungi belonged to the genera Glomus and Claroideoglomus. Whilst the AM fungal community composition did not differ greatly between treatments, the plant community composition did.
“We observed a clear effect of AM fungal and plant propagule introductions, with cointroduction of plants and symbiotic fungi increasing the diversity and abundance of both groups more than the introduction of either group alone”, Vahter and colleagues explained. “[T]he availability of plant seeds (dispersal limitation) rather than seedling establishment (establishment limitation) initially limits vegetation recovery at these post-mining sites.”
“The order of arrival of the symbiotic partners in new habitat patches may be important, with the ‘plants arriving first’ scenario potentially more beneficial for vegetation recovery than ‘AM fungi arriving first’ because of the limited number of fungal germinations possible for a single spore without successful root contact”, Vahter and colleagues explained.
This study shows how important soil organisms are for quarry restoration and how it could be applied in the future. In China alone, the average consumption of limestone used to produce cement exceeded 2.5 billion tons per year between 2010-2016, novel ideas of land restoration for post-mining areas are much needed.