Role of microtopography in the expression of soil propagule banks on reclamation sites

Microbial composition and function in reclaimed mine sites along a reclamation chronosequence become increasingly similar to undisturbed reference sites

Mine reclamation historically focuses on enhancing plant coverage to improve below and aboveground ecology. However, there is a great need to study the role of soil microorganisms in mine reclamation, particularly long-term studies that track the succession of microbial communities. Here, we investigate the trajectory of microbial communities of mining sites reclaimed between three and 26 years. We used high-throughput amplicon sequencing to characterize the bacterial and fungal communities. We quantified how similar the reclaimed sites were to unmined, undisturbed reference sites and explored the trajectory of microbial communities along the reclamation chronosequence. We also examined the ecological processes that shape the assembly of bacterial communities. Finally, we investigated the functional potential of the microbial communities through metagenomic sequencing. Our results reveal that the reclamation age significantly impacted the community compositions of bacterial and fungal communities. As the reclamation age increases, bacterial and fungal communities become similar to the unmined, undisturbed reference site, suggesting a favorable succession in microbial communities. The bacterial community assembly was also significantly impacted by reclamation age and was primarily driven by stochastic processes, indicating a lesser influence of environmental properties on the bacterial community. Furthermore, our read-based metagenomic analysis showed that the microbial communities' functional potential increasingly became similar to the reference sites. Additionally, we found that the plant richness increased with the reclamation age. Overall, our study shows that both above- and belowground ecological properties of reclaimed mine sites trend towards undisturbed sites with increasing reclamation age. Further, it demonstrates the importance of microbial genomics in tracking the trajectory of ecosystem reclamation.

Response of three native grass species on dry tailings reclamation substrate amended with petroleum coke

Surface mining around the world has produced large quantities of waste materials with ecological impacts. Oil sands mining in Canada generates large volumes of petroleum coke and tailings every year, which are stockpiled in the mining areas and must be reclaimed through capping or used in reclamation substrates. A greenhouse study was conducted to determine whether substrates of various mixes of dry tailings (DT), tailings sand (TS), and peat mineral mix (PMM) with coke amendment would support emergence and growth of three grass species commonly used in land reclamation. After 16 wk in the greenhouse, plant performance varied with substrate and amendment. Treatment with DT/TS/PMM (50:25:25) with 40% coke had greatest cover, biomass, and density and the best plant health. Plant growth was inhibited in treatments with DT (100%) and coke (100%) due to high concentrations of hydrocarbons, undesirable exchangeable ions, and salinity that restricted soil water retention (gravimetric water content, hydraulic conductivity) relative to treatments with PMM. Agrostis scabra Willd. and Festuca saximontana. showed poor growth or did not survive on DT and DT/TS with coke. Elymus trachycaulus (Link) Gould ex Shinners performed better in all DT mixes and performed the best in DT/TS/PMM with 40% coke. Results from this study indicate that mixing with PMM could improve the reclamation potential of DT and coke.

Legacies of past land use challenge grassland recovery – An example from dry grasslands on ancient burial mounds

Due to large-scale agricultural intensification, grasslands are often restricted to habitat islands in human-transformed landscapes. There are approximately half a million ancient burial mounds built by nomadic steppic tribes in the Eurasian steppe and forest steppe zones, which act as habitat islands for dry grassland vegetation. Land use intensification, such as arable farming and afforestation by non-native woody species are amongst the major threats for Eurasian dry grasslands, including grasslands on mounds. After the launch of the Good Agricultural and Environmental Condition framework of the European Union, in Hungary there is a tendency for ceasing crop production and cutting non-native woody plantations, in order to conserve these unique landmarks and restore the historical grassland vegetation on the mounds. In this study, restoration prospects of dry grassland habitats were studied on kurgans formerly covered by croplands and Robinia pseudoacacia plantations. Soil and vegetation characteristics were studied in thespontaneously recovering grasslands. The following questions were addressed: 1; How does site history affect the spontaneous grassland recovery? 2; Do residual soil nutrients play a role in grassland recovery? In former croplands, excess phosphorus, while in former Robinia plantations, excess nitrogen was present in the soil even four years after the land use change and grassland vegetation was in an early or mid-successional stage both on the mounds. The results showed that, without proper management measures, recovery of grassland vegetation is slow on mounds formerly used as cropland or black locust plantation. However, restoration efforts, focused on the restoration of mounds formerly covered by croplands, can be more effective compared to the restoration of mounds formerly covered by forest plantations.