Success in restoring native plant communities on kimberlite mining dumps in the Afro-alpine Drakensberg region of Lesotho.

Rehabilitation strategies for degraded mine dumps have generally seen limited success due to different complications associated with mining biophysical disturbance. In this study, we tested a combination of two methods to expedite revegetation of kimberlite tailings at Letseng Diamond Mine (i.e., in the Afro-alpine areas of Lesotho). We ran trials on different growth media located on fine and coarse kimberlite tailings (i.e. sites) mixed with different substrate combinations and topsoil and sowing a seed mix comprised of native plant species. Overall, as predicted, fine kimberlite tailings displayed significantly higher plant abundance than coarse kimberlite tailings, and sown seeds performed significantly better than spontaneous colonisation by emerging species. Kimberlite tailings mixed with topsoil (100 mm) showed significantly greater plant abundance, and similarly, when coarse kimberlite tailings were introduced to fine tailings. Physicochemical analyses of growth media components suggested that topsoil provided additional nutrients and that plants could readily access available nutrients in the fine kimberlite tailings. We noted a gradual significant increase in plant abundance over 5 years, enhanced by new plant species emerging from the topsoil seed bank or by natural seed dispersal. Although plant abundance differed significantly, both fine and coarse kimberlite tailings displayed high plant species diversity (H = 3.4 and D = 0.95 and H = 3.5 and D = 0.95, respectively). Out of 36 emerging plant species, 15 species spontaneously colonised both growth media. The significant variation in abundance among plant species between treatments was mostly attributed to dominant forb species, namely Chrysocoma ciliata, Glumicalyx montanus, Oxalis obliquifolia, Senecio inaequidens and Trifolium burchellianum. We have identified suitable growth media for plant community restoration on kimberlite tailings in the Drakensberg alpine area using a seed mix of native plant species in combination with natural seed dispersal from the surrounding pristine environment. We provide evidence for using two complementary approaches to optimise native plant community development during restoration in the Drakensberg alpine area.

The Influence of Serpentine Soil on the Early Development of a Non-Serpentine African Thistle, Berkheya radula (Harv.) De Wild.

Serpentine soils are rich in heavy metals and poor in nutrients, limiting plant species' performance and survival. Nevertheless, specificities of such limitations as well as adaptability features required for thriving in serpentine environments are barely known. The Barberton Greenstone Belt in South Africa is an example of an area containing serpentine soil with adapted vegetation. In this study, a pot experiment was performed to compare development features (i.e., germination rates, leaf count, leaf length, biomass and photosynthetic capacity) during the early development of the non-serpentine species Berkheya radula, a genus consisting of known metal hyperaccumulators from serpentine areas in South Africa. B. radula was grown in serpentine soils taken from the Barberton region. B. radula leaves had heavy metals in concentrations that confirmed the species as a phytoextractor. There were trends for enhanced productivity and photosynthesis in the serpentine treatments compared to the control. Leaf count, leaf length, electron transport efficiency (ψEo/(1 - ψEo), density of reaction centers and PIABS,total were significantly and positively correlated with at least one of the heavy metals in the leaves. Germination rates were positively influenced by K, whereas biomass and the density of reaction centers were negatively affected by Ca and P, and only Ca, respectively. The heavy metals Zn, Ni and Co were positively correlated with each other, whereas they were negatively correlated with the macronutrients K, Ca and P. The latter correlated positively with each other, confirming higher fertility of the control soil. Our study suggests that B. radula exhibits metallophyte characteristics (i.e., preadapted), despite not naturally occurring on metal-enriched soil, and this provides evidence that the potential for bioaccumulation and phytoremediation is shared between serpentine and non-serpentine species in this genus.

Influence of land use and topography on distribution and bioaccumulation of potentially toxic metals in soil and plant leaves: A case study from Sekhukhuneland, South Africa.

Potentially toxic metal (PTM) enrichment of the soil-plant system in ultramafic and mining regions is a global concern as it affects the food chain. With expanding mining industry, it is important to assess if anthropogenic factors (i.e., land use practices) have a greater influence in this regard compared to natural factors (i.e., topography). Localities in Sekhukhuneland, South Africa, were selected along an altitudinal gradient (i.e., topography: upper slope, footslope, valley and valley bottom) and a land use profile (i.e., rangelands, gardens, tailings and wastelands) to investigate the distribution of Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Sr and Zn of natural (i.e., ultramafic geology) and anthropogenic (i.e., mining) origin in surface soil and plant leaf tissue. Plant life form was considered as an additional factor to evaluate PTM accumulation in leaves. Findings revealed a wider distribution range for Cr and Ni in the surface soil. Co, Cu, Mg, Mo, Sr and Zn were accumulated (bioaccumulation factor, BAF > 1) in leaf tissue of 74% of the evaluated plants of which 83% were indigenous. Grasses, forbs, dwarf shrubs and shrubs showed the highest accumulation levels. Despite an observed trend in the distribution of PTMs in soils and plant leaves along the altitudinal gradient, no significant differences were determined among the topographic positions. Land use practices, however, differed significantly indicating anthropogenic interference as a predominant determinant of PTM enrichment of soil-plant systems. Metal tolerant dominant plants in Sekhukhuneland could be classified as metallophytes. Indigenous species, accumulators and excluders, showed prospects for phytoremediation and rehabilitation of metal contaminated sites, respectively. Concentrations of Cr and Co in food and medicinal plant leaves exceeded the international permissible limits, which highlighted the necessity to estimate human health risks for PTMs in metalliferous sites.