Secondary organic aerosol (SOA) formed from wildfire/biomass-burning emissions (BB) represents a significant fraction of global SOA production. However, there are large uncertainties in representing BB-SOA in climate models. We studied the evolution of organic aerosols (OA) from burning three biomass samples─savannah grass, savannah wood, and boreal forest surface─under different combustion conditions and during daytime (photochemical oxidation) and nighttime (dark oxidation) aging in an atmospheric chamber. OA dominated the BB emissions by contributing ∼82-99% of the total PM1 mass. Atmospheric aging by both oxidation processes produced comparable amounts of net OA mass. We show, with PMF analysis, that this is connected to the more efficient loss of primary OA, which compensates for the more efficient gas-phase oxidation during daytime aging compared with nighttime. The observed moderate OA mass enhancement (0.75-1.3 times) agrees well with field observations, thereby addressing the discrepancy between laboratory and field studies. For both aging scenarios, total OA emission factors after aging are similar to those of primary OA, providing new insights into the evolution of BB emissions. Our results suggest a simplified treatment of OA in climate models in remote areas with low NOx concentrations.

ABSTRACT Biological soil crusts (biocrusts) shape surface ecosystem processes, but how serpentinite geochemistry and moisture structure their microbial communities remains unclear. We collected biocrust samples from serpentine and nonserpentine areas under frequent and erratic moisture regimes from the Barberton Greenstone Belt, South Africa. Bacterial communities were analyzed using 16S rRNA gene sequencing and shotgun metagenomics. Coarse bacterial diversity measures (alpha diversity and phylum‐level composition) did not differ significantly between soil types or moisture regimes. However, amplicon sequence variant (ASV)‐level analyses combining differential abundance testing, indicator‐species analysis, and Spearman's correlations ( ρ ≥ 0.75, p ≤ 0.05) identified taxa linked to soil chemistry and moisture. Three hundred sixty ASVs differed between soil types (199 enriched in serpentine) and 240 differed by moisture regime within serpentine soils (220 enriched under erratic moisture). Many serpentine‐associated microbes (e.g., Solirubrobacterales, Blastocatella , Mycobacterium , Chloroflexi clades) were linked to elevated nickel, cobalt, chromium, manganese, and iron, and sometimes to low‐calcium environments, reflecting tolerance to metal toxicity and characteristic serpentine geochemistry. In contrast, metabolic pathways were comparatively constrained across soils and moisture. Few pathways differed significantly, and no combined effect of soil type and moisture was detected on overall functional composition. In serpentine biocrusts, the moisture regime shaped the distribution of microbial functions without altering overall pathway composition. Erratic moisture was associated with enrichment of pathways linked to stress tolerance and detoxification. Frequent moisture was associated with greater representation of fermentation‐related pathways and cell‐envelope biosynthesis. Benchmarking showed that PICRUSt2 recovered broad sample‐level patterns but poorly captured pathway‐specific quantitative variation relative to HUMAnN3.

Urban areas are foci for the introduction of non‐native plant species, and they often act as launching sites for invasions into the wider environment. Although interest in biological invasions in urban areas is growing rapidly, and the extent and complexity of problems associated with invasions in these systems have increased, data on the composition and numbers of non‐native plants in urbanized areas remain scattered and idiosyncratic. We assembled data from multiple sources to create the Global Urban Biological Invasions Compendium (GUBIC) for vascular plants representing 553 urban centres from 61 countries across every continent except Antarctica. The GUBIC repository includes 8140 non‐native plant species from 253 families. The number of urban centres in which these non‐native species occurred had a log‐normal distribution, with 65.2% of non‐native species occurring in fewer than 10 urban centres. Practical implications : The dataset has wider applications for urban ecology, invasion biology, macroecology, conservation, urban planning and sustainability. We hope this dataset will stimulate future research in invasion ecology related to the diversity and distributional patterns of non‐native flora across urban centres worldwide. Further, this information should aid the early detection and risk assessment of potential invasive species, inform policy development and assist in setting management priorities.

Warming climate is predicted to increase forest fires which can be a major source of black and brown carbon (BC and BrC) into the atmosphere. Unlike North American forest fires, very limited studies have characterized North Eurasian biomass burning (BB) emissions. In this work, we determined the emission factors (EF) of carbonaceous aerosols and characterized light absorption of BrC emitted from boreal and peat burning through offline filter extraction method. The results were compared to African savanna emissions. Effects of atmospheric dilution and oxidative aging on BrC absorptivity were investigated for selected BB emissions sampled into an environmental chamber. Organic carbon (OC) and elemental carbon (EC) EFs of fresh BB emissions ranged between 1.30–89.9 and 0.01–4.80 g kg−1 respectively. Methanol soluble OC (MSOC) represented more than 92 % of fresh BB emissions, irrespective of fuel type, and consisted of weakly absorbing BrC with imaginary refractive index at 550 nm (kMSOC_550) ranging from 0.002 to 0.011. Water soluble OC (WSOC) fractions varied among fresh BB emissions but overall exhibited higher mass absorption efficiencies at 365 nm (MAE365) than MSOC. Dilution-related evaporative loss in environmental chamber resulted in less volatile OC, making them less soluble in methanol. Photochemical and dark oxidative aging further increased the low volatility OC fractions of the organics along with its oxidation state. Our estimated OC-EC emission factors and kMSOC for fresh BB emissions can be used for future modelling purposes. Further online measurements are needed to account for non-soluble strong BrC in aged BB emissions.

Fire is an integral part of savanna and grassland biomes and globally approximately half of landscape fire emissions originate from savannas and grasslands. Emissions of trace gases and aerosol particles from landscape fires are characterised by emission factors (EFs), which denote the amount of emitted substance per mass of combusted biomass. EFs vary depending on both the biomass that is consumed in the fire and the combustion characteristics of the fire, i.e. the ratio of flaming to smouldering combustion. However, emission inventories tend to use only one average EF for each biome. Here, we use a set of 27 laboratory experiments to characterise the effect of combustion characteristics on submicron aerosol EFs from savanna and grassland biomass acquired from South Africa as well as boreal forest floor samples from Finland. Combustion experiments were carried out at the ILMARI facility in Kuopio, Finland from May to June 2022 under an open stack mimicking natural burning and dilution. Sample was injected into a 29 m3 environmental chamber for ageing studies. Chemical and physical properties of both fresh and aged smoke were observed with a host of instruments including e.g. AMS, FIGAERO-CIMS, VOCUS, SP2 and SMPS. The ratio of flaming to smouldering combustion was characterised by modified combustion efficiency (MCE), i.e. CO2/(CO2+CO). The increase of organic aerosol EF with increasing smouldering fraction (i.e. decreasing MCE) was very similar for both the grassland and savanna combustion experiments. Surprisingly, also the boreal forest floor EFs closely follow the same trend, where smouldering-dominated combustion EFs are more than 10 times higher than EFs for flaming combustion. We observed also that the submicron aerosol particle size distribution shifts towards larger sized particles with increasing smouldering fraction. Furthermore, both the number and the mass of the size distribution cannot be fully characterised with a single log-normal size distribution, which needs to be considered when converting mass emissions into number size distribution in simulations.

The growth potential of Crinum bulbispermum was evaluated on gold mine tailings. The primary objectives were to model the species’ climatic niche in relation to gold mining regions, assess its germination success on tailings, and compare seedling survival and growth on tailings versus other soil types. Species distribution modelling identified the South African Grassland Biome on the Highveld (1000+ m above sea level), where the majority of gold mines are located, as highly suitable for the species. Pot trials demonstrated above 85% germination success across all soil treatments, including gold mine tailings, indicating its potential for restoration through direct seeding. An initial seedling establishment rate of 100% further demonstrated the species’ resilience to mine tailings, which are often seasonally dry, nutrient-poor, and may contain potentially toxic metals. However, while C. bulbispermum was able to germinate and establish in mine tailings, long-term growth potential (over 12 months) was constrained by low organic carbon content (0.11%) and high salinity (194.50 mS/m). These findings underscore the critical role of soil chemistry and organic matter in supporting long-term plant establishment and growth on gold tailings. Building on previous research, this study confirms the ability of this thick-rooted geophyte to tolerate chemically extreme soil conditions. Crinum bulbispermum shows promise for phytostabilization and as a potential medicinal plant crop on tailings. However, future research on microbial community interactions and soil amendment strategies is essential to ensure its long-term sustainability.

Weed responses in disturbance-prone agroecosystems are linked to specific plant traits that enable their persistence. Understanding how weeds adapt to thrive in these systems in response to herbicide application is important for farmers to improve weed management for enhanced crop productivity. In this study, we investigated the functional traits and types of weed species able to persist within fields of glyphosate-tolerant maize in the Oliver Tambo District of the Eastern Cape Province, South Africa. This was accomplished by exploring the abundance patterns, composition, and richness of specific weed traits and functional types. Frequency measures (%) were used to identify indicator species. A data set comprising 42 indicator weed species and 11 predefined disturbance traits from 28 fields of glyphosate-tolerant maize was considered for functional analysis. Clusters were identified according to the grouping of weed species based on their trait scores, which revealed ten plant functional types (PFTs). Disturbances associated with post-emergence (after ploughing, sowing, and herbicide application) act as filters that select for weed species with traits such as life span, life form, growth form, photosynthetic pathway, carbon storage, and nitrogen-fixing ability to colonise fields. Trait richness did not differ significantly across maize fields. Our results highlighted the functional types and traits that are favourable to weed resistance and survival, and these need to be considered when developing different herbicide application protocols. By understanding which traits are favourable for weed survival post-emergence, farmers can apply targeted weed management to safeguard maize productivity. In addition, successful control of weeds will contribute to landscape-targeted herbicide applications that are less harmful to the environment.

Serpentine soils are characterized by nutrient imbalances and high levels of potentially toxic metals (PTMs). These soils host depauperate plant communities of species with specialized adaptations. Initial studies showed that South African serpentine soils harbor distinct biocrust algal and cyanobacterial species compared to adjacent non-serpentine soils, with these communities further differing based on high and low precipitation levels. Here, we investigated the bacterial and fungal diversity of biological soil crusts from serpentine and non-serpentine soils at two precipitation levels. The bacterial and fungal communities were characterized using 16S rDNA and ITS metabarcoding, respectively. No significant differences could be found in bacterial richness and community structure. Nevertheless, bacterial taxa such as Archangium, Candidatus Solibacter, Chthoniobacter, and Microvirga were more abundant in serpentine biocrusts or biocrusts receiving lower precipitation. The fungal community structure was distinct between serpentine and non-serpentine soils (p = 0.027) and between high and low precipitation (p = 0.018). Furthermore, fungal diversity was lowest in the drier, serpentine biocrusts compared to non-serpentine (p = 0.001) and serpentine crusts receiving higher precipitation (p = 0.002). The fungal genera, Ramimonilia and Vishniacozyma, which are known to be resistant or tolerant to PTMs and other environmental extremes, were significantly more abundant (p = 0.036 and p = 0.016, respectively) in serpentine biocrusts, with the latter indicating serpentine habitats. This study concluded that soil type influenced the fungal alpha diversity, specifically in the serpentine soil, resulting in a decrease in fungal species richness. Furthermore, precipitation influenced fungal beta diversity by shaping distinct fungal communities found in the biocrusts of serpentine and non-serpentine soils. We investigated bacterial and fungal diversity in biocrusts from serpentine and non-serpentine soil in South Africa. While bacterial diversity showed no significant differences, fungal community structure varied significantly between serpentine (S) and non-serpentine (NS) biocrusts and between precipitation levels. Soil type influenced fungal alpha diversity, particularly in serpentine soil, leading to decreased fungal species richness. In both serpentine and non-serpentine biocrusts, precipitation shaped fungal beta diversity, resulting in distinct fungal communities. image

AbstractRehabilitation 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.

Ancient grasslands are lost through transformation to agriculture, mining, and urban expansion. Land-use change leads to ecosystem degradation and a subsequent loss of biodiversity. Globally, degraded grasslands have become a priority for restoration efforts to recover lost ecosystem services. Although the ecological and social benefits of woody species and grasses are well documented, limited research has considered the use of forbs for restoration purposes despite their benefits (e.g., C sequestration and medicinal uses). The aim of this study was to determine if Crinum bulbispermum (Burm.f.) Milne-Redh. & Schweick., a medicinal geophyte, could form part of restoration initiatives to restore mine soils in grasslands of the South African Highveld. A pot experiment was conducted to assess the performance of C. bulbispermum in a random design, with three soil treatments varying in level of degradation and metal contamination. The plants were monitored for 12 months, and the morphological characters were measured monthly to assess performance and survival. Inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the soil and plant tissue concentration of potentially toxic metals. The results indicated that mine tailings negatively affected the growth and development of C. bulbispermum. Although the survival rates indicated that it could survive on tailings, its below-par productivity indicated that the species is not ideal for restoration purposes unless the tailings are ameliorated with topsoil. Although there was root accumulation of metals (Co, Cd, Cu, Mo, and Zn), there was no translocation to the bulbs and leaves, which makes C. bulbispermum suitable for medicinal use even when grown on metal-enriched soil. This species may not be viable for phytoremediation but is a contender to be used in phytostabilization due to its ecological advantages and the fact that it does not accumulate or store metals. These findings underscore the importance of considering geophytes in grassland restoration strategies, expanding their ecological and societal benefits beyond conventional approaches.

Potentially toxic metals and metalloids (PTMs) may become a concern to plant and animal health when soil concentrations exceed toxicity limits. These limits are often exceeded in polluted environments (anthropogenic sources) and may transfer through the trophic system, from contaminated soil to plants, and thereafter to herbivores and predators. The aim of this mini review was to consider trophic transfer of PTMs in terrestrial ecosystems, focusing on arthropods as the endpoint. ScienceDirect® was used as search engine with a set of keywords. The most assessed PTMs were Cd, Pb, and Zn, and 63% of all PTMs considered in research were attributed to anthropogenic sources. Industrial or mining sites were most frequently studied, and agricultural sites the least. Brassica was the most studied plant genus as the main extractor of PTMs from the soil as they are easy growing food plants known to take up PTMs. Research mostly focused on primary consumers, with Coleoptera being the most investigated arthropod order, probably because of the diversity of the order and its common occurrence worldwide. Most research was conducted in Europe, while South America and Africa only contributed 6.8% and 2.6%, respectively. The majority of the investigated articles (61%) assessed trophic transfer. From those, only 24% directly measured PTM transfer with experimental trials and included only one trophic level, that is, primary consumers, while 7% of research directly measured PTM transfer across multiple trophic levels (primary and secondary consumers).

Sub-Saharan Africa is under-represented in global biodiversity datasets, particularly regarding the impact of land use on species’ population abundances. Drawing on recent advances in expert elicitation to ensure data consistency, 200 experts were convened using a modified-Delphi process to estimate ‘intactness scores’: the remaining proportion of an ‘intact’ reference population of a species group in a particular land use, on a scale from 0 (no remaining individuals) to 1 (same abundance as the reference) and, in rare cases, to 2 (populations that thrive in human-modified landscapes). The resulting bii4africa dataset contains intactness scores representing terrestrial vertebrates (tetrapods: ±5,400 amphibians, reptiles, birds, mammals) and vascular plants (±45,000 forbs, graminoids, trees, shrubs) in sub-Saharan Africa across the region’s major land uses (urban, cropland, rangeland, plantation, protected, etc.) and intensities (e.g., large-scale vs smallholder cropland). This dataset was co-produced as part of the Biodiversity Intactness Index for Africa Project. Additional uses include assessing ecosystem condition; rectifying geographic/taxonomic biases in global biodiversity indicators and maps; and informing the Red List of Ecosystems.

Many threatened plant species in South Africa occur outside of protected areas and these include numerous succulent species that are traded internationally. Despite the potential impact that this may have on rare and endemic succulent species, limited population data exist to inform the non-detriment findings required by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) to ensure that international trade is sustainable. A concerted effort is being made in South Africa to gather such data for threatened succulents in the Euphorbiaceae. As part of this effort, the study set out to locate the extant populations of Euphorbia schoenlandii, an endemic of the Succulent Karoo, and acquire a better understanding of the population biology and ecology of the species. We applied the point-centred quarter method to estimate population size and density at each locality. This first-ever comprehensive field survey allowed for the determination of the geographic distribution of the species, as well as the sizes and number of populations. Biotic and abiotic environmental variables were employed to generate a habitat profile and a species distribution model for conservation purposes. Population structure, regeneration potential, and stability of the three known populations were also assessed. According to this study, approximately 29 152 individuals remain in the wild. It was shown that the species is often associated with nurse plants. Various potential pollinators were identified, but of concern was the considerable infestation by an alien snout moth (Nephopteryx divisella), a known pest of euphorbias. The first adult size class contained the highest proportion of individuals, which is indicative of pulse recruitment. Seedling numbers were low, most likely because the surveys were conducted during a drought period. Overall, this study provides the first data on various aspects of the population structure and ecology of E. schoenlandii. It provides valuable information regarding current threats, and also highlights the vulnerability of the species to further habitat loss and degradation or future illegal or unregulated harvesting.

We are describing here Stylochaeton glaucophyllum and S. sekhukhuniense, two new species from northeastern South Africa. Both species have a restricted distribution and are endemic to the Sekhukhuneland Centre of Plant Endemism, Limpopo and Mpumalanga Provinces, South Africa. The new species occur sympatrically with S. natalense, but never with one another. Stylochaeton glaucophyllum prefers norite and pyroxenite hills and mountains, whereas S. sekhukhuniense is associated with similar rock types in low-lying rocky areas. Both new species have the base of the spadix and infructescence partly below-ground and are mainly associated with open savannah. Stylochaeton glaucophyllum can be distinguished from S. sekhukhuniense in having greenish blue leaves with linear lobes while S. sekhukhuniense has green leaves with elliptic lobes. The leaves of S. glaucophyllum are longer (112–332 mm) than those of S. sekhukhuniense (44–180 mm). The petiolar sheath of S. sekhukhuniense extends into two slender, curling ligulae which are absent in S. glaucophyllum. Also included here is a key to the seven currently accepted species of Stylochaeton in southern Africa (South Africa, Eswatini, Zimbabwe and Mozambique).

Abstract. Kwinda M, Siebert SJ, Coller HV, Masehela TS. 2023. Composition and diversity patterns of weeds in herbicide tolerant maize fields and margins in the Eastern Cape, South Africa. Biodiversitas 24: 399-414. Weeds are considered undesirable plants that grow where they are not wanted, as they often outcompete crops and other beneficial species. This study aimed to compare species composition and diversity of weedy plant communities in fields planted with herbicide tolerant maize and associated field margins in the Eastern Cape Province, South Africa. A total of 88 weed species, representing 31 families were recorded from 244 plots for maize fields and field margins combined. The maize fields and margins across the four sites shared 53% of species. Non-metric Multidimensional Scaling grouped maize fields and field margins separately based on weed species composition. Moreover, maize fields and margins differed significantly in terms of Simpson (p=0.044) and Shannon indices (p=0.003), with diversity being higher in the fields. This study confirms that maize fields have a dissimilar composition of weedy species and dissimilar diversity, which differs from those of field margins. This result enables farmers to know whether current herbicide use is sufficient for targeted weed control. The findings and knowledge will benefit maize farmers and future researchers working on weeds in Sub-Saharan Africa when it comes to the development, implementation, and prioritization of various herbicide-based weed management protocols to ensure maximum crop productivity.

Metal hyperaccumulators accumulate particular metals or metalloids in their leaves to concentrations hun-dreds or thousands of times greater than is normal for most plants. Globally, Ni is the most often hyperaccu-mulated metal, with 532 hyperaccumulator species documented to date. Hyperaccumulators have attracted much attention as potential candidates for green technologies, including phytoremediation and agromining. In South Africa, six serpentinite-associated plants in the genera Berkheya and Senecio hyperaccumulate Ni (to > 0.1% of leaf tissue dry weight). It is surprising that only six of about 70 Berkheya and 290 Senecio species native to South Africa hyperaccumulate Ni, given about-10-20% of taxa from each genus occur on serpen-tinite. While it is costly and time consuming to field collect and chemically analyze leaves of all species in these genera, a novel method (portable X-Ray Fluorescence or pXRF analysis of herbarium specimens) allows for rapid (100 s of specimens/day) and non-destructive measurement of Ni in dry herbarium specimens. We tested the accuracy of this approach on known Ni hyperaccumulators vouchered at two South African herba-ria (C.E. Moss Herbarium (J) of the University of the Witwatersrand and A.P. Goossens Herbarium (PUC) from North-West University). While the absolute concentrations of Ni determined by ICP-MS and pXRF were not always directly in agreement, we had 100% success in confirming those that were known to hyperaccumulate Ni with those that did not. We propose pXRF as a cheap, effective, and efficient approach to rapidly screen herbarium specimens across South Africa to discover additional metal hyperaccumulators for much-needed remediation purposes.(c) 2023 Published by Elsevier B.V. on behalf of SAAB.

Gypsum is a soft sulfate mineral (CaSO 4 •2H 2 O) that forms deposits along the coast from southern Angola to South Africa and into the interior of South Africa (Figure 1).In some areas of the Namib Desert, pure gypsic deposits of up to 4 m deep and extending up to 100 km inland have been reported. 1Detailed geological maps for gypsiferous deposits in southern Africa are not readily available 2 , thus characterisation of gypsum distribution, depth of the soil profile, and gypsum content (%), is a crucial first step to study the region's gypsum ecosystems.

Ultramafic ecosystems are renowned for high endemism and habitat specialization. However, most of our understanding of ultramafic plant ecology comes from Mediterranean and temperate climes, raising questions about the generalizability of plant responses to ultramafic soils. This is especially apparent in tropical ultramafic ecosystems which exhibit a wide range of endemism and differentiation between ultramafic and adjacent non-ultramafic soils. Our objectives were two-fold: 1) synthesize our understanding of tropical ultramafic plant ecology, paying particular attention to generalities that may explain variation in endemism and habitat specialization among tropical ultramafic ecosystems; and 2) define an interdisciplinary research agenda using tropical ultramafic ecosystems as a macroecological model. We demonstrate that tropical ultramafic floras are diverse and variable in plant form and function due to the interactive effects of biogeography, climate, and edaphic properties. The variable rates of endemism, specialization, and stress tolerance traits across tropical ultramafic ecosystems have implications for the management and conservation of these diverse systems. Resumen. Los ecosistemas ultramáficos son reconocidos por su endemismo y especialización del hábitat. Sin embargo, la mayor parte de nuestra comprensión de la ecología vegetal ultramáfica proviene de climas mediterráneos y templados, lo que plantea dudas sobre la generalización de las respuestas de las plantas a los suelos ultramáficos. Esto es especialmente evidente en los ecosistemas tropicales ultramáficos que exhiben una amplia gama de endemismo y diferenciación entre suelos tropicales ultramáficos y no ultramáficos adyacentes. Nosotros teníamos dos objetivos: 1) sintetizar nuestra comprensión actual de la ecología de las plantas tropicales ultramáficas, prestando especial atención a las generalidades que pueden explicar la variación en el endemismo y la especialización del hábitat entre los ecosistemas tropicales ultramáficos; y 2) definir una agenda de investigación interdisciplinaria utilizando ecosistemas ultramáficos tropicales como modelo macroecológico. Las floras tropicales ultramáficas son diversas y variables en la forma y función de las plantas debido a los efectos interactivos de la biogeografía, el clima y las propiedades edáficas. Las tasas variables de endemismo, especialización y rasgos de tolerancia al estrés en los ecosistemas tropicales ultramáficos tienen implicaciones para el manejo y conservación de estos diversos sistemas.

Mine tailings are a source of potentially toxic metals (PTMs) worldwide. Phytoremediation is a low-cost green technology that uses metal-tolerant plants to extract these contaminants and rehabilitate the soil. In mine tailing restoration efforts, it can be beneficial to introduce species that can facilitate the colonization of other plants (i.e., nurse plant syndrome). In this study, the phytoremediation and nursing potential of two species adapted to metalliferous soil, Aloe burgersfortensis and A. castanea, were evaluated for the first time. An experiment was performed with aloe plants grown in pots containing potting soil, platinum tailings, and gold tailings. Leaves were assessed for bioaccumulation of PTMs. Seeds of Bermuda grass and African daisy, two successional pioneers, were planted with the aloes and had their developmental parameters evaluated after 30 days. Allelopathic effects were also assessed, with seeds of the pioneer plants infused with root extracts of the aloes from the different soil treatments. A. castanea demonstrated greater potential for the bioaccumulation of Cd, Co, Mn, Ni, and Zn in the tailings. The presence of aloes benefited germination rates, leaf count, length, and plant biomass of grasses and daisies in the mine tailings, without significant allelopathic effects. Therefore, aloes-especially A. castanea-should be employed in the rehabilitation of metal-contaminated soils to extract metals and to aid the establishment of other species to enhance the phytoremediation processes.