Variation in dry grassland communities along a heavy metals gradient

Microplastics and cadmium affect invasion success by altering complementarity and selection effects in native community

The diversity-invasibility hypothesis predicts that native plant communities with high biodiversity should be more resistant to invasion than low biodiversity communities. However, observational studies have found that there is often a positive relationship between native community diversity and invasibility. Pollutants were not tested for their potential to cause this positive relationship. Here, we established native communities with three levels of diversity (1, 2 and 4 species) and introduced an invasive plant [Symphyotrichum subulatum (Michx.) G. L. Nesom] to test the effects of different pollutant treatments (i.e., unpolluted control, microplastics (MPs) alone, cadmium (Cd) alone, and their combination) on the relationship between native community diversity and community invasibility. Our results indicate that different MPs and Cd treatments altered the invasibility of native communities, but this effect may depend on the type of pollutant. MPs single treatment reduced invasion success, and the degree of reduction increased with increasing native community diversity (Diversity 2: - 14.1 %; Diversity 4: - 63.1 %). Cd single treatment increased the aboveground biomass of invasive plants (+ 40.2 %) and invasion success. The presence of MPs inhibited the contribution of Cd to invasion success. Furthermore, we found that the complementarity and selection effects of the native community were negatively correlated with invasion success, and their relative contributions to invasion success also depended on the pollutant type. We found new evidence of how pollutants affect the relationship between native community diversity and habitat invasibility, which provides new perspectives for understanding and managing biological invasions in the context of environmental pollution. This may contribute to promoting the conservation of biodiversity, especially in ecologically sensitive and polluted areas.

Diversity and botanical composition of native species in the Pampa biome in vineyards cultivated on soils with high levels of copper, zinc and manganese and phytoremediation potential

Viticulture allows the preservation of native species inside vineyards in the Pampa biome. However, phytosanitary treatments in these areas can increase the levels of Cu, Zn and Mn. The study aimed to (i) verify the influence of Cu, Zn and Mn contents in Pampa biome soils; (ii) identify variables related to Cu, Zn and Mn that most contribute to the variation in richness, diversity, and dry matter production of native vegetation, (iii) investigate the phytoremediation potential of species present in vineyards. Botanical composition, Cu, Zn, Mn available in the soil, and plant nutritional composition in two vineyards (V1 and V2) and native field (NF) were evaluated. Vineyards showed higher Cu, Zn and Mn contents in the soil, resulting in the lowest biomass, richness, and diversity of native species. Mn in tissue was the most important variable in explaining the variation in dry matter. Zn in the soil helped to explain the difference in species richness and diversity. P concentration in tissue was important in elucidating the variation in species diversity. Paspalum plicatulum and Paspalum notatum have potential for phytostabilization of metals in vineyards.

Woody plants have the advantages in the phytoremediation process of manganese ore with the help of microorganisms

The serious ecological damage caused by mining activities cannot be ignored. The use of an environmentally friendly restoration method to rebuild the vegetation and soil environment in the mining area has attracted more and more attention. This paper aims to study soil quality as well as vegetation characteristics of four woody species including Pinus massoniana (P. massoniana), Broussonetia papyrifera (B. papyrifera), Koelreuteria paniculata (K. paniculata), Osmanthus fragrans (O. fragrans), and two herbaceous species including Setaria viridis (S. viridis) and Cynodon dactylon (C. dactylon). In addition, we further clarified the effects of B. papyrifera and K. paniculata on soil nutrients and microbial communities after restoration. The results showed that the vegetation restoration area had better soil quality and plant community diversity, and the woody plants restoration effect were better. Compared with slag, B. papyrifera and K. paniculata remediation could improve soil pH and mitigate heavy metal contamination in mining areas, but was not effective in enhancing Soil Organic Matter (SOM), Total Nitrogen (TN), Total Potassium (TK) and Total Phosphorus (TP). In addition, the abundance and diversity of soil bacterial communities were increased. Of all the study sites, Proteobacteria had the greatest dominance. Vegetation restoration resulted in an increase in the relative abundance of Acidobacteria, while a decrease in Actinobacteria, Cyanobacteria and Firmicutes. With the restoration of vegetation, the increase of pH, the change of TN, SOM, TK, TP and the mitigation of Manganese (Mn) pollution were the main reasons affecting the soil microbial community. This study has great significance for understanding the ecological changes in the mining area after artificially mediated vegetation restoration, including changes in soil environment, plant community and microbial community, and woody plants will be more encouraged for the restoration of manganese mining areas.

Site-specific ecological effect assessment at community level for polymetallic contaminated soil

Current ecological risk assessment (ERA) is based more on book-keeping than on science especially for terrestrial ecosystems due to the lack of relevance to real field. Accordingly, site-specific ecological effect assessment is critical for ERA, especially at high tiers. This study developed procedures to assess ecological effect at community level based on field data. As a case study, we assessed ecological effect of polymetallic contamination in soil in the surrounding of an abandoned mining and smelting site in Hunan, China. Firstly, Zn was identified as the dominant contaminant in soil and slope gradient (SG) and pH as environmental impact factors using distance-based redundancy analysis(db-RDA). Secondly, sensitive endpoints were screened using correlation analysis between Zn and parameters of plant community composition and functional traits. Thirdly, exposure-effect curves between Zn and screened endpoints were developed by taking SG and pH as covariates using Bayesian kernel machine regression analysis (BKMR), based on which half-effect concentrations (EC₅₀s) and 10 %-effect concentrations (EC₁₀s) of soil Zn for each endpoint were calculated. Finally, site-specific hazardous concentrations (HC₅₀s) of Zn were estimated. It was revealed site-specific EC₅₀s and EC₁₀s for soil Zn ranged 80.5-201 mg kg^-1 and 342-893 mgkg^-1, respectively, and HC₅₀s based on EC₁₀s and EC₅₀s ranged 104-110 mg kg^-1 and 595-612 mg kg^-1, respectively, which are more specific and inclusive than those obtained based on crop and vegetable seed germination and seedling growth toxicity experiments.

Mapping leaf metal content over industrial brownfields using airborne hyperspectral imaging and optimized vegetation indices

Monitoring plant metal uptake is essential for assessing the ecological risks of contaminated sites. While traditional techniques used to achieve this are destructive, Visible Near-Infrared (VNIR) reflectance spectroscopy represents a good alternative to monitor pollution remotely. Based on previous work, this study proposes a methodology for mapping the content of several metals in leaves (Cr, Cu, Ni and Zn) under realistic field conditions and from airborne imaging. For this purpose, the reflectance of Rubus fruticosus L., a pioneer species of industrial brownfields, was linked to leaf metal contents using optimized normalized vegetation indices. High correlations were found between the vegetation indices exploiting pigment-related wavelengths and leaf metal contents (r ≤ - 0.76 for Cr, Cu and Ni, and r ≥ 0.87 for Zn). This allowed predicting the metal contents with good accuracy in the field and on the image, especially Cu and Zn (r ≥ 0.84 and RPD ≥ 2.06). The same indices were applied over the entire study site to map the metal contents at very high spatial resolution. This study demonstrates the potential of remote sensing for assessing metal uptake by plants, opening perspectives of application in risk assessment and phytoextraction monitoring in the context of trace metal pollution.

Phosphorus is more effective than nitrogen in restoring plant communities of heavy metals polluted soils

Heavy metal pollution is widespread, and has an increasing trend in some countries and regions. It can be easily accumulated in plants, leading to plant species loss and affecting plant community composition. Artificial restoration can conserve plant diversity in contaminated soils and accelerate the recovery of polluted ecosystems. The application of nitrogen (N) and phosphorus (P) is inexpensive and convenient, which can increase the resistance of plants to adversity and promote the growth of plants in heavy metal polluted soils. In order to examine the effect of N and P nutrition on the conservation of plant community, we conducted a comparison experiment in greenhouse using soil with low N and P concentration, and set five treatments: C (soil with no heavy metals and fertilizer addition), H (soil with heavy metals addition but with no fertilizer), HN (soil with heavy metals and N addition), HP treatment(soil with heavy metals and P addition), HNP treatment (soil with heavy metals, N and P addition). Our results showed that heavy metal pollution reduced plant species by 300%, and significantly decreased plant diversity (P < 0.05). N addition increased the richness of plant species and increased the dominance of Euphorbia peplus, but had no significant effect on plant diversity and community structure, while reduced the evenness of plant species. P addition of HP and HNP treatments restored plant species richness and increased plant diversity under heavy metal pollution. The plant community structures of these two treatments were more similar to that of group C. Compared with N addition, P addition had a better performance to restoring the species composition and relative dominance of plant communities. Our results provided a guidance for the restoration of plant communities and the conservation of plant species in low N and P concentration soils with the context of heavy metal pollution.

Spatial variation of herbaceous cover species community in Cu-contaminated vineyards in Pampa biome

Study's objective was to evaluate spatial variability of herbaceous cover species community in vineyards cultivated in soil with increasing Cu levels in Pampa biome. Three vineyards, with increasing soil Cu available contents and a natural field area (NF), were selected. In each experimental area, soil Cu content, botanical composition, cumulative aerial biomass, and aerial part Cu concentration, in most frequent species, were evaluated. In total, 39 vascular plant species were identified, including four exotic species. Biodiversity indicators did not significantly correlate with soil Cu. However, botanical composition variation could be observed. In NF, Poaceae and Asteraceae families presented greater dry mass contribution, while this contribution decreased in higher soil Cu concentration areas. The Cu concentration and accumulation in plant aerial part were higher in older vineyards, as plant aerial part accumulated, in average, 13.8 mg Cu m^-2. Among species found in experimental fields, Ageratum conyzoides, a species known to form Cu-tolerant populations, occurred in most areas, especially in vineyards, presenting higher aerial Cu concentrations, with a mean of 126.47 mg kg^-1. Soil enrichment with Cu did not alter the vegetation's biodiversity, but may have contributed to the botanical composition modification. The native species, P. plicatulum and A. conyzoides, presented a high bio-accumulation factor and are potential candidates for phytoremediation techniques.

Soil organic matter prevails over heavy metal pollution and vegetation as a factor shaping soil microbial communities at historical Zn-Pb mining sites

This study examined the effects of soil heavy metals, macronutrients, texture and pH as well as plant species richness and composition on soil respiration, enzymatic activity, microbial biomass, metabolic quotient (qCO₂) and arbuscular mycorrhizal fungi (AMF) at sites of historical Zn-Pb mining. The study was conducted both on a large scale (65 heaps scattered over the area of 750 km²) and on a small scale (25 plots along two 48 m transects extending from heaps to adjacent fallow fields). Total concentrations of metals exceeded 400 (Cd), 20,000 (Pb) and 80,000 (Zn) mg kg^-1 at the most polluted sites. Although they decreased along the heap-fallow direction, they still remained above environmental standards in fallow soils. In contrast, some soluble metal forms increased with the increasing distance from heaps. Soil organic matter had the strongest positive effect on most microbial parameters. Total and/or available heavy metals exhibited significant negative effects on microbial biomass, enzymatic activity and AMF, and a positive effect on qCO₂. Organic matter alleviated negative effects of heavy metals on microorganisms; they were not observed where the increase in the contamination was accompanied by the increase in organic matter content. Plant species richness affected positively enzymatic activity and mycorrhization level. Plant species composition possibly contributed to the formation of soil microbial communities, but its effect was entangled in that of heavy metals as plant communities changed along pollution gradients (from metal-tolerant grasslands dominated by Festuca ovina to calcareous grasslands and ruderal communities at less polluted sites).

Metal contamination of river otters in North Carolina

Aquatic apex predators are vulnerable to environmental contaminants due to biomagnification. North American river otter (Lontra canadensis) populations should be closely monitored across their range due to point and nonpoint pollution sources. Nonetheless, no information exists on environmental contaminants in the North Carolina otter population. Metals and metalloids occur naturally across the landscape, are essential for cellular function, and become toxic when concentrated unnaturally. We conducted our study across the three Furbearer Management Units (FMU) and 14 river basins of North Carolina. We determined the concentrations of arsenic, cadmium, calcium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, selenium, thallium, and zinc in liver and kidney samples from 317 otters harvested from 2009 to 2016. Arsenic, lead, and thallium samples were tested at levels below the limit of detection. With the exception of cadmium, we detected all other elements at higher levels in the liver compared with the kidney. Specifically, cadmium, cobalt, copper, iron, magnesium, manganese, mercury, molybdenum, and zinc levels differed by tissue type analyzed. Most element concentrations remained stable or increased with otter age. We detected higher levels of mercury and selenium in the Lower Pee Dee and Cape Fear river basins. River basins within the Mountain FMU were higher in cadmium, copper, iron, lead, and zinc, whereas the Coastal Plain FMU was lower in cobalt and manganese. None of the elements occurred at toxic levels. Our research establishes baseline concentration levels for North Carolina, which will benefit future monitoring efforts and provide insight into future changes in the otter population.

Effects of manganese stress on phenology and biomass allocation in Xanthium strumarium from metalliferous and non-metalliferous sites

Xanthium strumarium is an annual pseudometallophyte. To reveal the mechanisms of this species to adapt to metallicolous environmental conditions, phenological traits and biomass allocation of metallicolous and non-metallicolous populations of X. strumarium under six Mn²⁺ concentrations by pot culture experiments were performed. The results showed that both time to bolting and time to fruit setting in the metallicolous population were earlier than those in the non-metallicolous population. The number of flowers, fruits, seeds and 1000-seed weight in the metallicolous population were higher than those in the non-metallicolous population under Mn stress. Reproductive allocation and harvest index in the metallicolous population were higher than those in the non-metallicolous population. Furthermore, all the Mn concentrations in leaves, stems, roots, and fruits of the metallicolous population were higher than the counterparts of non-metallicolous population. These results suggested that metallicolous population had higher tolerance to Mn stress than non-metallicolous population, the earlier flowering and fruiting, and the enhancement in reproductive allocation may contribute to plant tolerance to Mn toxicity for X. strumarium.

The succession of the plant community on a decontaminated radioactive meadow site

Long-term observation of the succession in a plant community is considered a fundamental unit used to investigate the expected consequences of soil contamination by radionuclides and to understand restoration of technogeneously disturbed ecosystems. The development of arboreal willow meadow under remediation of a radioactively contaminated site has been studied for half a century. Succession stages in the formation of the de novo community were noted. Changes in the floristic composition, soil structure as well as radionuclide activity concentrations in topsoil were registered on each step. Technical recultivation of the area including covering radioactive wastes with a mixture of sand and gravel led to lower the radiation levels and was suitable for decontamination during first 5-8 years. This allowed the community to develop with maximal effectiveness on the initial steps. Than the covering layer lost its barrier functions but no adverse effects at dose rates up to 150 μGy/h on completion of the community formation were registered. Radioecological conditions and changes in the plant community development were registered simultaneously on the area studied that makes possible to follow main doseforming radionuclides migration and to determine main steps of the succession. The study results is a practical demonstration that edaphic niches, climatic conditions and сoenotic relationships between plants play a more important role in the evolution of the studied community than the contamination type and radiation exposure levels.

Factors of variation in beech forest understory communities on waste heaps left by historical Zn-Pb ore mining

The species trait-environment relationships in understory vegetation were carried out on metalliferous sites created by historical Zn-Pb mining (S Poland), on which natural revegetation took place. The study sites were 31 small heaps of waste rock covered by an 80-120 year old beech forest. The sites were described in terms of plant coverage, species richness and composition, and the composition of plant traits. Three types of understory communities that were identified were compared for environmental variables and plant parameters. Despite a high concentration of heavy metals in soils, namely Cd, Pb, and Zn, the degree of shading by the tree canopy was the main factor determining variation in understory communities. The understories that developed in low and strong shading were similar to some extent: They had high number of species, and they were characterized by a high proportion of the ancient forest species. The species composition changed substantially with increasing coverage of trees; mixed strategy plants withdrew, while the stress tolerant species became more abundant. The other predictor of community structure was the ratio of Cd to Ca, which was responsible for the decrease of woody plants and the endangered species. This study proved that, in the case of highly complex and productive ecosystems, even with a high degree of contamination with heavy metals, the biotic factors play a primary role.

Restoration of Vegetation in Relation to Soil Properties of Spoil Heap Heavily Contaminated with Heavy Metals

The main objectives of our study were to evaluate soil contamination on a zinc-lead spoil heap in the Upper Silesian Industrial Region in southern Poland using pollution indices, and to investigate the relation between soil properties and the natural succession of vegetation. Organic carbon and nitrogen, pH, soil texture, base cations, and heavy metal content were analyzed in soil samples at depths of 0-15 cm below the organic horizon over a regular grid of 14 sampling plots. The contents of Zn, Pb, and Cd exceeded by several times the acceptable thresholds. Measurements of soil enzyme activity were used to evaluate the progress of vegetation development in relation to soil chemical properties. The results indicate that heavy metals had a significant impact on soil enzyme activity and the development of vegetation cover. High contents of Pb and Cd reduced enzyme activity, while this activity increased with increasing amounts of soil organic matter. Further, the accumulative capacities of heavy metals in needles of Scots pine (Pinus sylvestris L.) and aboveground biomass of bladder campion (Silene vulgaris (Moench) Garcke) were examined. A high accumulation of Zn, Pb, and Cd in the aboveground tissues of S. vulgaris indicated an unusual tolerance of this species to heavy metals and the possibility of using this species in phytoremediation of post-industrial sites.

Differential Tolerance to Lead and Cadmium of Micropropagated Gypsophila fastigiata Ecotype

In vitro techniques may provide a suitable tool for effective propagation and conservation of plant species representing various ecological niches. The elaboration of such protocols is also prerequisite for selection of heavy-metal-tolerant plant material that could be afterwards used for restoration or remediation of polluted sites. In this study, culture protocol for Gypsophila fastigiata propagation was developed. The highest multiplication coefficient, which reached 6.5, and the best growth parameters were obtained on modified MS medium supplemented with 1.0 mg L-1 2iP and 0.2 mg L-1 IAA. The obtained cultures were treated with different concentrations of lead nitrate (0.1, 0.5, and 1.0 mM Pb(NO3)2) or cadmium chloride (0.5, 2.5, and 5.0 μM CdCl2). The growth parameters, photosynthetic pigments, and phenolic compound content were examined in order to evaluate whether tested metal salts can have an adverse impact on studied culture. It was ascertained that Pb ions induced growth disturbances and contributed to shoot wither. On the contrary, the proliferative shoot cultures were established on media containing Cd ions and the multiplication coefficients and shoot length increased on all media enriched with CdCl2. Chlorophylls and carotenoid contents were negatively affected by application of 5.0 μM of cadmium; nevertheless, in shoots treated with 2.5 μM CdCl2, increased accumulation of photosynthetic pigments occurred and their amount was similar to untreated culture. Adaptation to Cd was associated with stimulation of phenolic compound synthesis. Hence, we have reported on unambiguous positive result of in vitro selection procedure to obtain vigorous shoot culture tolerant to cadmium.

Waste heaps left by historical Zn-Pb ore mining are hotspots of species diversity of beech forest understory vegetation

Metalliferous mining and smelting industries are associated with very high levels of heavy metal(loid) contamination of the environment. Heavy metals have been proved to significantly influence the species diversity and composition of grassland communities, but little is known on their effects on forest understory vegetation. Therefore, the aim of this study was to investigate the effects of the presence of small heaps of waste rock left by historical Zn-Pb ore mining on understory vegetation. The heaps are scattered over vast areas of beech forests in southern Poland. Three types of study plots were established: (1) on waste heaps themselves, (2) in their vicinity (5-10m from the foot of the heaps, with no waste rock but potentially influenced by the heaps through drainage water), and (3) at least 100m from the foot of the heaps (pseudo-control). In all plots vegetation parameters, i.e., plant species number, cover and community composition, life forms and strategies, as well as basic soil properties were assessed. Although the heaps contained high concentrations of metals, namely Cd, Pb and Zn, they were characterised by higher cover and diversity of understory vegetation, including ancient forest and endangered species, in comparison to their surroundings. They were also characterised by the distinct species composition of their plant communities. This might have resulted from the beneficial influence of high pH and Ca content originating from waste rock composed of dolomite and calcite, as well as from increased habitat heterogeneity, e.g. soil skeleton and steeper slopes. Another important factor influencing the richness and composition of understory was tree cover, which relates to the light transmissibility of the canopy. Our study proved that the disturbance brought about by the former mining and processing of metal ores led to the formation of species-rich understory with high frequency and cover of naturally-valuable species.

The accumulation of elements in plants growing spontaneously on small heaps left by the historical Zn-Pb ore mining

The study evaluated the levels of nine metals, namely Ca, Cd, Fe, K, Mg, Mn, Pb, Tl, and Zn, in soils and tissues of ten plant species growing spontaneously on heaps left by historical mining for Zn-Pb ores. The concentrations of Cd, Pb, Tl, and Zn in heap soils were much higher than in control soils. Plants growing on heaps accumulated excessive amounts of these elements in tissues, on average 1.3-52 mg Cd kg(-1), 9.4-254 mg Pb kg(-1), 0.06-23 mg Tl kg(-1) and 134-1479 mg Zn kg(-1) in comparison to 0.5-1.1 mg Cd kg(-1), 2.1-11 mg Pb kg(-1), 0.02-0.06 mg Tl kg(-1), and 23-124 mg Zn kg(-1) in control plants. The highest concentrations of Cd, Pb, and Zn were found in the roots of Euphorbia cyparissias, Fragaria vesca, and Potentilla arenaria, and Tl in Plantago lanceolata. Many species growing on heaps were enriched in K and Mg, and depleted in Ca, Fe, and Mn. The concentrations of all elements in plant tissues were dependent on species, organ (root vs. shoot), and species-organ interactions. Average concentrations of Ca, K, and Mg were generally higher in shoots than in roots or similar in the two organs, whereas Cd, Fe, Pb, Tl, and Zn were accumulated predominantly in the roots. Our results imply that heaps left by historical mining for Zn-Pb ores may pose a potential threat to the environment and human health.