Quercus rubra invasion of temperate deciduous forest stands alters the structure and functions of the soil microbiome.

Invasive plants can modify the diversity and taxonomical structure of soil microbiomes. However, it is difficult to generalize the underlying factors as their influence often seems to depend on the complex plant-soil-microbial interactions. In this paper, we investigated how Quercus rubra impacts on the soil microbiome across two soil horizons in relation to native woodland. Five paired adjacent invaded vs native vegetation plots in a managed forest in southern Poland were investigated. Soil microbial communities were assessed along with soil enzyme activities and soil physicochemical parameters, separately for both organic and mineral horizons, as well as forest stand characteristics to explore plant-soil-microbe interactions. Although Q. rubra did not significantly affect pH, organic C, total N, available nutrients nor enzymatic activity, differences in soil abiotic properties (except C to N ratio) were primarily driven by soil depth for both vegetation types. Further, we found significant differences in soil microbiome under invasion in relation to native vegetation. Microbial richness and diversity were lower in both horizons of Q. rubra vs control plots. Moreover, Q. rubra increased relative abundance of unique amplicon sequence variants in both horizons and thereby significantly changed the structure of the core soil microbial communities, in comparison to the control plots. In addition, predicted microbial functional groups indicated a predominant soil depth effect in both vegetation plots with higher abundance of aerobic chemoheterotrophic bacteria and endophytic fungi in the organic horizon and greater abundance of methanotrophic and methylotrophic bacteria, and ectomycorrhizal fungi in the mineral horizon. Overall, our results indicate strong associations between Q. rubra invasion and changes in soil microbiome and associated functions, a finding that needs to be further investigated to predict modifications in ecosystem functioning caused by this invasive species.

Herbaceous plant species support soil microbial performance in deciduous temperate forests.

Although herbaceous plant layer may contribute significantly to plant diversity and nutrient turnover, its effects on the soil environment in forest ecosystems remain largely unexplored. In this study, we compared the effects of mono-dominant and multi-species assemblages of herb plants on soil physicochemical and microbial properties in two temperate deciduous (beech and riparian) forests. We hypothesized that the presence of herbaceous plants would increase microbial activity and biomass, and nutrient availability in soil when compared to bare soil. This increase would be the highest in multi-species assemblages as high plant diversity supports microbial performance and soil processes, and the expected patterns would be essentially similar in both forests. Allium ursinum L. and Dentaria enneaphyllos L. represented herb species forming mono-dominant patches in beech forest, while Aegopodium podagraria L. and Ficaria verna Huds. represented herb species forming mono-dominant patches in riparian forest. Our hypotheses were only partly supported by the data. We found that herb plant species affected soil microbial communities and processes, particularly in the riparian forest, but they generally did not influence soil physicochemical properties. In the beech forest, herbaceous plants increased saprotrophic fungi biomass, fungi/bacteria ratio, and arylsulfatase activity, with the highest values under D. enneaphyllos. In the riparian forest, a number of microbial parameters, namely bacteria, G+ bacteria, and saprotrophic fungi biomass, fungi/bacteria ratio, and soil respiration exhibited the lowest values in bare soil and the highest values in soil under A. podagraria. Contrary to expectations, soils under multi-species assemblages were characterized by intermediate values of microbial parameters. Concluding, herbaceous plant species largely supported soil microbial communities in deciduous temperate forests but did not affect soil chemical properties. The potential reasons for the positive influence of herb plants on soil microbes (litterfall, rhizodeposition) require further investigation.

Functional traits predict resident plant response to Reynoutria japonica invasion in riparian and fallow communities in southern Poland.

Reynoutria japonica is one of the most harmful invasive species in the world, dramatically reducing the diversity of resident vegetation. To mitigate the impact of R. japonica on ecosystems and properly manage affected areas, understanding the mechanisms behind this plant's invasive success is imperative. This study aimed to comprehensively analyse plant communities invaded by R. japonica, taking into account species traits, habitat conditions and seasonal variability, and to determine the ecological profile of species that withstand the invader's pressure. The study was performed in fallow and riparian areas in southern Poland. Pairs of adjacent plots were established at 25 sites with no obvious signs of recent human disturbance. One plot contained R. japonica, and the other contained only resident vegetation. For each plot, botanical data were collected and soil physicochemical properties were determined. Twelve sites were surveyed four times, in two springs and two summers, to capture seasonal variability. The presence of R. japonica was strongly associated with reduced resident plant species diversity and/or abundance. In addition to the ability to quickly grow and form a dense canopy that shades the ground, the success of the invader likely resulted from the production of large amounts of hard-to-decompose litter. The indirect impact of R. japonica by controlling the availability of nutrients in the soil might also play a role. A few species coexisted with R. japonica. They can be classified into three groups: (i) spring ephemerals - geophytic forbs with a mixed life history strategy, (ii) lianas with a competitive strategy and (iii) hemicryptophytic forbs with a competitive strategy. Species from the first two groups likely avoided competition for light by temporal or spatial niche separation (they grew earlier than or above the invasive plant), whereas the high competitive abilities of species from the third group likely enabled them to survive in R. japonica patches.

Invasive plant Reynoutria japonica produces large amounts of phenolic compounds and reduces the biomass but not activity of soil microbial communities.

Reynoutria japonica is one of the most invasive plant species. Its success in new habitats may be associated with the release of secondary metabolites. The aim of this study was to compare phenolic concentrations in plant biomass and soils between plots with R. japonica and resident plants (control), and determine the effects of these compounds on soil microbial communities. Samples of plant shoots and rhizomes/roots, and soil were collected from 25 paired plots in fallow and riparian habitats in Poland. We measured concentrations of total phenolics, condensed tannins, catechin, chlorogenic acid, emodin, epicatechin, hyperoside, physcion, piceatannol, polydatin, procyanidin B3, quercetin, resveratrol, and resveratroloside. Soil microbial parameters were represented by acid and alkaline phosphomonoesterases, ß-glucosidase, phenoloxidase, and peroxidase activity, culturable bacteria activity and functional diversity measured with Biolog Ecoplates, and microbial biomass and community structure measured with phospholipid fatty acid (PLFA) analysis. We found that concentrations of total phenolics and condensed tannins were very high in R. japonica leaves and rhizomes/roots, and concentrations of most phenolic compounds were very high in R. japonica rhizomes/roots when compared to resident plant species. Concentrations of most phenolics in mineral soil did not differ between R. japonica and control plots; the only exceptions were catechin and resveratrol which were higher and lower, respectively, under the invader. Total microbial and bacterial (G+, G-) biomass was decreased by approx. 30% and fungal biomass by approx. 25% in invaded soils in comparison to control. Among soil functional microbial parameters, only peroxidase activity and functional diversity differed between R. japonica and resident plant plots; peroxidase activity was higher, while functional diversity was lower in soil under R. japonica. The negative effects of R. japonica on microbial biomass may be related to catechin or its polymers (proanthocyanidins) or to other phenolics contained in high concentrations in R. japonica rhizomes.

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).

Invasive Quercus rubra negatively affected soil microbial communities relative to native Quercus robur in a semi-natural forest.

Invasive tree species can exert a profound effect on soil properties and ecosystem processes. Quercus rubra is a Northern American species that has an invader status in many European countries. However, the direction and magnitude of its effect on soil physicochemical and microbial properties relative to native tree species in forests are largely unknown. The aim of this study was to investigate the influence of invasive Q. rubra on physicochemical and microbial properties of soil organic and mineral horizons in comparison to native Quercus robur in a semi-natural forest. The study was performed on 23 Q. rubra and 10 Q. robur stands in the Niepolomice Forest (southern Poland). A number of soil parameters were assessed, namely moisture, water holding capacity, electrical conductivity, pH, organic C, total N, respiration, bacterial and fungal biomass and community structure (phospholipid fatty acid and ergosterol analyses). As soil properties are influenced by the quality of leaf litter deposited by trees, senesced Q. rubra and Q. robur leaves were characterized in terms of C, Ca, Mg, K, N, P, total phenolics and condensed tannins concentrations. It was found that total microbial and bacterial biomass was significantly lower under Q. rubra than Q. robur in both soil horizons. Microbial community structure of organic horizon also differed between the two Quercus species. In contrast, no differences were found in fungal biomass and soil physicochemical variables. The reduction in microbial and bacterial biomass beneath Q. rubra may be associated with the quantity and quality of its litter. Senesced Q. rubra leaves were characterized by significantly higher C/N and C/P ratios relative to those of Q. robur. Preliminary data indicate that although they had lower concentrations of phenolics and condensed tannins, the pools of these compounds supplied to the soil were higher due to higher litter production by Q. rubra.

Invasion of Rosa rugosa induced changes in soil nutrients and microbial communities of coastal sand dunes.

The aim of this study was to investigate the influence of R. rugosa invasion on soil physicochemical and microbial properties of coastal sand dunes. The study was performed at 25 paired invaded-native plots along the Hel Peninsula at the coast of the Baltic Sea. A number of soil physicochemical and microbial parameters were measured, namely organic matter layer thickness, pH, electrical conductivity, organic C, total Ca, N, Na, P, N-NH4, N-NO3 and P-PO4 concentrations, phospholipid and neutral fatty acid (PLFA, NLFA) markers of total microbial, bacterial, fungal biomass and microbial community structure, as well as arbuscular mycorrhizal fungi (AMF) spore and species numbers, and the degree of AMF root colonization. Since potential alterations in soil parameters induced by R. rugosa may be related to large amounts of secondary metabolites provided to the soil with litter or root exudates, total phenolic concentration in senescing tissues of R. rugosa and native species was compared. Rosa rugosa invasion was associated with increased organic C, total N and P-PO4 concentrations in mineral soil relative to native vegetation. Organic matter layer under R. rugosa was thicker, had higher pH and Ca concentration. Rosa rugosa invasion was associated with reduced total microbial, bacterial and G+ bacterial biomass and increased AMF biomass markers (16:1ω5 NLFA and 16:1ω5 NLFA/PLFA), and changes in microbial community structure in mineral soil. The reduction in total and bacterial biomass under R. rugosa might have been related to the production of secondary metabolites as total phenolic concentration was approx. 5 times higher in senescing tissues of R. rugosa than in native vegetation. The observed increase in element concentrations and alterations in microbial community structure suggest that invasion of R. rugosa may threaten nutrient-poor habitats of coastal dunes. Changes in the soil environment may hinder restoration of these valuable habitats after invader removal.

Relationships between waste physicochemical properties, microbial activity and vegetation at coal ash and sludge disposal sites.

The aim of the study was to assess the relationships between vegetation, physicochemical and microbial properties of substrate at coal ash and sludge disposal sites. The study was performed on 32 plots classified into 7 categories: dried ash sedimentation ponds, dominated by a grass Calamagrostis epigejos (AH-Ce), with the admixture of Pinus sylvestris (AH-CePs) or Robinia pseudoacacia (AH-CeRp), dry ash landfill dominated by Betula pendula and Pinus sylvestris (AD-BpPs) or Salix viminalis (AD-Sv) and coal sludge pond with drier parts dominated by Tussilago farfara (CS-Tf) and the wetter ones by Cyperus flavescens (CS-Cf). Ash sites were covered with soil layer imported as a part of technical reclamation. Ash had relatively high concentrations of some alkali and alkaline earth metals, Mn and pH, while coal sludge had high water and C, S, P and K contents. Concentrations of heavy metals were lower than allowable limits in all substrate types. Microbial biomass and, particularly, enzymatic activity in ash and sludge were generally low. The only exception were CS-Tf plots characterized by the highest microbial biomass, presumably due to large deposits of organic matter that became available for aerobic microbial biomass when water level fell. The properties of ash and sludge adversely affected microbial biomass and enzymatic activity as indicated by significant negative correlations between the content of alkali/alkaline earth metals, heavy metals, and macronutrients with enzymatic activity and/or microbial biomass, as well as positive correlations of these parameters with metabolic quotient (qCO2). Plant species richness and cover were relatively high, which may be partly associated with alleviating influence of soil covering the ash. The effect of the admixture of R. pseudoacacia or P. sylvestris to stands dominated by C. epigejos was smaller than expected. The former species increased NNH4, NNO3 and arylsulfatase activity, while the latter reduced activity of the enzyme.

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.

Few effects of invasive plants Reynoutria japonica, Rudbeckia laciniata and Solidago gigantea on soil physical and chemical properties.

Biological invasions are an important problem of human-induced changes at a global scale. Invasive plants can modify soil nutrient pools and element cycling, creating feedbacks that potentially stabilize current or accelerate further invasion, and prevent re-establishment of native species. The aim of this study was to compare the effects of Reynoutria japonica, Rudbeckia laciniata and Solidago gigantea, invading non-forest areas located within or outside river valleys, on soil physical and chemical parameters, including soil moisture, element concentrations, organic matter content and pH. Additionally, invasion effects on plant species number and total plant cover were assessed. The concentrations of elements in shoots and roots of invasive and native plants were also measured. Split-plot ANOVA revealed that the invasions significantly reduced plant species number, but did not affect most soil physical and chemical properties. The invasions decreased total P concentration and increased N-NO3 concentration in soil in comparison to native vegetation, though the latter only in the case of R. japonica. The influence of invasion on soil properties did not depend on location (within- or outside valleys). The lack of invasion effects on most soil properties does not necessarily imply the lack of influence of invasive plants, but may suggest that the direction of the changes varies among replicate sites and there are no general patterns of invasion-induced alterations for these parameters. Tissue element concentrations, with the exception of Mg, did not differ between invasive and native plants, and were not related to soil element concentrations.

Variation in dry grassland communities along a heavy metals gradient.

The aim of this study was to investigate the variation in plant communities growing on metal-enriched sites created by historical Zn­Pb mining. The study sites were 65 small heaps of waste rock covered by grassland vegetation and scattered mostly over agricultural land of southern Poland. The sites were described in terms of plant coverage, species richness and composition, and the composition of plant traits. They were classified using phytosociological methods and detrended correspondence analysis. Identified plant communities were compared for vegetation parameters and habitat properties (soil characteristics, distance from the forest) by analysis of variance. The variation in plant community parameters was explained by multiple regression, in which the predictors were properties of the habitat selected on the basis of factor analysis. Grasslands that developed at low and high concentrations of heavy metals in soil were similar to some extent: they were composed on average of 17­20 species (per 4 m(2)), and their total coverage exceeded 90%. The species composition changed substantially with increasing contamination with heavy metals; metal-sensitive species withdrew, while the metal-tolerant became more abundant. Other important predictors of community structure were: proximity to the forest (responsible for the encroachment of competitive forest species and ruderals), and the thickness of the surface soil (shallow soil favored the formation of the heavy metal grassland). The heavy metal grassland was closely related to the dry calcareous grasslands. The former was an earlier succession stage of the latter at low contamination with heavy metals.

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.

Soil fertility and plant diversity enhance microbial performance in metal-polluted soils.

This study examined the effects of soil physicochemical properties (including heavy metal pollution) and vegetation parameters on soil basal respiration, microbial biomass, and the activity and functional richness of culturable soil bacteria and fungi. In a zinc and lead mining area (S Poland), 49 sites were selected to represent all common plant communities and comprise the area's diverse soil types. Numerous variables describing habitat properties were reduced by PCA to 7 independent factors, mainly representing subsoil type (metal-rich mining waste vs. sand), soil fertility (exchangeable Ca, Mg and K, total C and N, organic C), plant species richness, phosphorus content, water-soluble heavy metals (Zn, Cd and Pb), clay content and plant functional diversity (based on graminoids, legumes and non-leguminous forbs). Multiple regression analysis including these factors explained much of the variation in most microbial parameters; in the case of microbial respiration and biomass, it was 86% and 71%, respectively. The activity of soil microbes was positively affected mainly by soil fertility and, apparently, by the presence of mining waste in the subsoil. The mining waste contained vast amounts of trace metals (total Zn, Cd and Pb), but it promoted microbial performance due to its inherently high content of macronutrients (total Ca, Mg, K and C). Plant species richness had a relatively strong positive effect on all microbial parameters, except for the fungal component. In contrast, plant functional diversity was practically negligible in its effect on microbes. Other explanatory variables had only a minor positive effect (clay content) or no significant influence (phosphorus content) on microbial communities. The main conclusion from this study is that high nutrient availability and plant species richness positively affected the soil microbes and that this apparently counteracted the toxic effects of metal contamination.

Direct and indirect effects of metal contamination on soil biota in a Zn-Pb post-mining and smelting area (S Poland).

Effects of metal contamination on soil biota activity were investigated at 43 sites in 5 different habitats (defined by substratum and vegetation type) in a post-mining area. Sites were characterised in terms of soil pH and texture, nutrient status, total and exchangeable metal concentrations, as well as plant species richness and cover, abundances of enchytraeids, nematodes and tardigrades, and microbial respiration and biomass. The concentrations of total trace metals were highest in soils developed on mining waste (metal-rich dolomite), but these habitats were more attractive than sandy sites for plants and soil biota because of their higher content of organic matter, clay and nutrients. Soil mesofauna and microbes were strongly dependent on natural habitat properties. Pollution (exchangeable Zn and Cd) negatively affected only enchytraeid density; due to a positive relationship between enchytraeids and microbes it indirectly reduced microbial activity.

Pine forest and grassland differently influence the response of soil microbial communities to metal contamination.

Metal pollution can affect soil microbial communities, and vegetation potentially influences this relationship. It can, for example, modify the toxicity of metal to soil microbes by controlling its input to the ground or by altering soil physicochemical properties. This study examined metal effects on soil respiration, potentially active microbial biomass (SIR) and catabolic abilities of culturable heterotrophic bacterial communities (Biolog GN) in pine forest and grassland ecosystems developed on soils contaminated with Zn, Pb and Cd. In samples from non-forested areas we found that metal pollution reduced the microbial biomass and functional diversity of bacteria, while increasing the metabolic quotient. In samples from pine forests we found no relationship between metal pollution and microbial parameters. Metals induced changes in soil respiration neither in forest nor in grassland sites. Generally, microbial performance was determined predominantly by soil physicochemical properties (nutrient content, acidity, contamination level). Vegetation type seemed a minor but important factor influencing microbial communities. More work is needed to determine why even relatively high metal concentrations do not significantly affect microbial communities in forest soils.

Model-based experimental design for assessing effects of mixtures of chemicals.

We exposed flour beetles (Tribolium castaneum) to a mixture of four poly aromatic hydrocarbons (PAHs). The experimental setup was chosen such that the emphasis was on assessing partial effects. We interpreted the effects of the mixture by a process-based model, with a threshold concentration for effects on survival. The behavior of the threshold concentration was one of the key features of this research. We showed that the threshold concentration is shared by toxicants with the same mode of action, which gives a mechanistic explanation for the observation that toxic effects in mixtures may occur in concentration ranges where the individual components do not show effects. Our approach gives reliable predictions of partial effects on survival and allows for a reduction of experimental effort in assessing effects of mixtures, extrapolations to other mixtures, other points in time, or in a wider perspective to other organisms.

Metals affect soil bacterial and fungal functional diversity differently.

Heavy metals can cause a decrease in the taxonomic diversity of soil communities. Because of functional redundancy, it remains unclear to what extent different functions performed by the soil microbial communities may be affected by pollution. We studied the impact of metal contamination on soil bacterial and fungal functional diversity, active microbial biomass, and soil respiration rate. Soil samples were collected from 39 sites along three forest and five meadow pollution transects near an abandoned Pb/Zn smelter in Avonmouth (UK) and Ni smelter in Clydach (UK), in a Cu mining and smelting region near Glogów (Poland), and in a Zn/Pb mining and smelting region near Olkusz (Poland). Biolog GN2 and SFN2 plates were used to study the bacterial and fungal functional diversity, which subsequently was expressed as Shannon's diversity index (H'). The active microbial biomass was measured as substrate-induced respiration. We found that the bacterial functional diversity significantly decreased, whereas the fungal functional diversity slightly increased, with increasing metal concentration. We also observed a slight negative effect of metal pollution on the active microbial biomass. No relationship was found between metal contamination and total soil respiration rate. This suggests a higher sensitivity of bacterial functional diversity as an indicator for the effects of metal pollution compared with overall soil respiration. All microbial parameters were affected by nutrient concentrations and/or soil pH.