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Soil microbes play a key role in controlling ecosystem functions and providing ecosystem services. Yet, microbial communities in urban green space soils remain poorly characterized. Here we compared soil microbial communities in 41 urban parks of (i) divergent plant functional types (evergreen trees, deciduous trees, lawn) and (ii) different ages (constructed 10, ∼50, and >100 years ago). These microbial communities were also compared to those in 5 control forests in southern Finland. Our results indicate that, despite frequent disturbances in urban parks, urban soil microbes still followed the classic patterns typical of plant-microbe associations in natural environments: both bacterial and fungal communities in urban parks responded to plant functional groups, but fungi were under tighter control of plants than bacteria. We show that park age shaped the composition of microbial communities, possibly because vegetation in old parks have had a longer time to modify soil properties and microbial communities than in young parks. Furthermore, control forests harbored distinct but less diverse soil microbial communities than urban parks that are under continuous anthropogenic disturbance. Our results highlight the importance of maintaining a diverse portfolio of urban green spaces and plant communities therein to facilitate complex microbial communities and functions in urban systems. This article is protected by copyright. All rights reserved.

No-till is considered an agricultural practice beneficial for the environment as soil erosion is decreased compared to ploughed soils. For on overall evaluation of the benefits and disadvantages of this crop production method, understanding the soil nutrient cycle is also of importance. The study was designed to obtain information about gross soil nitrogen (N) process rates in boreal no-tilled and mouldboard ploughed spring barley (Hordeum vulgare L.) fields after autumn harvesting. In situ soil gross N transformation process rates were quantified for the 5 cm topsoil in 9 days’ incubation experiment using 15N pool dilution and tracing techniques and a numerical 15N tracing model. Gross N mineralization into ammonium (NH4 +) and NH4 + immobilization were the most important N transformation processes in the soils. The gross mineralization rate was 14% and NH4 + immobilization rate 64% higher in no-till than in ploughing. Regardless of the faster mineralization, the gross rate of NH4 + oxidation into nitrate (NO3 −) in no-till was one order of magnitude lower compared the ploughing. The results indicate that the no-tilled soils have the potential to decrease the risk for NO3 − leaching due to slower NH4 + oxidation.

The Grain for Green (GFG) Project in China is currently the largest environmental rehabilitation project aimed at turning low-yielding farm land to forests and pastures. Such conversion of land use type also promotes remediation of the polluted environment. Soil microbes reflect soil function and are therefore considered an essential component of ecosystem restoration. To evaluate the environmental effects of converting atrazine polluted farmland to secondary forest, we determined soil chemical properties, soil bacterial communities and their responses to three types of land use (primary forest, PF; secondary forest, SF; farm land, FL) in Wuying, China. Our results showed that soil organic matter significantly decreases in the order PF > SF > FL. Bacterial 16S rRNA gene 454 pyrosequencing revealed that the soil bacterial diversity level remained unchanged. However between FL and the two forested sites, we observed an increase of Actinobacteria, β-proteobacteria and Firmicutes; and a decrease of Acidobacteria and Verrucomicrobia, while in SF the bacterial community structure was similar to PF. We conclude that reforestation permits bacterial community, resetting from FL back to a state that resembles natural conditions. In addition, 20 years of natural attenuation degraded soil atrazine residues in SF but traces remained in the soil. Reforestation generally resulted in favorable ecological impacts on soil quality and the bacterial community compared with active farm fields.

Long-term exposure to polyaromatic hydrocarbons (PAHs) has been connected to chronic human health disorders. It is also well-known that i) PAH contamination alters soil bacterial communities, ii) human microbiome is associated with environmental microbiome, and iii) alteration in the abundance of members in several bacterial phyla is associated with adverse or beneficial human health effects. We hypothesized that soil pollution by PAHs altered soil bacterial communities that had known associations with human health. The rationale behind our study was to increase understanding and potentially facilitate reconsidering factors that lead to health disorders in areas characterized by PAH contamination. Large containers filled with either spruce forest soil, pine forest soil, peat, or glacial sand were left to incubate or contaminated with creosote. Biological degradation of PAHs was monitored using GC-MS, and the bacterial community composition was analyzed using 454 pyrosequencing. Proteobacteria had higher and Actinobacteria and Bacteroidetes had lower relative abundance in creosote contaminated soils than in non-contaminated soils. Earlier studies have demonstrated that an increase in the abundance of Proteobacteria and decreased abundance of the phyla Actinobacteria and Bacteroidetes are particularly associated with adverse health outcomes and immunological disorders. Therefore, we propose that pollution-induced shifts in natural soil bacterial community, like in PAH-polluted areas, can contribute to the prevalence of chronic diseases. We encourage studies that simultaneously address the classic "adverse toxin effect" paradigm and our novel "altered environmental microbiome" hypothesis.

Changes in leaching, availability, bioaccumulation, and vertical distribution of lead (Pb) in soil 20 years after the cessation of shooting activity were studied by comparing three pine forest sites in southern Finland: an active shooting range, an abandoned shooting range, and a noncontaminated control site. At both shooting ranges, shooting activity had lasted for 20 years, but it had taken place 20 years earlier at the abandoned range. Up to 4 kg m−2 of Pb pellets had accumulated in the soil at both shooting ranges, and extremely high Pb concentrations, reaching 50,000 mg kg−1, were detected in the organic soil layer. Elevated Pb concentrations were also found in leachate waters and in the biota. Concentrations of Pb in the top organic soil layer and in some of the biota were lower at the abandoned shooting range, which can be taken as a sign of starting recovery of the forest ecosystem. However, the concentration of water-extractable Pb had not decreased in the topsoil, possibly indicating the release of Pb from decaying litter. Deeper in the organic soil layer, weathering of Pb pellets enhanced Pb availability and leaching, indicating an increased risk of groundwater contamination over time at shooting sites located above aquifers. Environ. Toxicol. Chem. 2012; 31: 2771–2779. © 2012 SETAC

Partial removal of the forest humus layer was performed in nitrogen-enriched urban Scots pine forest stands in the northern Finland in order to improve soil conditions for ectomycorrhizal (ECM) fungi, important symbionts of trees. Aboveground part of understory vegetation and the uppermost half of the humus layer were removed (REMOVAL treatment) from sample plots in six urban and eight rural reference forest sites at the beginning of the 2001 growing season. During the seasons 2001-2005, we inventoried sporocarp production of ECM and saprophytic fungi, and in 2003 the recovery of understory vegetation. The REMOVAL treatment resulted in a higher number of fruiting ECM species and sporocarps than controls at the rural, but not at urban sites. The sporocarp number of saprophytic fungi declined in the REMOVAL subplots at the urban sites. The recovery of bryophytes and lichens in the REMOVAL treatment was slow at both the urban and rural sites, whereas Vaccinium dwarf shrub cover, and herb and grass cover returned rapidly at the urban sites. We conclude that the partial vegetation and humus layer removal as a tool to promote the reproduction of ECM fungal species is limited in the boreal urban forests.

Retreating glaciers and the periglacial areas that they vacate produce a harsh environment of extreme radiation, nutrient limitations and temperature oscillations. They provide a model system for studying mechanisms that drive the establishment and early assembly of communities. Here, we synthesize more than 20 yr of research at the Lyman Glacier forefront in the North Cascades Mountains, comparing the results and conclusions for plant and fungal communities. Compared to plant communities, the trajectories and processes of fungal community development are difficult to deduce. However, a combination of high throughput sequencing, more revealing experimental designs, and phylogenetic community analyses provide insights into mechanisms that shape early microbial communities. While the inoculum is likely to be randomly drawn from regional pools and accumulates over time, our data provide no support for increases in richness over time since deglaciation, as is commonly observed for plant communities. Re-analyses of existing datasets suggest that microbial, and particularly fungal, communities are insensitive to time since substrate exposure from underneath the retreating glacier, but are responsive to plant establishment both in biomass and community composition. Further research on functional aspects, organismal activity, or ecosystem services in early successional environments will provide deeper appreciation of the dynamics of these communities.

Nitrogen (N) deposition results in accumulation of N-rich organic matter in urban forests. Partial removal of vegetation and humus layer (REMOVAL treatment) was used to reduce N content of soil and to improve the establishment and performance of planted Scots pine ( Pinus sylvestris L.) seedlings in urban boreal forest sites. Corresponding rural sites of a similar forest type with background N deposition were used as a reference. The REMOVAL treatment increased shoot and root biomass of the seedlings, but did not affect fungal biomass in the roots. The treatment decreased peroxidase activity, an indicator of physiological stress, in roots, which suggests an overall improvement of soil conditions. Present results thus imply amelioration of stress in Scots pine roots in urban soil environment by partial removal of vegetation and the humus layer.

Boreal forests contain diverse fungal communities that form essential ectomycorrhizal symbioses with trees. To determine the effects of lead (Pb) contamination on ectomycorrhizal fungal communities associated with the dominant pine (Pinus sylvestris L.), we surveyed sporocarps for 3 years, analyzed morphotyped ectomycorrhizal root tips by direct sequencing, and 454-sequenced fungal communities that grew into in-growth bags during a 2-year incubation at a shooting range where sectors vary in the Pb load. We recorded a total of 32 ectomycorrhizal fungi that formed conspicuous sporocarps, 27 ectomycorrhizal fungal phylotypes from 294 root tips, and 116 ectomycorrhizal fungal operation taxonomic unit (OTUs) from a total of 8194 internal transcribed spacer-2 454 sequences. Our ordination analyses by nonparametric multidimensional scaling (NMS) indicated that the Pb enrichment induced a shift in the ectomycorrhizal community composition. This was visible as indicative trends in the sporocarp and root tip data sets, but was explicitly clear in the communities observed in the in-growth bags. The compositional shift in the ectomycorrhizal community was mainly attributable to an increase in the frequencies of OTUs assigned to genus Thelephora and to a decrease in the OTUs assigned to Pseudotomentella, Suillus, and Tylospora in Pb-contaminated areas when compared with the control. While the compositional shifts are clear, their functional consequences for the dominant trees or soil ecosystem function remain undetermined.

Most of the empirical evidence available from different types of ecosystems have shown that aboveground plant-based and belowground decomposer systems are interconnected, and change in one leads to a response in the other. We analyzed responses of the soil decomposer system and soil decomposition processes to grazing exclusion and associated vegetation changes in a mountain snowbed. These habitats are of low productivity supporting bryophyte and graminoid-rich vegetation which is grazed by the Norwegian lemming and reindeer. We measured bacteria, enchytraeids, fungi, nematodes, microbial respiration, soil nitrogen (ammonium and nitrate), and soil water content from exclosure treatment plots of 5 and 15 years, where the exclusion of grazers had led to considerable vegetation changes. Soil decomposer variables showed only weak responses to the exclosure treatments or changes in aboveground vegetation (biomass and dead organic matter). Only nematodes responded positively to the short-term grazing exclusion. This suggests that above- and belowground processes are not necessarily closely interconnected in snowbed habitats and that the decomposition of plant material is directly controlled by grazer activity.

Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N2O emission and suppress CH4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO2 emission. The fluxes of CH4, N2O and CO2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH4 oxidation potential, CO2 production, net nitrification and N2O production were studied in laboratory incubations. The mean in situ N2O emissions and in situ CO2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μg N2O m−2 h−1 and from 533 to 611 mg CO2 m−2 h−1. However, ash increased the CH4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH4 uptake rates in situ. The mean in situ CH4 uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μg m−2 h−1, respectively.

Plant biomass, root colonization by ectomycorrhizal (ECM) fungi and root peroxidase (POD) activity were monitored in Scots pine (Pinus sylvestris L.) nursery seedlings during the first growing season after planting (after 4, 8 and 16 weeks, in July, August and October, respectively) in forest humus in outdoor open-top chambers with gaseous atmospheric pollutants (combinations of low levels of ozone, sulfur dioxide and nitrogen oxides). The number of ECM morphotypes as well as root biomass increased towards the end of the growing season, while root POD activity decreased. Fungal biomass estimated as ergosterol concentration peaked in August, 8 weeks after planting. The seedling growth, mycorrhizal status and POD activity in the roots were not affected by the gaseous pollutants.

Fungal and plant community structures were studied in mature Scots pine stands along an urban pollution gradient with four zones of pollution intensity around the city of Oulu, northern Finland. For fungi sporocarp inventories and characterization of ectomycorrhizal (ECM) morphotypes were used and for plants coverage analyses were made. Significant differences were found in community structure of macrofungi and plants along the gradient. The number of ECM species and their sporocarp production, especially those of Cortinarius spp., diminished towards the emission sources, whereas the fruiting of saprotrophic fungi increased close to the emission sources. Eight fruiting macrofungal species reflected the differences between the pollution zones. The species decreasing towards the emission sources were almost all ectomycorrhizal (Chroogomphus rutilus, Cortinarius anomalus, C. brunneus, C. gentilis, C. semisanguineus, Suillus variegatus), with only one species, Cantharellula umbonata considered as saprotrophic. In contrast, ectomycorrhizal Paxillus involutus proved to be pollution-tolerant. The diversity of ECM species was lowest at the most polluted zone while the diversity of plant species increased towards the emission sources. The diversity among ECM morphotypes and saprotrophic species did not differ between the zones. Close to the emission sources slowly growing plant species were displaced by species typical for more nutrient-rich forests, herbs and grasses being more abundant while the number of bryophyte species diminished and lichens were absent. The observed differences in fungal and plant communities are suggested to be results of long-term nitrogen-mediated changes and they support the hypothesis that nitrogen inputs lead to loss of fruiting ECM species. Die Strukturen von Pilz- und Pflanzengemeinschaften wurden in Kiefernwaldern entlang eines stadtischen Gradienten mit vier Zonen unterschiedlicher Verschmutzungsintensitat um die Stadt Oulu im nordlichen Finnland studiert. Zur Erfassung der Pilze wurden Sporokarp-Bestandsaufnahmen gemacht und Ektomykorrhiza (ECM) Morphotypen dargestellt. Gefasspflanzen wurden in Aufnahmen von Deckungsgraden erfasst. Entlang des Gradienten wurden signifikante Unterschiede in der Gemeinschaftsstruktur der Makrofungi und Gefasspflanzen entdeckt. Die Anzahl der ECM-Arten und deren Sporokarpbildung, insbesondere von Cortinarius spp., nahm in Richtung auf die Emissionsquellen hin ab, wohingegen die Produktion von Fruchtkorpern saprophytischer Pilze in der Nahe der Emissionsquellen zunahm. Acht fruchtkorperbildende Makrofungusarten spiegelten die Unterschiede zwischen den Verschmutzungszonen wider. Die Arten, die in Richtung auf die Verschmutzungsquellen hin abnahmen waren Ektomycorrhiza-Arten (Chroogomphus rutilus, Cortinarius anomalus, C. brunneus, C. gentilis, C. semisanguineus, Suillus variegatus), mit Ausnahme von Cantharelulla umbonata, die als saprophytisch eingestuft wird. Im Gegensatz dazu zeigte sich die Ektomykorrhiza-Art Paxillus involutus als verschmutzungstolerant. Die Diversitat der ECM-Arten war am geringsten in der am starksten verschmutzten Zone, wohingegen die Diversitat an Pflanzenarten in Richtung auf die Verschmutzungsquelle hin zunahm. Es gab zwischen den Zonen weder Unterschiede in der Diversitat der ECM Morphotypen noch in der Diversitat der saprophy-tischen Arten. In der Nahe der Verschmutzungsquellen waren langsam wachsende Pflanzenarten ersetzt worden durch Arten, die typisch fur nahrstoffreichere Walder sind; Krauter und Graser waren mehr abundant, wohingegen Moose in Richtung auf die Verschmutzungsquellen hin abnahmen und Flechten in deren Nahe fehlten. Die beobachteten Unterschiede in den Pilz- und Pflanzengemeinschaften sind vermutlich das Ergebnis von langjahrigen stickstoffvermittelten Veranderungen, und sie bestarken die Hypothese, dass Eintrage von Stickstoff zu einem Verlust von fruchtkorperbildenden ECM-Arten fuhrt.

Periglacial substrates exposed by retreating glaciers represent extreme and sensitive environments defined by a variety of abiotic stressors that challenge organismal establishment and survival. The simple communities often residing at these sites enable their analyses in depth. We utilized existing data and mined published sporocarp, morphotyped ectomycorrhizae (ECM), as well as environmental sequence data of internal transcribed spacer (ITS) and large subunit (LSU) regions of the ribosomal RNA gene to identify taxa that occur at a glacier forefront in the North Cascades Mountains in Washington State in the USA. The discrete data types consistently identified several common and widely distributed genera, perhaps best exemplified by Inocybe and Laccaria. Although we expected low diversity and richness, our environmental sequence data included 37 ITS and 26 LSU operational taxonomic units (OTUs) that likely form ECM. While environmental surveys of metabarcode markers detected large numbers of targeted ECM taxa, both the fruiting body and the morphotype datasets included genera that were undetected in either of the metabarcode datasets. These included hypogeous (Hymenogaster) and epigeous (Lactarius) taxa, some of which may produce large sporocarps but may possess small and/or spatially patchy genets. We highlight the importance of combining various data types to provide a comprehensive view of a fungal community, even in an environment assumed to host communities of low species richness and diversity.

Scots pine seedlings were exposed to wet-deposited nickel (Ni) and removal of lichen cover in a dry heath Scots pine forest. Ni deposition affected the colonization of roots by indigenous ectomycorrhizal fungi in contrasting ways in intact and skimmed quadrats. Highest frequencies of tubercle morphotypes of ectomycorrhiza were found in quadrats exposed to 100 mg m−2 year−1 Ni in lichen covered treatment, while in skimmed quadrats these peaked after the treatment with 10 mg Ni m−2 year−1. Removal of the lichen layer increased the value of diversity index (H′) of ectomycorrhizal fungal community, probably due to the increase in the evenness of the morphotype distribution. Lichen removal seemed also to improve the condition of the short roots, as the frequencies of poor and senescent short roots were decreased by the removal.

We investigated the changes in basal respiration (BASAL), microbial biomass as substrate-induced respiration (SIR) and their ratio ( q CO 2 ) in the organic layer along a primary successional transect (alder/rowan, birch, birch/spruce, spruce I and spruce II) typical of the land-uplift coast in western Finland. PLFA analysis was used to detect concurrent successional changes in microbial community structure. Along the transect the soil C/N ratio increased (from 16 to 37) and pH (H 2 O) decreased (from 5.11 to 3.98) substantially. Concurrently, BASAL and SIR remained mainly stable although, during the most favorable temperature and moisture conditions in the field, they tended to increase along the transect from the alder/rowan site to spruce I, and decreased again in spruce II. q CO 2 showed no consistent trend along the transect. The soil of the birch site had the highest total PLFA and bacterial PLFA concentrations, while the soils of both spruce sites had the lowest. The ordination configuration of the PLFA data in non-metric multidimensional scaling was clearly related to the C/N ratio and pH, and separated the forest sites relatively well. It was possible, on the basis of the similarities in the variation pattern along the transect, to divide the PLFAs into six groups.

We monitored net and gross N transformations in the organic layer along a primary successional transect (alder/rowan, birch, birch/spruce, spruce I and spruce II) typical for the land-uplift coast in Western Finland. The relationships between N transformations, vegetation succession and organic matter quality (i.e. concentration of dissolved forms of N, C/N ratio, moisture and acidity) were then evaluated. Net N mineralisation rates in the organic layer were estimated in 5-week incubation experiments in situ using intact soil cores, and in the laboratory on sieved, fresh organic layer samples. Microbial biomass N (fumigation–extraction) and gross N mineralisation (15N-isotope dilution method), were determined once in the laboratory. The C/N ratio increased and pH and net N mineralisation decreased in the organic layer along the succession transect. The alder/rowan site was the only site to show net nitrification. Microbial biomass N tended to increase along the transect from the alder/rowan site to spruce I, and decreased again in spruce II. Concurrently, gross N mineralisation showed a tentative increasing trend along the transect, although the differences between the sites were non-significant. The higher net N mineralisation rates in the alder/rowan site compared to the spruce sites were thus due to lower microbial immobilisation rather than to greater gross N mineralisation. Possible methodological reasons for the lack of response of gross N mineralisation rate to decreasing soil organic matter quality are discussed.

The formation of the organic layer within Scandinavian forest soil started about 10000 yr ago, following the retreat of the continental ice sheet. Since then the land has been slowly rising in northern Europe and uplift still occurs on the coast of the Bothnian Bay at a rate of about 0.6-0.9 m per 100 yr. Four, 300 m long, successional gradients were studied from the shoreline to a Scots pine (Pinus sylvestris) stand with a fully developed humus layer of a few centimetres' thickness. The plantless shoreline was followed by small foredunes and dunes, characterized by Agrostis stolonifera and Leymus arenarius, respectively, and the deflation basin characterized by lichens and sparse Festuca ovina and Deschampsia flexuosa. The study sites situated in Scots pine stands of about 25 and 40 yr age were characterized by sparse dwarf shrubs, lichens and bryophytes. The amount of organic matter in soil increased along the gradient. When the microbial biomass, estimated as indicative phospholipid fatty acids (PLFAs)...

Hydrological conditions are considered to be among the main drivers influencing the export of dissolved organic carbon (DOC) from terrestrial to aquatic ecosystems, and hydrology is likely to alter due to climate change. We built a mesocosm experiment by using peat profiles from a pristine and from a drained (drained in 1978) peatland. A several-week-long low water table period followed by a high water table period, that is, a setting mimicking drought followed by flood, released relatively more DOC from pristine peat than from drained peat. From pristine peat profiles DOC was released into soil water in such quantities that the concentration of DOC remained stable despite dilution caused by added spring water to the mesocosms. In drained peat the DOC concentrations decreased during the high water table period indicating stronger dilution effect in comparison to pristine peat. At the landscape level DOC load from a drained peatland to the recipient water body may, however, increase during flooding because of high water runoff out of the peatland containing high DOC concentrations relative to the forest and agricultural areas. During the high water table period neither peat type nor water table had any clear impact on carbon dioxide (CO2-C) fluxes.

The aim of this case study was to uncover the consequences of lead pellet-derived heavy lead contamination at a cast-off shooting range in southern Finland, covering aspects from soil chemistry and biology up to ecosystem level. The observed changes in the soil properties of the most contaminated areas suggest that the contamination may be disturbing processes of decomposition and nutrient mineralisation. Also two functionally important groups of soil organisms, microbes (as analysed using the PLFA analysis) and enchytraeid worms, were negatively affected by the contamination. Furthermore, there was an indication of reduced pine litter production at the contaminated areas. On the other hand, lead contamination appears not to have affected pine growth or soil-dwelling nematodes and microarthropods, and the general outlook of the whole ecosystem is that of a healthy forest. Thus, the boreal forest ecosystem studied as a whole appears to bear strong resistance to contamination, despite negative effects of lead on many of its components. This resistance may result from e.g. low bioavailability of lead, avoidance of the most contaminated soil horizons and microsites by the organisms, and functional redundancy and development of lead-tolerant populations amongst the organisms. The relative importance of these factors and the mechanisms behind them will be investigated in forthcoming studies.