Rauni Strömmer

SOIL MICROBIAL ACTIVITY AND COMMUNITY STRUCTURE ALONG A PRIMARY SUCCESSION TRANSECT ON THE LAND-UPLIFT COAST IN WESTERN FINLAND

Abstract 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.

Soil microbial activity and biomass in the primary succession of a dry heath forest

Changes in vegetation, soil organic matter content, soil nutrient concentration, microbial activity and microbial biomass were studied in Scots pine (Pinus sylvestris) forests on the post-glacial land uplift island of Hailuoto in Finland, along altitudinal transects representing about 1000 years of primary succession. The characteristics of microbial communities in the humus layer were compared both within altitude classes and within TWINSPAN (two-way indicator species analysis) clusters of field layer vegetation. Non-metric multidimensional scaling (NMDS) was employed to reveal gradients in the data. During succession, the vegetation changed from dominance by bryophytes and deciduous dwarf shrubs to evergreen dwarf shrubs and lichens. The thickness of the humus layer and the amount of organic matter in the soil decreased along the succession, which in turn reduced microbial biomass, microbial activity and soil nutrients when calculated on an areal basis. The nutrient concentration of the soil OM (organic matter) showed no successional trend on a concentration basis but the C-to-N ratio of organic matter increased with increasing soil age and lichen coverage. Thus, the nutrient availability decreased during succession but this could not be demonstrated by calculating results against unit weight of organic matter. Soil basal respiration and microbial biomass increased during the succession when calculated per unit weight of organic matter. The successional decrease in site productivity appeared to be due to leaching of nutrients from the sandy mineral soil and thinning of the humus layer. Plants and soil microbes became increasingly N limited during the course of the succession, suggesting the increased importance of mycorrhizal symbiosis for plant performance and increased energy costs among soil microbes in nutrient uptake.

Soil nitrogen transformations along a primary succession transect on the land-uplift coast in western Finland

Abstract 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.

EcM fungal community structure, but not diversity, altered in a Pb‐contaminated shooting range in a boreal coniferous forest site in Southern Finland

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.

Diversity of macrofungi and plants in Scots pine forests along an urban pollution gradient

Abstract 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.

Urban polluted forest soils induce elevated root peroxidase activity in Scots pine (Pinus sylvestris l.) seedlings

Plant biomass. mycorrhizal status and root peroxidase activity were measured in ectomycorrhizal Scots pine (Pinus sylvestris L.) seedlings grown in urban polluted and native, non-polluted forest soils with added ammonium or potassium sulphates simulating N and S deposition of urban areas. Peroxidase activity in the fine roots of seedlings planted in polluted forest soils was higher than in those planted in non-polluted soils and correlated positively with the activities measured in an earlier study in the roots of mature Scots pines growing at the sites from where the soils were collected. Growth of seedlings and mycorrhizal status were not affected by the origin of soil. Exposing the seedlings to winter acclimation conditions for 6 weeks elevated peroxidase activity in the roots. The addition of ammonium or potassium sulphate to non-polluted soils did not induce elevated root peroxidase activity, although at the levels of 0.5 and 1.0 g of ammonium sulphate a slight increasing trend was observed. We suggest, that indirect biotic factors, i.e. changes in the community structure of soil fungi, early stages of recognition, and defence reactions of pine roots against saprophytic and pathogenic fungi may be participating in the elicitation of peroxidase (POD) activity, although the possible role of heavy metals cannot be excluded.

Soil microbial communities are shaped by vegetation type and park age in cities under cold climate

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 and 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 harboured 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.

The fate of lead at abandoned and active shooting ranges in a boreal pine forest

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.

Does the lichen mat alleviate the effects of wet deposited nickel on soil microorganisms and Scots pine (Pinus sylvestris L.) seedlings

A field experiment was conducted in a dry heath forest dominated by Scots pine (Pinus sylvestris L.) and a mat-forming lichen (Cladina stellaris (Opiz) Brodo) to assess the effect of wet-deposited nickel (Ni) on pine seedlings and soil microorganisms, and to explore whether an intact lichen mat could act as a buffer against heavy metal deposits. Pine seedlings were planted in quadrats covered by a natural lichen layer and in quadrats from which the lichen layer had been completely removed. The quadrats were exposed to four levels of Ni deposition: 0 (i.e., distilled water), 10, 100 and 1000 mg m−2 year−1 in two growing seasons. Increasing Ni deposition led to an increase in the Ni content of the needles, roots and the soil organic layer. The lichen mat reduced Ni flow to the organic soil layer, but had no significant, reducing effect on needle or root Ni concentration. The most severe Ni treatment had detrimental effects on seedling growth and increased peroxidase activity in the previous years needles. Removal of the lichen layer did not increase susceptibility of seedlings to Ni. Values of maximal carbon use efficiency (Max) and metabolic quotient (qCO2) of the soil microorganisms indicated protective value of the lichen mat to soil microorganisms at the highest Ni treatment. Skimming per se decreased basal respiration, qCO2 and concentrations of potassium in the soil and also increased the lag period of the microorganisms as a response to in situ substrate addition.

The abundance of health-associated bacteria is altered in PAH polluted soils - Implications for health in urban areas

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.