Soil and land use research in Europe: Lessons learned from INSPIRATION bottom-up strategic research agenda setting.

We introduce the INSPIRATION bottom-up approach for the development of a strategic research agenda for spatial planning, land use and soil-sediment-water-system management in Europe. Research and innovation needs were identified by more than 500 European funders, endusers, scientists, policy makers, public administrators and consultants. We report both on the concept and on the implementation of the bottom-up approach, provide a critique of the process and draw key lessons for the development of research agendas in the future. Based on identified strengths and weaknesses we identified as key opportunities and threats 1) a high ranking and attentiveness for the research topics on the political agenda, in press and media or in public awareness, 2) availability of funding for research, 3) the resources available for creating the agenda itself, 4) the role of the sponsor of the agenda development, and 5) the continuity of stakeholder engagement as bases for identification of windows of opportunity, creating ownership for the agenda and facilitating its implementation. Our derived key recommendations are 1) a clear definition of the area for which the agenda is to be developed and for the targeted user, 2) a conceptual model to structure the agenda, 3) making clear the expected roles, tasks, input formats regarding the involvement and communication with the stakeholders and project partners, 4) a sufficient number of iterations and checks of the agenda with stakeholders to insure completeness, relevance and creation of co-ownership for the agenda, and 5) from the beginning prepare the infrastructure for the network to implement the agenda.

Toxicity of vanadium in soil on soybean at different growth stages.

Vanadium(V) is present in trace amounts in most plants and widely distributed in soils. However, the environmental toxicity of V compound in soils is controversial. A greenhouse study with soybean from germination to bean production under exposure to pentavalent V [V(V)] was conducted to elucidate the interaction of plants and V fractions in soils and to evaluate the toxicity of V at different plant growth stages. Soybean growth has no effect on non-specific-bond and specific-bond fractions of V in soils, but V fractionation occurred in more extraction-resistant phases at high V concentrations. High concentrations of V(V) postponed the germination and growth of the soybeans. Bean production was less than half of that of the control at 500 mg kg-1 spiked V(V). For the 0 mg kg-1 spiked V(V) treated plants, the root was not the main location where V was retained. Vanadium in the soils at ≤ 250 mg kg-1 did not significantly affect the V concentration in the shoot and leaf of soybeans. With the increase in V concentration in soil, V concentrations in roots increased, whereas those in beans and pods decreased. From vegetative growth to the reproductive growth, the soybeans adsorbed more V and accumulated more V in the roots, with <20% transported to the aboveground parts. Hence, the analysis of V concentration in vegetative tissues or beans may not be a useful indicator for V pollution in soil. Meanwhile, the ratio of V concentration in cell wall to the total V concentration in the root increased with the increase in V(V) concentration in soils. Our results revealed that high concentrations of V inhibited soybean germination and biomass production. However, plants may produce self-defense systems to endure V toxicity.

High Temporal and Spatial Variability of Atmospheric-Methane Oxidation in Alpine Glacier Forefield Soils.

Glacier forefield soils can provide a substantial sink for atmospheric CH4, facilitated by aerobic methane-oxidizing bacteria (MOB). However, MOB activity, abundance, and community structure may be affected by soil age, MOB location in different forefield landforms, and temporal fluctuations in soil physical parameters. We assessed the spatial and temporal variability of atmospheric-CH4 oxidation in an Alpine glacier forefield during the snow-free season of 2013. We quantified CH4 flux in soils of increasing age and in different landforms (sandhill, terrace, and floodplain forms) by using soil gas profile and static flux chamber methods. To determine MOB abundance and community structure, we employed pmoA gene-based quantitative PCR and targeted amplicon sequencing. Uptake of CH4 increased in magnitude and decreased in variability with increasing soil age. Sandhill soils exhibited CH4 uptake rates ranging from -3.7 to -0.03 mg CH4 m-2 day-1 Floodplain and terrace soils exhibited lower uptake rates and even intermittent CH4 emissions. Linear mixed-effects models indicated that soil age and landform were the dominating factors shaping CH4 flux, followed by cumulative rainfall (weighted sum ≤4 days prior to sampling). Of 31 MOB operational taxonomic units retrieved, ∼30% were potentially novel, and ∼50% were affiliated with upland soil clusters gamma and alpha. The MOB community structures in floodplain and terrace soils were nearly identical but differed significantly from the highly variable sandhill soil communities. We concluded that soil age and landform modulate the soil CH4 sink strength in glacier forefields and that recent rainfall affects its short-term variability. This should be taken into account when including this environment in future CH4 inventories.IMPORTANCE Oxidation of methane (CH4) in well-drained, "upland" soils is an important mechanism for the removal of this potent greenhouse gas from the atmosphere. It is largely mediated by aerobic, methane-oxidizing bacteria (MOB). Whereas there is abundant information on atmospheric-CH4 oxidation in mature upland soils, little is known about this important function in young, developing soils, such as those found in glacier forefields, where new sediments are continuously exposed to the atmosphere as a result of glacial retreat. In this field-based study, we investigated the spatial and temporal variability of atmospheric-CH4 oxidation and associated MOB communities in Alpine glacier forefield soils, aiming at better understanding the factors that shape the sink for atmospheric CH4 in this young soil ecosystem. This study contributes to the knowledge on the dynamics of atmospheric-CH4 oxidation in developing upland soils and represents a further step toward the inclusion of Alpine glacier forefield soils in global CH4 inventories.

Isotope fractionation associated with the simultaneous biodegradation of multiple nitrophenol isomers by Pseudomonas putida B2.

Quantifying the extent of biodegradation of nitroaromatic compounds (NACs) in contaminated soils and sediments is challenging because of competing oxidative and reductive reaction pathways. We have previously shown that the stable isotope fractionation of NACs reveals the routes of degradation even if it is simultaneously caused by different bacteria. However, it is unclear whether compound-specific isotope analysis (CSIA) can be applied in situations where multiple pollutants are biodegraded by only one microorganism under multi-substrate conditions. Here we examined the C and N isotope fractionation of 2-nitrophenol (2-NP) and 3-nitrophenol (3-NP) during biodegradation by Pseudomonas putida B2 through monooxygenation and partial reductive pathways, respectively, in the presence of single substrates vs. binary substrate mixtures. Laboratory experiments showed that the reduction of 3-NP by Pseudomonas putida B2 is associated with large N and minor C isotope fractionation with C and N isotope enrichment factors, εC and εN, of -0.3 ± 0.1‰ and -22 ± 0.2‰, respectively. The opposite isotope fractionation trends were found for 2-NP monooxygenation. In the simultaneous presence of 2-NP and 3-NP, 2-NP is biodegraded at identical rate constants and εC and εN values (-1.0 ± 0.1‰ and -1.3 ± 0.2‰) to those found for the monooxygenation of 2-NP in single substrate experiments. While the pathway and N isotope fractionation of 3-NP reduction (εN = -24 ± 1.1‰) are independent of the presence of 2-NP, intermediates of 2-NP monooxygenation interfere with 3-NP reduction. Because neither pH, substrate uptake, nor aromatic substituents affected the kinetic isotope effects of nitrophenol biodegradation, our study illustrates that CSIA provides robust scientific evidence for the assessment of natural attenuation processes.

Structures of Microbial Communities in Alpine Soils: Seasonal and Elevational Effects.

Microbial communities in alpine environments are exposed to several environmental factors related to elevation and local site conditions and to extreme seasonal variations. However, little is known on the combined impact of such factors on microbial community structure. We assessed the effects of seasonal variations on soil fungal and bacterial communities along an elevational gradient (from alpine meadows to a glacier forefield, 1930-2519 m a.s.l.) over 14 months. Samples were taken during all four seasons, even under the winter snowpack and at snowmelt. Microbial community structures and abundances were investigated using Terminal Restriction Fragment Length Polymorphism (T-RFLP) and quantitative PCR (qPCR) of the 16S and 18S rRNA genes. Illumina sequencing was performed to identify key bacterial groups in selected samples. We found that the soil properties varied significantly with the seasons and along the elevational gradient. For example, concentrations of soluble nutrients (e.g., [Formula: see text], [Formula: see text], [Formula: see text]) significantly increased in October but decreased drastically under the winter snowpack. At all times, the alpine meadows showed higher soluble nutrient concentrations than the glacier forefield. Microbial community structures at the different sites were strongly affected by seasonal variations. Under winter snowpack, bacterial communities were dominated by ubiquitous groups (i.e., beta-Proteobacteria, which made up to 25.7% of the total reads in the glacier forefield). In the snow-free seasons, other groups (i.e., Cyanobacteria) became more abundant (from 1% under winter snow in the glacier forefield samples to 8.1% in summer). In summary, elevation had a significant effect on soil properties, whereas season influenced soil properties as well as microbial community structure. Vegetation had a minor impact on microbial communities. At every elevation analyzed, bacterial, and fungal community structures exhibited a pronounced annual cycle.

Methanotrophic and Methanogenic Communities in Swiss Alpine Fens Dominated by Carex rostrata and Eriophorum angustifolium.

Vascular plants play a key role in controlling CH4 emissions from natural wetlands, because they influence CH4 production, oxidation, and transport to the atmosphere. Here we investigated differences in the abundance and composition of methanotrophic and methanogenic communities in three Swiss alpine fens dominated by different vascular plant species under natural conditions. The sampling locations either were situated at geographically distinct sites with different physicochemical properties but the same dominant plant species (Carex rostrata) or were located within the same site, showing comparable physicochemical pore water properties, but had different plant species (C. rostrata or Eriophorum angustifolium). All three locations were permanently submerged and showed high levels of CH4 emissions (80.3 to 184.4 mg CH4 m(-2) day(-1)). Soil samples were collected from three different depths with different pore water CH4 and O2 concentrations and were analyzed for pmoA and mcrA gene and transcript abundance and community composition, as well as soil structure. The dominant plant species appeared to have a significant influence on the composition of the active methanotrophic communities (transcript level), while the methanogenic communities differed significantly only at the gene level. Yet no plant species-specific microbial taxa were discerned. Moreover, for all communities, differences in composition were more pronounced with the site (i.e., with different physicochemical properties) than with the plant species. Moreover, depth significantly influenced the composition of the active methanotrophic communities. Differences in abundance were generally low, and active methanotrophs and methanogens coexisted at all three locations and depths independently of CH4 and O2 concentrations or plant species.

Microbial abundance and community structure in a melting alpine snowpack.

Snowmelt is a crucial period for alpine soil ecosystems, as it is related to inputs of nutrients, particulate matter and microorganisms to the underlying soil. Although snow-inhabiting microbial communities represent an important inoculum for soils, they have thus far received little attention. The distribution and structure of these microorganisms in the snowpack may be linked to the physical properties of the snowpack at snowmelt. Snow samples were taken from snow profiles at four sites (1930-2519 m a.s.l.) in the catchment of the Tiefengletscher, Canton Uri, Switzerland. Microbial (Archaea, Bacteria and Fungi) communities were investigated through T-RFLP profiling of the 16S and 18S rRNA genes, respectively. In parallel, we assessed physical and chemical parameters relevant to the understanding of melting processes. Along the snow profiles, density increased with depth due to compaction, while other physico-chemical parameters, such as temperature and concentrations of DOC and soluble ions, remained in the same range (e.g. <2 mg DOC L(-1), 5-30 µg NH4 (+)-N L(-1)) in all samples at all sites. Along the snow profiles, no major change was observed either in cell abundance or in bacterial and fungal diversity. No Archaea could be detected in the snow. Microbial communities, however, differed significantly between sites. Our results show that meltwater rearranges soluble ions and microbial communities in the snowpack.

Methane dynamics in an alpine fen: a field-based study on methanogenic and methanotrophic microbial communities.

Wetlands are important sources of the greenhouse gas methane (CH4). We provide an in situ study of CH4 dynamics in the permanently submerged soil of a Swiss alpine fen. Physico-chemical pore water analyses were combined with structural and microbiological analyses of soil cores at high vertical resolution down to 50 cm depth. Methanotrophs and methanogens were active throughout the depth profile, and highest abundance of active methanotrophs and methanogens [6.1 × 10(5) and 1.1 × 10(7) pmoA and mcrA transcripts (g soil)(-1), respectively] was detected in the uppermost 2 cm of the soil. Active methanotrophic communities in the near-surface zone, dominated by viable mosses, varied from the communities in the deeper zones, but further changes with depth were not pronounced. Apart from a distinct active methanogenic community in the uppermost sample, a decrease of acetoclastic Methanosaetaceae with depth was observed in concomitance with decreasing root surface area. Overall, root surface area correlated with mcrA transcript abundance and CH4 pore water concentrations, which peaked (137.1 µM) at 10 to 15 cm depth. Our results suggest that stimulation of methanogenesis by root exudates of vascular plants had a stronger influence on CH4 dynamics than stimulation of CH4 oxidation by O2 input.

Vertical distribution of the soil microbiota along a successional gradient in a glacier forefield.

Spatial patterns of microbial communities have been extensively surveyed in well-developed soils, but few studies investigated the vertical distribution of micro-organisms in newly developed soils after glacier retreat. We used 454-pyrosequencing to assess whether bacterial and fungal community structures differed between stages of soil development (SSD) characterized by an increasing vegetation cover from barren (vegetation cover: 0%/age: 10 years), sparsely vegetated (13%/60 years), transient (60%/80 years) to vegetated (95%/110 years) and depths (surface, 5 and 20 cm) along the Damma glacier forefield (Switzerland). The SSD significantly influenced the bacterial and fungal communities. Based on indicator species analyses, metabolically versatile bacteria (e.g. Geobacter) and psychrophilic yeasts (e.g. Mrakia) characterized the barren soils. Vegetated soils with higher C, N and root biomass consisted of bacteria able to degrade complex organic compounds (e.g. Candidatus Solibacter), lignocellulolytic Ascomycota (e.g. Geoglossum) and ectomycorrhizal Basidiomycota (e.g. Laccaria). Soil depth only influenced bacterial and fungal communities in barren and sparsely vegetated soils. These changes were partly due to more silt and higher soil moisture in the surface. In both soil ages, the surface was characterized by OTUs affiliated to Phormidium and Sphingobacteriales. In lower depths, however, bacterial and fungal communities differed between SSD. Lower depths of sparsely vegetated soils consisted of OTUs affiliated to Acidobacteria and Geoglossum, whereas depths of barren soils were characterized by OTUs related to Gemmatimonadetes. Overall, plant establishment drives the soil microbiota along the successional gradient but does not influence the vertical distribution of microbiota in recently deglaciated soils.

Bacterial Composition and Survival on Sahara Dust Particles Transported to the European Alps.

Deposition of Sahara dust (SD) particles is a frequent phenomenon in Europe, but little is known about the viability and composition of the bacterial community transported with SD. The goal of this study was to characterize SD-associated bacteria transported to the European Alps, deposited and entrapped in snow. During two distinct events in February and May 2014, SD particles were deposited and promptly covered by falling snow, thus preserving them in distinct ochre layers within the snowpack. In June 2014, we collected samples at different depths from a snow profile at the Jungfraujoch (Swiss Alps; 3621 m a.s.l.). After filtration, we performed various microbiological and physicochemical analyses of the snow and dust particles therein that originated in Algeria. Our results show that bacteria survive and are metabolically active after the transport to the European Alps. Using high throughput sequencing, we observed distinct differences in bacterial community composition and structure in SD-layers as compared to clean snow layers. Sporulating bacteria were not enriched in the SD-layers; however, phyla with low abundance such as Gemmatimonadetes and Deinococcus-Thermus appeared to be specific bio-indicators for SD. Since many members of these phyla are known to be adapted to arid oligotrophic environments and UV radiation, they are well suited to survive the harsh conditions of long-range airborne transport.

Physical extraction of microorganisms from water-saturated, packed sediment.

Microbial characterization of aquifers should include samples of both suspended and attached microorganisms (biofilms). We investigated the effect of shear, sonication, and heat on the extraction of microorganisms from water-saturated, packed sediment columns containing established biofilms. Shear was studied by increasing flow velocity of the column eluent, sonication by treating the columns with ultrasound at different power levels, and heat by warming up the column eluent to different temperatures. Effluent cell concentrations were used as a measure of extraction efficiency. Dissolved organic carbon and adenosine tri-phosphate (ATP) concentrations were used to corroborate cell-extraction results. Additionally, ATP was used as an indicator of cell-membrane integrity. Extraction quality was determined by comparing terminal-restriction fragment length polymorphism (T-RFLP) profiles of extracted bacterial communities with destructively sampled sediment-community profiles. Sonication and heat increased the extraction efficiency up to 200-fold and yielded communities comparable to the sediment community. These treatments showed high potential for in-situ application in aquifers.

Diversity, resistance and resilience of the bacterial communities at two alpine glacier forefields after a reciprocal soil transplantation.

In this study, we determined the driving key factor determining variability in bacterial community structures in soils at two unvegetated alpine glacier forefields with different bedrock geology (calcareous and siliceous). We further assessed the resistance and resilience capacities of the bacterial communities through reciprocal soil transplantations. Sterilized and unsterilized soils were incubated locally ('home') or transplanted ('away') for 15 months (July 2011-October 2012) and sampled regularly during the snow-free seasons. Changes in bacterial community structures were determined through fingerprinting of the 16S rRNA gene and correlated with several environmental factors. This study demonstrates that bacterial community structures at our field sites were shaped by distinct mineralogical soil properties. Soil moisture and pH appeared to not be the major driving key factors. Calcareous soil was more selective to bacteria, thus diversity was higher in siliceous soils as a positive effect of its more diverse mineralogical composition. Bacterial community in the calcareous soil exhibited stronger resistance to transplantation than the community in the siliceous soil. In fact, siliceous soil was more easily invaded by extrinsic taxa. Bacterial communities of both soil types were equally resilient at home, although different resilience patterns were observed between calcareous and siliceous soils incubated away.

In-situ sonication for enhanced recovery of aquifer microbial communities.

Sampling methods for characterization of microbial communities in aquifers should target both suspended and attached microorganisms (biofilms). We investigated the effectiveness and reproducibility of low-frequency (200 Hz) sonication pulses on improving extraction efficiency and quality of microorganisms from a petroleum-contaminated aquifer in Studen (Switzerland). Sonication pulses at different power levels (0.65, 0.9, and 1.1 kW) were applied to three different groundwater monitoring wells. Groundwater samples extracted after each pulse were compared with background groundwater samples for cell and adenosine tri-phosphate concentration. Turbidity values were obtained to assess the release of sediment fines and associated microorganisms. The bacterial community in extracted groundwater samples was analyzed by terminal-restriction-fragment-length polymorphism and compared with communities obtained from background groundwater samples and from sediment cores. Sonication enhanced the extraction efficiency up to 13-fold, with most of the biomass being associated with the sediment fines extracted with groundwater. Consecutive pulses at constant power were decreasingly effective, while pulses with higher power yielded the best results both in terms of extraction efficiency and quality. Our results indicate that low-frequency sonication may be a viable and cost-effective tool to improve the extraction of microorganisms from aquifers, taking advantage of existing groundwater monitoring wells.

Isotope fractionation associated with the biodegradation of 2- and 4-nitrophenols via monooxygenation pathways.

Monooxygenation is an important route of nitroaromatic compound (NAC) biodegradation and it is widely found for cometabolic transformations of NACs and other aromatic pollutants. We investigated the C and N isotope fractionation of nitrophenol monooxygenation to complement the characterization of NAC (bio)degradation pathways by compound-specific isotope analysis (CSIA). Because of the large diversity of enzymes catalyzing monooxygenations, we studied the combined C and N isotope fractionation and the corresponding (13)C- and (15)N-apparent kinetic isotope effects (AKIEs) of four nitrophenol-biodegrading microorganisms (Bacillus spharericus JS905, Pseudomonas sp. 1A, Arthrobacter sp. JS443, Pseudomonas putida B2) in the pH range 6.1-8.6 with resting cells and crude cell extracts. While the extent of C and N isotope fractionation and the AKIE-values varied considerably for the different organisms, the correlated C and N isotope signatures (δ(15)N vs δ(13)C) revealed trends, indicative of two distinct monooxygenation pathways involving hydroxy-1,4-benzoquinone or 1,2- and 1,4-benzoquinone intermediates, respectively. The distinction was possible based on larger secondary (15)N-AKIEs associated with the benzoquinone pathway. Isotope fractionation was neither masked substantially by nitrophenol speciation nor transport across cell membranes. Only when 4-nitrophenol was biodegraded by Pseudomonas sp. 1A did isotope fractionation become negligible, presumably due to rate-limiting substrate binding steps pertinent to the catalytic cycle of flavin-dependent monooxygenases.

Chemical extraction of microorganisms from water-saturated, packed sediment.

Microbial characterization of aquifers should combine collection of suspended and attached microorganisms (biofilms). This study investigated chemical extraction of microorganisms from water-saturated, packed sediment containing established biofilms. It compares the use of different detachment-promoting agent (DPA) solutions with tap water as eluent in column experiments. Extraction efficiency was determined from cell concentrations in the column effluent. Adenosine triphosphate concentrations were measured to confirm cell extraction and as an indicator of cell membrane integrity. Quality of extracted bacterial communities was assessed by comparing their terminal restriction fragment length polymorphism profiles with destructively sampled sediment-community profiles. Extraction efficiency increased more than 8-fold when deionized water, D-amino acids, or enzymes were used as a DPA. Community profiles recovered by individual DPA solutions showed more pronounced differences at the level of rare microbial groups, whereas abundant groups appeared ubiquitous across treatments. These results suggest that comparison of communities extracted by different DPAs can provide improved information on the occurrence of rare microbial groups in biofilms.

Succession of N cycling processes in biological soil crusts on a Central European inland dune.

Biological soil crusts (BSCs) are microbial assemblages that occur worldwide and facilitate ecosystem development by nitrogen (N) and carbon accumulation. N turnover within BSC ecosystems has been intensively studied in the past; however, shifts in the N cycle during BSC development have not been previously investigated. Our aim was to characterise N cycle development first by the abundance of the corresponding functional genes (in brackets) and second by potential enzyme activities; we focussed on the four processes: N fixation (nifH), mineralisation as proteolysis and chitinolysis (chiA), nitrification (amoA) and denitrification (nosZ). We sampled from four phases of BSC development and from a reference located in the rooting zone of Corynephorus canescens, on an inland dune in Germany. BSC development was associated with increasing amounts of chlorophyll, organic carbon and N. Potential activities increased and were highest in developed BSCs. Similarly, the abundance of functional genes increased. We propose and discuss three stages of N process succession. First, the heterotrophic stage (mobile sand without BSCs) is dominated by mineralisation activity. Second, during the transition stage (initial BSCs), N accumulates, and potential nitrification and denitrification activity increases. Third, the developed stage (established BSCs and reference) is characterised by the dominance of nitrification.

Freeze-coring method for characterization of microbial community structure and function in wetland soils at high spatial resolution.

A simple freeze-coring method was developed to obtain structurally intact cores from wetland soils. A copper tube was inserted into the wetland and filled with ethanol and dry ice to freeze the surrounding soil. Biological structure and function could be analyzed, and labile compounds such as mRNA were recovered.

Simple absolute quantification method correcting for quantitative PCR efficiency variations for microbial community samples.

Real-time quantitative PCR (qPCR) is a widely used technique in microbial community analysis, allowing the quantification of the number of target genes in a community sample. Currently, the standard-curve (SC) method of absolute quantification is widely employed for these kinds of analysis. However, the SC method assumes that the amplification efficiency (E) is the same for both the standard and the sample target template. We analyzed 19 bacterial strains and nine environmental samples in qPCR assays, targeting the nifH and 16S rRNA genes. The E values of the qPCRs differed significantly, depending on the template. This has major implications for the quantification. If the sample and standard differ in their E values, quantification errors of up to orders of magnitude are possible. To address this problem, we propose and test the one-point calibration (OPC) method for absolute quantification. The OPC method corrects for differences in E and was derived from the ΔΔC(T) method with correction for E, which is commonly used for relative quantification in gene expression studies. The SC and OPC methods were compared by quantifying artificial template mixtures from Geobacter sulfurreducens (DSM 12127) and Nostoc commune (Culture Collection of Algae and Protozoa [CCAP] 1453/33), which differ in their E values. While the SC method deviated from the expected nifH gene copy number by 3- to 5-fold, the OPC method quantified the template mixtures with high accuracy. Moreover, analyzing environmental samples, we show that even small differences in E between the standard and the sample can cause significant differences between the copy numbers calculated by the SC and the OPC methods.

Bacterial, archaeal and fungal succession in the forefield of a receding glacier.

Glacier forefield chronosequences, initially composed of barren substrate after glacier retreat, are ideal locations to study primary microbial colonization and succession in a natural environment. We characterized the structure and composition of bacterial, archaeal and fungal communities in exposed rock substrates along the Damma glacier forefield in central Switzerland. Soil samples were taken along the forefield from sites ranging from fine granite sand devoid of vegetation near the glacier terminus to well-developed soils covered with vegetation. The microbial communities were studied with genetic profiling (T-RFLP) and sequencing of clone libraries. According to the T-RFLP profiles, bacteria showed a high Shannon diversity index (H) (ranging from 2.3 to 3.4) with no trend along the forefield. The major bacterial lineages were Proteobacteria, Actinobacteria, Acidobacteria, Firmicutes and Cyanobacteria. An interesting finding was that Euryarchaeota were predominantly colonizing young soils and Crenarchaeota mainly mature soils. Fungi shifted from an Ascomycota-dominated community in young soils to a more Basidiomycota-dominated community in old soils. Redundancy analysis indicated that base saturation, pH, soil C and N contents and plant coverage, all related to soil age, correlated with the microbial succession along the forefield.

Bacterial chitin hydrolysis in two lakes with contrasting trophic statuses.

Chitin, which is a biopolymer of the amino sugar glucosamine (GlcN), is highly abundant in aquatic ecosystems, and its degradation is assigned a key role in the recycling of carbon and nitrogen. In order to study the significance of chitin decomposition in two temperate freshwater lakes with contrasting trophic and redox conditions, we measured the turnover rate of the chitin analog methylumbelliferyl-N,N'-diacetylchitobioside (MUF-DC) and the presence of chitinase (chiA) genes in zooplankton, water, and sediment samples. In contrast to the eutrophic and partially anoxic lake, chiA gene fragments were detectable throughout the oligotrophic water column and chiA copy numbers per ml of water were up to 15 times higher than in the eutrophic waters. For both lakes, the highest chiA abundance was found in the euphotic zone--the main habitat of zooplankton, but also the site of production of easily degradable algal chitin. The bulk of chitinase activity was measured in zooplankton samples and the sediments, where recalcitrant chitin is deposited. Both, chiA abundance and chitinase activity correlated well with organic carbon, nitrogen, and concentrations of particulate GlcN. Our findings show that chitin, although its overall contribution to the total organic carbon is small (~0.01 to 0.1%), constitutes an important microbial growth substrate in these temperate freshwater lakes, particularly where other easily degradable carbon sources are scarce.