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We investigated the interaction between fungal communities of soil and dead wood substrates. For this, we applied molecular species identification and stable isotope tracking to both soil and decaying wood in an unmanaged boreal Norway spruce-dominated stand. Altogether, we recorded 1990 operational taxonomic units, out of which more than 600 were shared by both substrates and 589 were found to exclusively inhabit wood. On average the soil was more species-rich than the decaying wood, but the species richness in dead wood increased monotonically along the decay gradient, reaching the same species richness and community composition as soil in the late stages. Decaying logs at all decay stages locally influenced the fungal communities from soil, some fungal species occurring in soil only under decaying wood. Stable isotope analyses suggest that mycorrhizal species colonising dead wood in the late decay stages actively transfer nitrogen and carbon between soil and host plants. Most importantly, Piloderma sphaerosporum and Tylospora sp. mycorrhizal species were highly abundant in decayed wood. Soil- and wood-inhabiting fungal communities interact at all decay phases of wood that has important implications in fungal community dynamics and thus nutrient transportation.

Summary Microbial respiration in dead wood contributes substantially to the long‐lived forest carbon (C) pool and has a significant role in the forest nitrogen (N) cycle. Wood N content has been found to increase during the decay process; however, temporal dynamics and the sources of this external N remain unclear. To examine N dynamics at various stages of decomposition, we combined high variety of analytical methods on Norway spruce logs, including wood δ15N, N%, 14C‐dating, fungal composition and N2 fixation rate. For N2 fixation rate, we also determined its dependency on ambient temperature and decay class, when estimating annual N2 fixation rates for our study site. N2 fixation was observed to have a major role in increasing wood N content during decay. For the most decayed wood, it accounted for 60% of the total N accumulation. Compared to other reports, where the annual temperature was similar to our site, the calculated annual fixation rate of 85 g N ha−1 year−1 is a low estimate. However, previous studies have not taken appropriately into account the dependency of N2 fixation rate on ambient temperature and decay class. Our δ15N model describing the sources of external N, statistical analysis and the fungal DNA composition of decayed wood suggest that other sources of external N accumulating in wood were soil‐foraging wood‐decay fungi and mycorrhizal fungi. Our study improves knowledge of the temporal dynamics of N accumulation in wood with advancing wood decay, the potential sources of external N and their relative significance. All of these factors are important for nitrogen as well as carbon models dealing with ecosystem responses to climate change. Lay Summary

Background and aims: Estimation of root-mediated carbon fluxes in forested peatlands is needed for understanding ecosystem functioning and supporting greenhouse gas inventories. Here, we aim to determine the optimal methodology for utilizing ingrowth cores in estimating annual fine-root production (FRP) and its vertical distribution in trees, shrubs and herbs. Methods: We used 3-year data obtained with modified ingrowth core method and tested two calculation methods: 'ingrowth-dividing' and 'ingrowthsubtracting'. Results: The ingrowth-dividing method combined with a 2-year incubation of ingrowth cores can be used for the 'best estimate' of FRP. The FRP in the nutrient-rich fen forest (561 g m⁻²) was more than twice that in the nutrient-poor bog forest (244 g m⁻²). Most FRP occurred in the top 20-cm layer (76-82 %). Tree FRP accounted for 71 % of total FRP in the bog and 94 % in the fen forests, respectively, following the aboveground vegetation patterns; however, in fen forest the proportions of spruce and birch in FRP were higher than their proportions in stand basal area. Conclusions: Our methodology may be used to study peatland FRP patterns more widely and will reduce the volume of labour-intensive work, but will benefit from verification with other methods, as is the case in all in situ FRP studies.

Source point treatment of effluents with a high load of pharmaceutical active compounds (PhACs), such as hospital wastewater, is a matter of discussion among the scientific community. Fungal treatments have been reported to be successful in degrading this type of pollutants and, therefore, the white-rot fungus Trametes versicolor was applied for the removal of PhACs from veterinary hospital wastewater. Sixty-six percent removal was achieved in a non-sterile batch bioreactor inoculated with T. versicolor pellets. On the other hand, the study of microbial communities by means of DGGE and phylogenetic analyses led us to identify some microbial interactions and helped us moving to a continuous process. PhAC removal efficiency achieved in the fungal treatment operated in non-sterile continuous mode was 44 % after adjusting the C/N ratio with respect to the previously calculated one for sterile treatments. Fungal and bacterial communities in the continuous bioreactors were monitored as well.

We measured methane (CH4) exchange rates with automatic chambers at the forest floor of a nutrient-rich drained peatland in 2011–2013. The fen, located in southern Finland, was drained for forestry in 1969 and the tree stand is now a mixture of Scots pine, Norway spruce, and pubescent birch. Our measurement system consisted of six transparent chambers and stainless steel frames, positioned on a number of different field and moss layer compositions. Gas concentrations were measured with an online cavity ring-down spectroscopy gas analyzer. Fluxes were calculated with both linear and exponential regression. The use of linear regression resulted in systematically smaller CH4 fluxes by 10–45 % as compared to exponential regression. However, the use of exponential regression with small fluxes ( <  2.5 µg CH4 m−2 h−1) typically resulted in anomalously large absolute fluxes and high hour-to-hour deviations. Therefore, we recommend that fluxes are initially calculated with linear regression to determine the threshold for low fluxes and that higher fluxes are then recalculated using exponential regression. The exponential flux was clearly affected by the length of the fitting period when this period was  <  190 s, but stabilized with longer periods. Thus, we also recommend the use of a fitting period of several minutes to stabilize the results and decrease the flux detection limit. There were clear seasonal dynamics in the CH4 flux: the forest floor acted as a CH4 sink particularly from early summer until the end of the year, while in late winter the flux was very small and fluctuated around zero. However, the magnitude of fluxes was relatively small throughout the year, ranging mainly from −130 to +100 µg CH4 m−2 h−1. CH4 emission peaks were observed occasionally, mostly in summer during heavy rainfall events. Diurnal variation, showing a lower CH4 uptake rate during the daytime, was observed in all of the chambers, mainly in the summer and late spring, particularly in dry conditions. It was attributed more to changes in wind speed than air or soil temperature, which suggest that physical rather than biological phenomena are responsible for the observed variation. The annual net CH4 exchange varied from −104 ± 30 to −505 ± 39 mg CH4 m−2 yr−1 among the six chambers, with an average of −219 mg CH4 m−2 yr−1 over the 2-year measurement period.

Stable oxygen isotope ratios (δ¹⁸O) in trees from high latitude ecosystems are valuable sources of information for recent and past environmental changes, but the interpretation is hampered by the complex hydrology of forests growing under permafrost conditions, where only a shallow layer of soil thaws in summer. We investigated larch trees (Larix gmelinii) at two sites with contrasting soil conditions in Siberia and determined δ¹⁸O of water from different soil depths, roots, twigs, and needles as well as δ¹⁸O of soluble carbohydrates regularly over two growing seasons. A comparison of results from the 2 yrs revealed an unexpected ‘inverse’ climate‐isotope relationship, as dry and warm summer conditions resulted in lower soil and root δ¹⁸O values. This was due to a stronger uptake of isotopically depleted water pools originating from melted permafrost or previous winter snow. We developed a conceptual framework that considers the dependence of soil water profiles on climatic conditions for explaining δ¹⁸O in needle water, needle soluble carbohydrates and stem cellulose. The negative feedback of drought conditions on the source isotope value could explain decreasing tree‐ring δ¹⁸O trends in a warming climate and is likely relevant in many ecosystems, where a soil isotope gradient with depth is observed.

BACKGROUND AND AIM: Although ombrotrophic peatlands are nutrient deficient, it is not clear to what extent plants will respond to changes in nutrient availability. METHODS: We examined the changes in foliar stoichiometry and species abundance of four shrub species and moss after a decade of nitrogen (N), phosphorus (P) and potassium (K) fertilization at the Mer Bleue bog, eastern Canada. RESULTS: Shrub abundance increased and moss cover decreased after fertilization with 6.4, 5 and 6.3 g m⁻² yr⁻¹ of N, P and K, respectively; foliar concentrations of N, P, K and calcium (Ca) and magnesium (Mg) were affected. Stoichiometry showed mainly N limitation after P and K fertilization and P (co)limitation after high levels of N addition in shrubs; moss showed consistent K or KN-co-limitation, even with PK and NPK additions. Shrubs exhibited the strongest homeostasis (the maintenance of an organism’s tissue chemical composition with changes in environmental resources) to N, with the homeostatic regulation coefficient (H) > 9.7, compared to 1.4 in moss. For P and K, shrubs showed weaker homeostasis than N, while moss had a stronger homeostasis. CONCLUSIONS: The strong homeostasis of shrubs may be an adaptive strategy to limited availability of soil N and P.

Forest harvesting, especially when intensified harvesting method as whole-tree harvesting with stump lifting (WTHs) are used, may increase mercury (Hg) and methylmercury (MeHg) leaching to recipient water courses. The effect can be enhanced if the underlying bedrock and overburden soil contain Hg. The impact of stem-only harvesting (SOH) and WTHs on the concentrations of Hg and MeHg as well as several other variables in the ditch water was studied using a paired catchment approach in eight drained peatland-dominated catchments in Finland (2008–2012). Four of the catchments were on felsic bedrock and four on black schist bedrock containing heavy metals. Although both Hg and MeHg concentrations increased after harvesting in all treated sites according to the randomized intervention analyses (RIAs), there was only a weak indication of a harvest-induced mobilization of Hg and MeHg into the ditches. Furthermore, no clear differences between WTHs and SOH were found, although MeHg showed a nearly significant difference (p = 0.06) between the harvesting regimes. However, there was a clear bedrock effect, since the MeHg concentrations in the ditch water were higher at catchments on black schist than at those on felsic bedrock. The pH, suspended solid matter (SSM), dissolved organic carbon (DOC), and iron (Fe) concentrations increased after harvest while the sulfate (SO₄-S) concentration decreased. The highest abundances of sulfate-reducing bacteria (SRB) were found on the sites with high MeHg concentrations. The biggest changes in ditch water concentrations occurred first 2 years after harvesting.

Tropical peat carbon compound composition (CCC) is a highly understudied subject. Advanced understanding of peat CCC and carbon dynamics in differing conditions is desperately needed due to large-scale utilization of these peatlands. We studied the CCC—i.e. the hemicellulosic carbohydrate and uronic acid composition and concentrations of extractives, cellulose, acid-soluble lignin and acid-insoluble lignin—in association with peat profile depth and physical structure of peat, under representative, common land uses. Samples were gathered from an undrained forest and three sites altered 20–30 years prior to the study, which in aggregate form a continuum of increasing land-use intensity (drainage-affected forest; drained and deforested degraded open site; drained and deforested site under cultivation) in Central Kalimantan, Indonesia. Peat samples were taken from depths between 10 and 115 cm that covered mostly oxic, frequently waterlogged and permanently waterlogged, anoxic conditions. Our results demonstrated greater modification of peat properties when both vegetation and hydrological conditions were altered. The differences between sites were mainly present in the topmost peat and decreased with depth. Peat located at the surface contained more labile compounds (hemicelluloses, extractives, uronic acids, cellulose) on forest sites than at the most intensively altered open sites, where peat was enriched with recalcitrant acid insoluble lignin. The effect of drainage was evident in the drained forest site, where at the approximate median water table depth peat more closely resembled open sites in terms of the peat properties. The increased recalcitrance of peat in reclaimed areas has been a result of enhanced decomposition, reduced litter input rates and, at open sites also by repeated fires.

The use of transplanted moss ( Pleurozium schreberi ) in active biomonitoring of traffic-related emissions of Pd, Pt, and Rh was studied. Moss mats were transplanted to three locations along highway E75 (in Oulu, Finland) at three different distances from the highway. Five samples were collected from a background site after the same exposure period. Mass fractions of Pd, Pt, and Rh as well as mass fractions of 18 other elements were determined in these samples. The results indicated that P. schreberi is well suited for active biomonitoring of Pd, Pt, and Rh. Mass fractions above the background values were observed in the samples exposed to traffic-related emissions. When the results were compared with those of the other elements, high correlations of Pd, Pt, and Rh with commonly traffic-related elements (e.g., Cu, Ni, Sb, Zn, etc.) were found. It was also found that the amounts of Pd, Pt, and Rh in moss samples decreased when the distance to the highway increased. This trend gives evidence for the suitability of P. schreberi for active biomonitoring of Pd, Pt, and Rh. Furthermore, it can be concluded that the mass fractions determined in this study provide valuable evidence about the current state of Pd, Pt, and Rh emissions in Oulu, Finland.