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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.

Fungal communities are important for carbon (C) transformations in boreal forests that are one of the largest C pools in terrestrial ecosystems, warranting thus further investigation of fungal community dynamics in time and space. We investigated fungal diversity and community composition seasonally and across defined soil horizons in boreal Scots pine forest in Finland using 454 pyrosequencing. We collected a total of 120 samples from five vertical soil horizons monthly from March to October; in March, under snow. Boreal forest soil generally harbored diverse fungal communities across soil horizons. The communities shifted drastically and rapidly over time. In late winter, saprotrophs dominated the community and were replaced by ectomycorrhizal fungi during the growing season. Our studies are among the first to dissect the spatial and temporal dynamics in boreal forest ecosystems and highlights the ecological importance of vertically distinct communities and their rapid seasonal dynamics. As climate change is predicted to result in warmer and longer snow-free winter seasons, as well as increase the rooting depth of trees in boreal forest, the seasonal and vertical distribution of fungal communities may change. These changes are likely to affect the organic matter decomposition by the soil-inhabiting fungi and thus alter organic C pools. Fungal communities were diverse also in deeper soil horizons, and they varied significantly both vertically and seasonally; community structure in winter was the most different compared to the growing season.

Abstract Fungal viruses (mycoviruses) are considered to be highly host specific, but phylogenetic analysis supports the occasional occurrence of horizontal transmission between species. We used an extensive sampling strategy to investigate whether similar viruses occur in more than one fungal species of the same forest habitat. Mycelial samples were collected from in-growth mesh bags (N = 259), fruiting bodies (N = 173) and cultured isolates (N = 68) at a forest site where the spatial distribution of viral infections in clonal individuals of the wood decay fungus Heterobasidion parviporum was mapped in detail earlier. The investigation revealed previously known Heterobasidion viruses in ∼2% of the single or pooled mycorrhizal samples from mesh bags, ∼3% of the fruiting body samples and none of the fungal cultures analyzed. Novel virus strains distinct from known Heterobasidion viruses were detected in cultures of ectomycorrhizal fungi (Lactarius tabidus, L. rufus) and saprotrophic fungi (Megacollybia platyphylla, Mucoraceae spp.). Overall, our results support the view that mycoviruses do not readily cross species borders. Regarding potential virocontrol applications, the introduction of Heterobasidion viruses into natural habitats is not expected to cause a major infection pressure towards the indigenous fungal community. However, the ecological consequences of the putative interspecies virus transmission events detected require further investigation. An extensive sampling strategy was used to investigate whether viruses infecting Heterobasidion root rot fungi cause a major infection pressure towards the indigenous fungal community of the boreal forest habitat.

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.

Natural sporulation of Cronartium ribicola and C. flaccidum were investigated on known and potential alternate hosts growing in three botanical gardens representing different geographic regions in Finland and in some natural habitats next to the northern botanical garden. Uredinia and telia of Cronartium were searched for from over 27,000 leaves collected or checked in the field in 66–96 species representing 16 plant families susceptible to Cronartium. Cronartium ribicola was found on 19 species or cultivars, while C. flaccidum occurred on 17 species. Uredinia and telia of Cronartium ribicola lacked in the southern botanical garden, but they occurred on 5–16 Ribes species or cultivars in the other two botanical gardens. Cronartium ribicola sporulated on one to four Ribes rubrum cultivars, one to three R. uva-crispa cultivars, three to seven R. nigrum cultivars, R. aureum and R. glandulosum in the gardens. Cronartium flaccidum sporulated on five to nine species in the botanical gardens including species of Paeonia, Melampyrum, Loasa, Pedicularis and Vincetoxicum. In natural habitats next to the northern botanical garden, C. flaccidum sporulated also on Melampyrum sylvaticum and Euphrasia stricta var. stricta. Among all the infected species, C. flaccidum sporulated most frequently on Paeonia. For the first time, C. flaccidum was found on E. stricta growing in its natural habitat. Although the frequency of infected leaves under natural inoculum was low for several infected species, the large variety of susceptible species serve as an efficient tool for Cronartium to spread. Based on the amount of natural sporulation in the gardens and their surroundings, both Cronartium rusts are widely distributed and sporulate in different geographic areas in Finland.

Despite several studies demonstrating that deep planting has no negative effects on seedling development, conifer seedlings are still typically planted to depths of 3–5 cm in boreal forests. Planting machines plant seedlings deeper. While machine planting has become more common in boreal forests, there is still a need to demonstrate that conifer seedlings can be planted using this method without reduced field performance of seedlings. To investigate the effects of deep planting on Norway spruce ( Picea abies (L.) Karst.) container seedlings, we established two experiments in Central Finland in 2006 and 2009. In the experiment on a site with medium coarse soil, planting depths were 0, 2, 5 and 8 cm. In the experiment established on fine-textured soil, planting depths were 3, 6 and 10 cm. During the first 4 years after planting, deeper planted seedlings grew better and at the end of the fourth season initial differences in shoot length among planting depths had disappeared. Incidence of insect damage was relatively low, and no differences among planting depths were found. During the dry summer, there was a positive relationship between increased planting depth and improved survivability of seedlings. In conclusion, deep planting improved growth of Norway spruce seedlings and was an advantage in dry conditions.

Cronartium flaccidum is an important pathogen in boreal forestry where it causes pine stem rust. The hemiparasite Melampyrum sylvaticum serves as a telial host for this heteroecious fungus while the congeneric M. pratense is highly resistant. We hypothesized that the variation in susceptibility is due to differences in the composition of secondary phenolic compounds in host plant tissues. To test this hypothesis, phenolic compounds of leaf extracts taken from both species of Melampyrum were analyzed with HPLC. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used for data processing. PCA indicated difference between the species, with the first two components explaining more than 70 % of the total variance of data that was separated into two distinct groups in a scatter plot. Two clusters, formed by the two species, were also suggested by HCA. Phenolic acids (such as chlorogenic acid), flavanones and apigenin flavonoids dominated the profiles of rust-resistant M. pratense, while kaempferol and luteolin flavonoids occurred in high relative concentrations in rust-susceptible M. sylvaticum. Our results suggest that phenolics may contribute to resistance or susceptibility of Melampyrum to Cronartium rusts as one factor. Future studies on the mode of action of phenolics in this interaction are thus warranted.

We studied long-term effects of fertilization with wood ash on biomass, vitality and mycorrhizal colonization of fine roots in three conifer forest stands growing in Vacciniosa turf. mel. (V), Myrtillosa turf. mel. (M) and Myrtillosa turf. mel./Caricoso-phragmitosa (MC) forest types on peat soils. Fertilization trials amounting 5 kg/m² of wood ash were established 12 years prior to this study. A total of 63 soil samples with roots were collected and analysed. Ectomycorrhizal (ECM) fungi in roots were identified by morphotyping and sequencing of the fungal internal transcribed spacer (ITS) region. In all forest types, fine root biomass was higher in fertilized plots than in control plots. In M forest type, proportion of living fine roots was greater in fertilized plots than in control plots, while in V and MC, the result was opposite. Fifty ECM species were identified, of which eight were common to both fertilized and control plots. Species richness and Shannon diversity index were generally higher in fertilized plots than in control plots. The most common species in fertilized plots were Amphinema byssoides (17.8 %) and Tuber cf. anniae (12.2 %), while in control plots, it was Tylospora asterophora (18.5 %) and Lactarius tabidus (20.3 %). Our results showed that forest fertilization with wood ash has long-lasting effect on diversity and composition of ECM fungal communities.

Alien invasive pathogens have caused numerous disastrous epidemics around the globe during the last two centuries. The frequency of these catastrophes has increased in parallel with the increase of international plant trade. Effective control of the risks requires understanding of factors governing vulnerability of indigenous plants. We tested whether the threat caused by alien pathogens of Asian origin is random among various tree species in Europe or whether it relates to their distribution range. A database including distribution ranges of 75 European tree species and literature-derived information on their susceptibility to invasive forest pathogens (IFPs) of Asian origin was compiled. Analysis on this database indicated that the susceptibility to Asian pathogens is significantly more common among tree species that occur only within Europe than among species with distributional ranges from Europe to Siberia (disease susceptibility percentage, DSP, 52 and 19 %, respectively). Notably, all severely attacked tree species are strictly European while tree species with distribution ranges extending from Europe to Siberia show at most only mild or moderate symptoms of Asian IFPs. Furthermore, the proportion of European broadleaf tree species susceptible to Asian IFPs is significantly higher than that of conifer species. Our results suggest that in Europe, Asian pathogens cause a higher risk to temperate and Mediterranean forests, largely composed of broadleaved species with distributional ranges restricted to Europe, than to boreal forests dominated by conifers distributed to Siberia.

We examined differences in fine root morphology, mycorrhizal colonisation and root-inhabiting fungal communities between Picea abies individuals infected by Heterobasidion root-rot compared with healthy individuals in four stands on peat soils in Latvia. We hypothesised that decreased tree vitality and alteration in supply of photosynthates belowground due to root-rot infection might lead to changes in fungal communities of tree roots. Plots were established in places where trees were infected and in places where they were healthy. Within each stand, five replicate soil cores with roots were taken to 20 cm depth in each root-rot infected and uninfected plot. Root morphological parameters, mycorrhizal colonisation and associated fungal communities, and soil chemical properties were analysed. In three stands root morphological parameters and in all stands root mycorrhizal colonisation were similar between root-rot infected and uninfected plots. In one stand, there were significant differences in root morphological parameters between root-rot infected versus uninfected plots, but these were likely due to significant differences in soil chemical properties between the plots. Sequencing of the internal transcribed spacer of fungal nuclear rDNA from ectomycorrhizal (ECM) root morphotypes of P. abies revealed the presence of 42 fungal species, among which ECM basidiomycetes Tylospora asterophora (24.6 % of fine roots examined), Amphinema byssoides (14.5 %) and Russula sapinea (9.7 %) were most common. Within each stand, the richness of fungal species and the composition of fungal communities in root-rot infected versus uninfected plots were similar. In conclusion, Heterobasidion root-rot had little or no effect on fine root morphology, mycorrhizal colonisation and composition of fungal communities in fine roots of P. abies growing on peat soils.