Eeva Terhonen

Diversity and Community Structure of Primary Wood-Inhabiting Bacteria in Boreal Forest

DNA-based pyrosequencing analysis of the V1- V3 16S rRNA gene region was used to identify bacteria community and shift during early stages of wood colonization in boreal forest soils. The dataset comprised 142,447 sequences and was affiliated to 11 bacteria phyla, 25 classes and 233 genera. The dominant groups across all samples were Proteobacteria, followed by Bacteroidetes, Acidobacteria, Actinobacteria, Amatimonadetes, Planctomycetes and TM7 group. The community structure of the primary wood-inhabiting bacteria differed between types of forest soils and the composition of bacteria remained stable over prolonged incubation time. The results suggest that variations in soil bacterial community composition have an influence on the wood-inhabiting bacterial structure.

Dominant Tree Species and Soil Type Affect the Fungal Community Structure in a Boreal Peatland Forest

ABSTRACT Boreal peatlands play a crucial role in global carbon cycling, acting as an important carbon reservoir. However, little information is available on how peatland microbial communities are influenced by natural variability or human-induced disturbances. In this study, we have investigated the fungal diversity and community structure of both the organic soil layer and buried wood in boreal forest soils using high-throughput sequencing of the internal transcribed spacer (ITS) region. We have also compared the fungal communities during the primary colonization of wood with those of the surrounding soils. A permutational multivariate analysis of variance (PERMANOVA) confirmed that the community composition significantly differed between soil types (P < 0.001) and tree species (P < 0.001). The distance-based linear models analysis showed that environmental variables were significantly correlated with community structure (P < 0.04). The availability of soil nutrients (Ca [P = 0.002], Fe [P = 0.003], and P [P = 0.003]) within the site was an important factor in the fungal community composition. The species richness in wood was significantly lower than in the corresponding soil (P < 0.004). The results of the molecular identification were supplemented by fruiting body surveys. Seven of the genera of Agaricomycotina identified in our surveys were among the top 20 genera observed in pyrosequencing data. Our study is the first, to our knowledge, fungal high-throughput next-generation sequencing study performed on peatlands; it further provides a baseline for the investigation of the dynamics of the fungal community in the boreal peatlands.

High infection rate of residual conifer stumps by Heterobasidion species in an area with assumed low infection pressure

Abstract The study was made in order to assess the infection rate of conifer stumps by Heterobasidion species in transition zone between southern boreal and middle boreal areas. Majority of surveys of stump infection rate have been made in areas where the fungus is already a considerable problem; typically the effective temperature sum in these areas exceeds 1200 degree days (d.d.). In the study, the incidence of stump infection was surveyed by intensive sampling of cut stump surfaces in the Central Finland in area where the temperature sum is 1100 d.d. and sporadic observations of damages caused by H. annosum s.l. have been made. Residual stumps were surveyed in total of 31 sites where majority of stumps had been harvested. Of those, 24 (75%) were infected. The stump infection rate was less than 20% on most sites. On average, 13% of spruce stumps were infected. The frequency of infected stumps varied considerably between the studied stands. The infection percentage of residual stumps in stump harvesting areas was corresponding to that obtained from earlier studies. Our results demonstrate that although the stump harvesting effectively decreases the number of infected stumps, the stumps left after summer cutting on the clear-cut area may be an additional infection pathway. No clear linear trend between mean temperature and proportion of infected stumps could be found.

Comparative analyses of fungal biota carried by the pine shoot beetle (Tomicus piniperda L.) in northern and southern Finland

The pine shoot beetle, Tomicus piniperda, is a secondary colonizer of pines and other conifers. Although it is necessary to understand interactions of this insect with other organisms, few studies have focused on its fungal associates. This study focused on the effect of geographical distance on the occurrence of fungi carried by the beetle. Adult beetles were collected from Scots pine (Pinus sylvestris) in North (Rovaniemi) and South (Hyytiälä) Finland. The mycota was isolated and identified using a combination of morphological and molecular data. The results revealed a great diversity of fungal taxa isolated from T. piniperda, with a total of 3073 isolates representing 20 taxonomic units. The most frequently isolated fungi in the bark beetles from North Finland were Beauveria bassiana, Kuraishia sp., whereas Penicillium velutinum was mostly observed in the insects from South Finland. Ophiostoma canum and Ophiostoma minus were also isolated from the beetles from both North and South Finland. The number of fungi isolates per insect was 2.58 in the North and 3.74 in the South, respectively. Significant differences were found between South and North Finland in fungal taxa isolated from the beetles. The highest richness and diversity of the fungal taxa was observed in the South. However, the overall fungal diversity index analysis revealed that the mycobiota was under-sampled which suggests that a proportion of the fungal species may have remained undetected.