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> Abstract The structure, biomass, and activity of the microbial community in the humus layer of boreal coniferous forest stands of different fertility were studied. The Scots pine dominated CT (Calluna vulgaris type) represented the lowest fertility, while VT (Vaccinium vitis-idaéa type), MT (Vaccinium myrtillus type), and OMT (Oxalis acetocella-Vaccinium myrtillus type) following this order, were more fertile types. The microbial community was studied more closely by sampling a succession gradient (from a treeless area to a 180-years-old Norway spruce stand) at the MT type site. The phospholipid fatty acid (PLFA) analysis revealed a gradual shift in the structure of the microbial community along the fertility gradient even though the total microbial biomass and respiration rate remained unchanged. The relative abundance of fungi decreased and that of bacteria increased with increasing fertility. The structure of the bacterial community also changed along the fertility gradient. Irrespective of a decrease in fungal biomass and change in bacterial community structure after clear-cutting, the PLFA analysis did not show strong differences in the microbial communities in the stands of different age growing on the MT type site. The spatial variation in the structure of the microbial community was studied at a MT type site. Semivariograms indicated that the bacterial biomass, the ratio between the fungal and bacterial biomasses, and the relative amount of PLFA 16:1omega5 were spatially autocorrelated within distances around 3 to 4 m. The total microbial and fungal biomasses were autocorrelated only up to 1 m. The spatial distribution of the humus microbial community was correlated mainly with the location of the trees, and consequently, with the forest floor vegetation.http://link.springer-ny.com/link/service/journals/00248/bibs/38n2p168.html

The scaling up of the pressurized hot water flow-through extraction system for sawdust by a factor of 6000.

Tannins, an abundant group of plant secondary compounds, raise interest in different fields of science, owing to their unique chemical characteristics. In chemical ecology, tannins play a crucial role in plant defense against pathogens, herbivores, and changing environmental conditions. In the food industry and in medicine, tannins are important because of their proven positive effect on human health and disease treatment. Such wide interests fueled studies on tannin chemistry, especially on their flagship ability to precipitate proteins. In this Review, we expand the basic knowledge on tannin chemistry to the newest insights from the field. We focus especially on tannin reactions with different non‐protein organic N compounds, as well as the complex interactions of tannins with enzymes, resulting in either an increase or decrease in enzyme activity.

Two major groups of plant secondary compounds, phenolic compounds and terpenes, may according to current evidence mediate changes in soil C and N cycling, but their exact role and importance in boreal forest soils are largely unknown. In this review we discuss the occurrence of these compounds in forest plants and soils, the great challenges faced when their concentrations are measured, their possible effects in regulating soil C and N transformations and finally, we attempt to evaluate their role in connection with certain forest management practices. In laboratory experiments, volatile monoterpenes, in the concentrations found in the coniferous soil atmosphere, have been shown to inhibit net nitrogen mineralization and nitrification; they probably provide a C source to part of the soil microbial population but are toxic to another part. However, there is a large gap in our knowledge of the effects of higher terpenes on soil processes. According to results from laboratory experiments, an important group of phenolic compounds, condensed tannins, may also affect microbial processes related to soil C and N cycling; one mechanism is binding of proteins and certain other organic N-containing compounds. Field studies revealed interesting correlations between the occurrence of terpenes or phenolic compounds and C or net N mineralization in forest soils; in some cases these correlations point in the same direction as do the results from laboratory experiments, but not always. Different forest management practices may result in changes in both the quantity and quality of terpenes and phenolic compounds entering the soil. Possible effects of tree species composition, clear-cutting and removal of logging residue for bioenergy on plant secondary compound composition in soil are discussed in relation to changes observed in soil N transformations.

In conifers, attacks by bark beetles and associated pathogenic fungi cause an induced wound response, which is characterized by accumulation of antifungal compounds and morphological changes that aid wound healing. In this article the stilbene and terpene concentrations of Norway spruce phloem were monitored as symptoms of induced wound responses in relation to changed nutrient conditions caused by fertilization. Plots of mature Norway spruce were fertilized with N, P or NPK. One year after fertilization the trees were artificially infected with Ceratocystis polonica, a pathogenic fungus associated with the bark beetle Ips typographus. The response of stilbenes to fungal inoculation was mainly qualitative. The concentration of stilbene glycosides in the phloem decreased, and in the immediate vicinity of the site of fungal inoculation, stilbene glycosides were less frequent than in mechanically wounded or unwounded phloem. Corresponding stilbene aglycones were most frequent inside the reaction lesion. The concentration of total stilbene aglycones near the inoculation site was significantly lower in N-fertilized trees than in unfertilized trees. Fungal inoculation caused a strong quantitative response in terpenes. The total terpene concentration of the phloem increased significantly, to almost 100 times greater near the inoculation site compared to the constitutive values. N fertilization significantly reduced the total terpene and total stilbene aglycone concentrations near the inoculation sites. Thus, N fertilization may reduce the ability of Norway spruce to defend itself against fungal pathogens.

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