Decomposer Organisms
Litter is mainly degraded by microorganisms (fungi and bacteria) and in boreal coniferous systems this is emphasized. The degradation of lignin is carried out by aerobic organisms (mainly white-rot but also soft-rot and brown-rot) whereas the degradation
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Decomposer Organisms
Abstract Litter is mainly degraded by microorganisms (fungi and bacteria) and in boreal coniferous systems this is emphasized. The degradation of lignin is carried out by aerobic organisms (mainly white-rot but also soft-rot and brown-rot) whereas the degradation of cellulose and hemicelluloses proceeds under both aerobic and anaerobic conditions. The main enzymatic processes are described as well as factors that influence the formation and production of enzymes in microorganisms. The characteristics of white-rot, brown-rot and soft-rot are reviewed. The repression caused by N on formation and activity of the lignin-degrading enzyme system is discussed as is the role of Mn for the formation of the widespread enzyme manganese (Mn) peroxidase. The potential importance of mycorrhizal fungi in humus degradation is introduced and the need for a better understanding of microbial ecology combined with new molecular biology approaches relative to decomposition processes is emphasized.
3.1 Introduction The dominant primary decomposers in boreal and temperate forest soil systems are the microorganisms, encompassing both fungi and bacteria. Both these main groups of microorganisms can degrade cellulose, hemicellulose, and the different lignins. This chapter will emphasize the functional roles of organisms (e.g., cellulolytic and ligninolytic) rather than their taxonomy. The concepts white-rot, brown-rot, and softrot and what they stand for functionally in terms of degradation processes will be presented. Many microorganisms degrade cellulose and hemicellulose in nature. These organisms have in common the production of extracellular hydrolytic enzymes that are either bound onto the outside of the cell or released into the surrounding environment. Polymer carbohydrates may be degraded both aerobically and anaerobically, but a complete degradation of lignin (white-rot type) requires the action of aerobic organisms (fungi and/or aerobic bacteria). Partial lignin degradation (brown-rot type) may also be carried out by anaerobic bacteria, but is mainly found among fungi and aerobic bacteria.
© Springer Nature Switzerland AG 2020 B. Berg and C. McClaugherty, Plant Litter, https://doi.org/10.1007/978-3-030-59631-6_3
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3 Decomposer Organisms
We have used the functional concepts white-rot, brown-rot, and soft-rot as a basis for the discussion of degradation of litter. Although the terms originally seem to refer to visually different types of lignin degradation, it now appears that the degradation of cellulose and hemicellulose is also different among the groups (Worrall et al. 1997). The terms refer to the type of rot rather than to a group of organisms, but we have adopted the common use of the terms and refer to fungi when using the terms white-rot, brown-rot, and soft-rot. As regards degradation by bacteria, it is described and discussed as such. The composition of the microbial population (e.g., cellulolytic vs. ligninolytic) may vary with general properties of the soil/litter ecosystem, such as nut
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