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Enzymes in Forest Soils Petr Baldrian and Martina Sˇtursova´

4.1

Introduction

Forest soils typically accumulate dead organic material, known as plant litter, on the soil surface. When fresh, this material contains a variety of substrates, such as soluble saccharides, organic acids, amino acids or starch, as well as the plant cell wall-derived biopolymers, cellulose, hemicelluloses and lignin, which are utilized during the growth of soil decomposer microorganisms. The sequential transformation of plant litter in temperate forests leads to the formation of a distinct organic horizon derived from the transformation products of litter decomposition as well as the dead biomass of soil microorganisms. The organic horizon is known for its high content of humic substances. Compared to agricultural soils and grassland soils, forest soils contain more fungal biomass (van der Wal et al. 2006), and the mycorrhizal community is formed mainly by the ectomycorrhizal fungi associated with tree roots instead of the arbuscular mycorrhizal fungi, which dominate the grasslands. Due to the high input of organic matter, enzymes participating in the decomposition of organic matter play an important role in forest soils. The enzymes relevant to decomposition studies are those related to the degradation of plant cell wall polymers (cellulose, hemicellulose, lignin, pectin) and microbial biomass (chitin and other polysaccharides). Besides these, enzyme systems involved in the acquisition of nitrogen, phosphorus, and sulfur are also of interest because these elements are indispensable for the growth of soil microbial biomass. Plant litter decomposition is actually the most important process in shaping the formation of the soil matter gradient. This complex process involves numerous taxa of decomposer microorganisms and a wide array of enzymatic transformations of

P. Baldrian (*) and M. Sˇtursova´ Laboratory of Environmental Microbiology, Institute of Microbiology of the ASCR, v.v.i, Vı´denˇska´ 1083, Praha 4 14220, Czech Republic e-mail: [email protected]

G. Shukla and A. Varma (eds.), Soil Enzymology, Soil Biology 22, DOI 10.1007/978-3-642-14225-3_4, # Springer-Verlag Berlin Heidelberg 2011

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P. Baldrian and M. Sˇtursova´

individual molecules. It has been described as a successional process, where the initial chemical composition defines the microbial community which, in turn, secretes degradative enzymes. The produced enzymes change the chemical properties of the substrate. These changes further drive the decomposer community succession in the litter (Sinsabaugh et al. 2002a). In this chapter, factors affecting the activity of enzymes in forest soils with respect to their spatial distribution are discussed. The lignocellulose-degrading enzymes and their producers are the subject of another chapter in this book (Chap. 9).

4.2

Distribution of Enzymes in the Soil Profile

The stratification of organic compounds due to their sequential transformation by decomposer microorganisms leads to the formation of a sharp gradient o