Biogeochemistry 11: 153-174, 1990 © Kluwer Academic Publishers. Printed in the Netherlands Litter decomposition: a Russian matriochka doll H. EIJSACKERS' & A.J.B. ZEHNDER 2 'The Netherlands Integrated Soil Research Programme, P.O. Box 37, 6700 AA Wageningen; 2 Department of Wageningen Agricultural University, P.O. Box 8033, 6700 EJ Wageningen The Netherlands Received 3 December 1989; accepted 23 July 1990 Key words: litter decomposition, fragmentation, mineralization, humus formation, organic matter, soils and sediments Abstract. Litter is decomposed in a sequential process. In a concerted action animals and microor- ganisms break down complex organic matter to mineral products. Higher animals fragment and partially solubilize plant material. Subsequently, microorganisms (protozoa, fungi and bacteria) further degrade the organic matter to end products that cannot be metabolized further under the prevailing environmental conditions. During the process of decomposition some parts of the organic substrate and the excess energy are used to form new biomass. Some free organic intermediates may interact chemically to form relatively recalcitrant organic matter, such as humic substances. The degree of mineralization depends strongly on the type of organic matter in the litter and the physical and chemical conditions of the environment. 1. Introduction At a distance litter decomposition seems to be one process. However, closer examination reveals a variety of different processes nested in each other, like nesting Russian dolls. If the basic principles of this sequence are understood we may be able to predict the fate of a given compound in a specific environment. An understanding of the kinetics of decomposition processes is critical for the management and control of the organic matter content in various soils under different climatic conditions. Below, we will briefly define the types of organic matter in litter, before discussing the various distinct processes that are involved in the mineralization of litter. Then, the principles of humic matter formation will be summarized very briefly. We propose to discuss the environmental influences on litter decomposition in general terms only, since other chapters will deal with it in more detail. All this information will be combined to describe quantitatively the fate of litter in soil and sediments. Finally, we will try to show the implications of present knowledge of litter decomposition for future soil management. 2. Types of organic matter in litter Soil scientists have paid much attention to the composition of sections of soil, especially the organic horizons (Verhoef & Brussaard, this issue) and have spent