Decomposition and Pedogenesis

I. Types and Patterns of Detritivory and Burrowing

A. Detritivore and Burrower Functional Groups

B. Measurement of Detritivory, Burrowing, and Decomposition Rates

C. Spatial and Temporal Patterns in Processing of Detritus and Soil

II. Effects of Detritivory and Burrowing

A. Decomposition and Mineralization

B. Soil Structure, Fertility, and Infiltration

C. Primary Production and Vegetation Dynamics

III. Summary

DECOMPOSITION IS THE BREAKDOWN OF DEAD ORGANIC MATTER THAT eventually results in release of CO2, other organic trace gases, water, mineral nutrients, and energy. Pedogenesis (soil development) largely reflects the activities of animals that mix organic matter with mineral soil. These two processes contribute greatly to the capacity of a site to support primary production. Accumulated organic litter represents a major pool of energy and nutrients in many ecosystems. Carbon and other nutrients released through decomposition can be acquired by plants or microbes or returned to abiotic pools (see Chapter 11). Incorporation of decay-resistant organic matter and nutrients into soil increases fertility, aeration, and water-holding capacity. Release of CO2, CH4, and other trace gases affects atmospheric conditions and global climate.

Decomposition can be categorized into four component processes: photooxi-dation, abiotic catabolism resulting from exposure to solar radiation; leaching, the loss of soluble materials as a result of percolation of water through material; comminution, the fragmentation of organic litter, largely as a result of detritivory; and mineralization, the catabolism of organic molecules by microorganisms. Vossbrinck et al. (1979) found that when arthropods and microbes were excluded, detritus lost only 5% mass, due entirely to leaching or photooxidation. A variety of macroarthropods, mesoarthropods, and microarthropods are the primary detritivores in most ecosystems. The feeding and burrowing activities of many animals, including ants, termites, and other arthropods, redistribute and mix soil and organic material. Burrowing also increases soil porosity, thereby increasing aeration and water-holding capacity.

The effects of arthropod detritivores and burrowers on decomposition and soil development have been the most widely studied effects of arthropods on ecosystem processes (e.g., Ausmus 1977, Coleman et al. 2004, Crossley 1977,

Eldridge 1993,1994, Seastedt 1984, Swift 1977, Swift et al. 1979, Whitford 2000, Wotton et al. 1998). Arthropod detritivores and burrowers are relatively accessible and often can be manipulated for experimental purposes. Their key contributions to decomposition and mineralization of litter (both fine or suspended organic matter and coarse woody debris) and pedogenesis have been demonstrated in virtually all ecosystems. Indeed, some aquatic and glacial ecosystems consist of arthropod detritivores and associated microorganisms feeding entirely on allochthonous detritus (J. Edwards and Sugg 1990, Oertli 1993, J. Wallace et al. 1992). Effects of detritivorous and fossorial species on decomposition and soil mixing depend on the size of the organism, its food source, type and rate of detritivory, volume of displaced litter or soil, and type of saprophytic microorganisms inoculated into litter. Although most studies have addressed the effects of detritivores and burrowers on soil processes, some have documented effects of animal contributions to soil development and biogeochemical cycling to primary production as well.

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