For the last several decades, there has been interest in the role of soil fauna in litter and organic matter turnover in ecosystems. The pioneering studies of Darwin (1881) and P. E. Müller (1887) emphasized the prominent signs left in many temperate forest and grassland communities by earthworm, mesofauna, and biotic activities in general. A very prescient account of the "biotic" structure of soils was given by Jacot (1936). Signs of faunal activity include coating of mineral grains, which has a significant effect on promoting the formation of aggregates (Kubie-na, 1938). Termites in semitropical and tropical regions have similar functions as well (e.g., Lee and Wood, 1971; Wood et al., 1983). Only a few ecologists are aware, however, that often the soil meso- and microfauna are vastly more numerous—and usually more active in terms of respiratory activity—than the large soil fauna (Wolters, 1991; Coleman, 1994, 2001).
Our concerns as ecosystem researchers should include both an understanding of which organisms are present and the major processes that they carry out in a wide range of terrestrial ecosystems. Following the flow of energy and nutrients in the system (as noted by Volobuev, 1964) will enable us to concentrate on key processes that occur, avoiding the pitfall of what is obvious to the naked eye being singled out for study. We must get to the appropriate level of resolution to ascertain the roles of participants in soil processes (Macfadyen, 1969; Coleman, 1985). This requires exploring the myriad of surfaces and volumes that occur in a few cubic millimeters of soil and organic matter (Elliott, 1986; Elliott and Coleman, 1988).
Fauna are members of the "organism" category in Jenny's (1941) factors of soil formation (recall from Chapter 1 [Fig. 1.5]: soil = f (cl, o, r, p, t), where cl = climate, o = organisms, r = relief, p = parent material, and t = time). As noted by Crocker (1952), only a few of these factors are independent variables, so we are dealing with a multicause, interdependent subset of a terrestrial ecosystem. To simplify matters, let us consider organisms alone, that is, vegetation, organic matter inputs therefrom, andthe array of heterotrophic organisms feeding upon and decomposing
Role of Soil Fauna in Organic Matter Dynamics and Nutrient Turnover
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