Biological Strategies of Nutrient Cycling in Soil Systems

1. A thorough knowledge of physics, chemistry, and biology of soil-related processes is essential for understanding terrestrial ecosystem function. We show how soil characteristics on a macro-scale in a landscape (catena), and on a micro-scale in a soil aggregate must be considered in ecosystem studies. 2. After reviewing aspects of soil chemistry, biochemistry, and development, a detailed review of biotic interactions (principally microbial-plant, microbe-microbe, and microbe-fauna)is presented. Much of our information to date is derived from laboratory process studies, and the need for more controlled field experiments is emphasized. 3. The strong driving force of interactions, chemical and biological, at the soil-root interface, is emphasized. These include direct trophic interactions, and enzymatic, as well as possible hormonal influences. There is a great need for an adequate analysis of biotic interactions in the extremely heterogeneous soil matrix. 4. We examine ecological concepts of stability and resilience, in relation to food-web complexity and nutrient cycling. It is apparent that ecosystem stability in relation to nutrient cycling involves different sorts of pools: those which are small, turning over rapidly, and principally microbe-fauna mediated; and others which are very large, non-labile, and turning over slowly, in a few to several centuries