ABSTRACT
The way in which ecosystems use energy to power their functioning was analysed in Chapter 3. The transmission of energy through an ecosystem is dependent on the availability of specific materials. A central feature of all material use in ecosystems is cycling. Without cycling, ecosystem functioning would rapidly come to a halt. This chapter is concerned with not only what materials are involved in ecosystem function, and their specific functional roles, but also the ways in which different ecosystem materials are constantly cycled within the biosphere. General types of cycling systems which are based on particular nutrient elements can be defined. However, the detailed pattern of nutrient use and cycling within an ecosystem depends on the specific character of that ecosystem, in particular the nature of autotrophic vegetation and primary production in that ecosystem, and the characteristics of the physical environment. In the analysis of material cycles in ecosystems the biological focus will be on two categories of organisms, autotrophs and detritivores. The former are responsible for the intake of mineral nutrients into the ecosystem, and thus for virtually all the material flow in the living components of the ecosystem, while the latter breakdown organic tissue, returning partly or wholly disaggregated material to the soil in the case of terrestrial environments. The former use nutrients to construct the substance of life, the latter are a major factor in the return of living material to a simple abiotic form, which can be used again by plants.
