In contrast to energy, which is ultimately lost from an ecosystem as heat, nutrients continually cycle between living organisms and the abiotic components of ecosystems (see Figure 57.1C). Organisms require 30–40 different nutrients, including the macronutrients carbon, hydrogen, nitrogen, calcium, phosphorus, potassium, and magnesium, and micronutrients such as iron, manganese, zinc, and copper. All the chemical components in the bodies of organisms ultimately originate from soil, water, or the atmosphere, but organisms acquire these materials in many different ways. Autotrophs such as plants take up certain elements directly from soil, water, and the atmosphere and incorporate them in their tissues. Heterotrophs generally acquire elements by consuming the biomass of other organisms, and then reassemble them via chemical reactions. Some heterotrophs acquire some elements from mutualistic microbes that convert them into forms that are usable by their hosts.
Gas exchange by living organisms returns certain elements to the atmosphere as gases. After organisms die, the materials in their bodies become detritus and are broken down by decomposers into simpler biochemical components, which then can be used by autotrophs once again. Elements not used by autotrophs can accumulate in soil, water, or sediments.