The habitat of the soil biota

Soil is a habitat for the biota that regulate the functioning of terrestrial ecosystems and have a central role in controlling the Earth’s environment. The soil biota are responsible for the dynamics of the constituents of soil organic matter, thereby promoting nutrient cycling and greenhouse gas emissions. The habitat provided by the soil is characterized by heterogeneity, measured across scales from nanometers to kilometers, and differs in chemical, physical, and biological characteristics in both space and time. The nature of the habitat is determined by the intensity of the interaction of geology, climate, and vegetation and is a biochemical product of the organisms participating in its genesis. The soil resource has been widely exploited for the production of food and fiber. This has resulted in severe degradation of the soils’ physical, chemical, and biological properties that control the functioning of these ecosystems, the most critical being loss of biodiversity of the biota living within the soil. Nevertheless, soils provide a tremendous range of habitats that support enormous biota biomass globally and harbor much of the Earth’s genetic diversity. Soil organisms are primarily located in hotspots on the surfaces of soil particles, plant litter, and rhizosphere, where nutrients are most concentrated. While the main soil properties influencing the gross behavior and activity of soil organisms within the bulk soil matrix are known (i.e., water and aeration, temperature, and nutrient availability), the principles, processes, and consequences of the distribution of soil properties at the microscale have traditionally been outside of the focus of soil scientists and ecologists and remain underinvestigated. This chapter presents a review of the physical, chemical, and biological properties that define the soil habitat across macro- to microscales.