Soils as extended composite phenotypes

Several recent theories and conceptual frameworks in pedology, ecology, geomorphology, and evolutionary biology, taken together, suggest the notion that earth's soils are not just strongly influenced by biota, but represent selective pressures. These ideas point in the direction of many aspects of soils as expressions of the effects of genes through the effects of organisms (i.e., extended phenotypes). The cumulative, interacting, overlapping effects of these extended phenotypes as manifested in the soil represent an extended composite phenotype. If this is the case, then we should expect major changes in biological evolution to be reflected in major changes in the types of soils. A brief review of paleopedology literature supports the notion of coevolution of soils and biota, not just in the sense of both responding to the same environmental forcings, but also with respect to explicit pedological expressions of biological change. The extended composite phenotype notion also suggests that significant biological changes should be reflected in significant qualitative pedological changes (i.e., fundamental changes in soil morphology beyond quantitative changes in specific short-lived soil properties). This is demonstrated via recent research in the Ouachita Mountains, Arkansas, where changes in selective pressures on trees associated with fire frequency are linked to changes in soil morphology. The concept of soils as extended composite phenotypes has repercussions for pedology, evolutionary biology, and interpretations of soils in other earth and environmental sciences. The notion of genetic signatures in soil morphology also has implications for the search for extraterrestrial life, and extends the notion of Earth as a set of tightly-coupled, densely interwoven systems.