Vertical Distribution of Soil Pyrogenic Matter: A Review

Alteration of terrestrial biomass during fire produces pyrogenic matter, a large quantity of which is deposited on and may enter soils. The amount of annual burning around the globe implies greater production and storage of carbon in soil pyrogenic organic matter (pyrOM) than is regularly found in investigations of soil pyrogenic matter. A portion of this unaccounted for pyrogenic material may be translocated to subsurface soil depths, which is frequently excluded from soil investigations, and the presence of subsoil charcoal helps to partially fill this pyrOM gap. In this paper, I discuss the mechanisms for vertical redistribution of pyrogenic matter in soils and develop conceptual models to describe the depth, particle size, and age distribution of pyrogenic matter resulting from different translocation mechanisms. Based on the relationships between pyrogenic matter turnover and translocation, the suitability of pyrogenic matter in soils as an indicator for soil processes is discussed. Deciphering the relationships between pyrogenic matter depth, particle size, and age distribution yields valuable insights into the dynamics of soil forming processes as well as soil pyrogenic matter turnover, which should therefore, be a focus of future studies.