The microbial world of terra preta

ADE sites vary in their size and degree of engineering (Woods and McCann 1999), and their biochemistry may be influenced by the addition of any of the following: large amounts of pottery sherds, concentrated organic wastes, charred biomass, fish bones, shells, various household wastes. In many ADE these additions have resulted in notably high nutrient concentrations of calcium, phosphorus, and potassium, and also high levels of black carbon (BC). The latter is thought to play a key role in greater nutrient retention and stabilization of soil organic matter, as decomposing residue or within living cells (Glaser et al. 2003; Sombroek et al. 2003), in spite of intense weathering conditions which typically lead to highly leached soils in the humid tropics (Lehmann et al. 2003). Thus the central role of the soil microbial community is in this unique soil environment should be traced to soil amendments such as BC. Black C is not unique to ADE, but occurs throughout terrestrial and aquatic environments (Schmidt and Noack 2000) as residue from naturally-occurring and human-induced burning. Once created, BC persists over time-scales of millennia and is thought be highly recalcitrant to microbial degradation (Schmidt and Noack 2000). In soil, BC may enhance soil fertility by decreasing bulk density, improving moisture retention and increasing pH, and the surface charge properties of BC are thought to increase cation exchange capacity (CEC), thereby reducing nutrient leaching (Glaser et al. 2002). The anthropic addition of BC to ADE may help stabilize inorganic nutrients and thus maintain soil fertility (Glaser et al. 2003), however, it may also serve directly as a habitat or as a platform for nutrient exchange for microorganisms (Abu-Salah et al. 1996 Chitra et al. 1996). High BC additions to soil due to fire events in northern boreal forest, have been shown to alter soil microbiological community structure and above ground plant communities (Pietikainen et al. 2000; Zackrisson et al. 1996), but little other research exists on the impact of BC on below-ground biological communities. Due to its prevalence in ADE and its unique physical and chemical characteristics, BC is thought to be central to the biogeochemistry of these soils.