Microbial Response to Charcoal Amendments and Fertilization of a Highly Weathered Tropical Soil

Charcoal is a major component of stable SOM in terras pretas alsocalled Amazonian Dark Earths (Glaser et al. 2001a, b; Glaser 2007). Apart from charcoal, special microbes could contribute to the formation of the highlystable SOM in terra preta (Woods and McCann 1999). However, this is stillmatter of speculation. There could be a link between the high amounts of charcoal in terra preta soils and soil microbial community composition (Glaser 2007). Although it is unlikely that charcoal is used by microorganisms as a direct carbon source, habitat properties are certainly different with the presence or absenceof charcoal (Saito and Marumoto 2002). Steiner et al. (2004) could demonstrate that charcoal addition to Ferralsols significantly increased microbial activity. Charcoal also promoted the colonization of agricultural plants with arbuscular mycorrhizal fungi (Nishio 1996; Saito and Marumoto 2002), it improved nodule weight (Nishio 1996) and nitrogen fixation (Tryon 1948; Nishio 1996; Rondon et al. 2007).

Most soil microorganisms cannot be characterized by conventional cultivation techniques (Zelles 1999). Amann et al. (1995) estimated that 80–99% of all micro-bial species have not yet been cultured. Therefore, biomarkers such as ribosomal nucleic acids (RNA) or phospholipid fatty acids (PLFA) are better analytical tools to provide an unbiased view on the structure of complex soil microbial communities (Zelles 1999). PLFA are exclusively found in the membranes of living organisms and comprise a relatively constant portion of living biomass within a microbial community (Zelles 1999). The analysis of PLFA allows the simultaneous quantification of microbial biomass and the characterization of the microbial community structure by specific biomarker PLFA (Tunlid and White 1992; Zelles 1999; Gattinger 2001).