Microbial biomass estimation by fumigation extraction and ATP – A review in memoriam of Phil Brookes

Abstract Microbial biomass is a key feature of soils and gives information on energy and nutrient storage in the living and potentially active soil pool. The main two methods used by Phil Brookes were fumigation extraction (FE) and the adenosine triphosphate (ATP) assay. Today, the FE method dominates the estimation of microbial biomass carbon (MBC), whereas ATP is rarely measured. The aim of this review is to show actual and future directions in the use of fumigation extraction and to revitalize the measurement of ATP and adenylates as an important alternative to the FE method. The current review gives information on the principle, the advantages and disadvantages of these two approaches. The enzymatic ATP determination in trichloroacetic acid (TCA) extracts, where the toxic paraquat was replaced by imidazole, resulted in a weighted median of 9.6 µmol ATP g −1 MBC, based on 61 observations in 15 studies. A re-assessment of the ATP/MBC and adenylates/MBC ratios obtained by a high-performance liquid chromatography (HPLC) technique resulted in median concentrations of 5.8 µmol ATP and 8.6 µmol adenylates g −1 MBC, respectively, obtained from 165 samples in 21 studies. The FE method will maintain its importance, as it allows direct access to virtually all elements and organic components stored as CHCl 3 -labile compounds. For measuring ATP and adenylates, new extractants, improved enzymatic tests, and simpler HPLC systems are available now. Consequently, the assessment of ATP and also adenylates may be an important alternative as a cheap, rapid, and sensitive method, particularly for determining MBC in low organic matter soils.