Adenylate energy charge (AEC) in soil: an almost ignored determination of soil microbial activity - in memory of Phil Brookes

The current opinion paper aims to revitalize the important methodological approach initiated by Phil Brookes to measure the adenylate energy charge (AEC) of soils, which indicates the energy status of microbial biomass carbon (MBC). Even dormant soil microorganisms maintain high AEC, i.e., (ATP + 0.5 × ADP) / (ATP + ADP + AMP), levels and, thus, rather stable ATP/MBC and adenylate/MBC ratios. New extractants, improved enzymatic tests, and chromatographic systems are available now that could give new impetus to the measurement of adenylates and AEC in soil. The AEC is a useful tool to investigate important and still unsolved questions in soil microbial biochemistry. For example, drying and rewetting cycles of soil lead to AEC fluctuations, where the energy fluxes of ATP hydrolysis and synthesis remain unknown. Decreasing AEC values might give insights into microbial death processes, particularly in combination with amino sugar assays or molecular genetic techniques.