A reviewon the methods for measuring total microbial activity in soils

Total microbial activity( TMA) in soils is vital for understanding the roles of microorganisms in ecosystem processes. It can be defined as the sum of physiological activities of all the microbes at a given moment. As TMA is difficult to measure directly,a series of proxies,such as respiration rates,growth rates,and cellular RNA concentration,have been proposed. Here,methods used to measure soil TMA are synthesized and compared.( 1) Respiration may be the process most closely related to life activities. Thus,respiration rates are the most commonly used proxies of soil TMA. The main limitation is that current methods to determine respiration rates usually cannot accurately reflect actual respiration rates.When respiration rates are measured using CO_2 production or O_2 consumption rates,they indicate carbon mineralization or aerobic respiration rates,respectively.( 2) Microbes with higher growth rates are usually more active. Thus,growth rates are also widely used to indicate soil TMA. As biomacromolecule synt