Fungi to bacteria ratio: Historical misinterpretations and potential implications

Bacteria and fungi are the primary consumers and, thus, the decomposition pathways are described accordingly as bacterial-based or fungal-based energy channels. However, the fungi to bacteria ratios (F: B), which indicated either by microbial biomass, respiration, or growth, represents only a snapshot of the whole energy channel during a given period rather than the cumulative contribution. Even the energy channel biomass only takes into account one dimension without considering the time. We believe that the F: B ratio has been misinterpreted in an ecological sense due to a lack of a clear definition. Here, we estimated the F: B biomass ratios, production ratios (microbial biomass multiplied by the turnover rate) and assimilation ratios (the sum of microbial production and respiration) using a dataset from 192 relevant studies. The F: B biomass ratios varied from 0.106 to 9.080, depending on the methods used. Based on direct microscopy method, the fungal/(fungal + bacterial) production and assimilation ratios ranged from 0.39 to 54.78% and 0.25–45.05%, respectively; while, those ratios based on phospholipids fatty acids (PLFAs) method were 0.06–5.51% and 0.04–0.66%, respectively. We conclude that bacteria contributes greater to the energy flow in terrestrial ecosystems compared with fungi based on the F: B assimilation. The relative contribution of bacteria and fungi can be better evaluated using the F: B assimilation ratio, rather than the biomass ratio or production ratio. Nevertheless, there are still uncertainties in the estimations of microbial production and assimilation due to their complicated responses to soil fauna activities. The regulation of soil fauna on microbial biomass, turnover rate and respiration, and associated changes in the energy allocations in the soil food web should be emphasised in future studies.