Scaling microbial biomass, metabolism and resource supply

The microbiome concept has drawn attention to the complex signal and syntrophic networks that underlie microbial community organization. This self-organization may lead to patterns in the allometric scaling of microbial community metabolism that differ from those of macrobial communities. Using meta-analyses, we analyzed the power scaling relationships between community production, respiration, extracellular enzyme activity and biomass for bacteria and fungi across aquatic and terrestrial ecosystems. The scaling exponents for community production versus biomass for fungi and bacteria were 0.85 +/- A 0.06 (95 % CI) and 0.72 +/- A 0.07, respectively. The scaling exponent for fungal respiration versus production was 0.61 +/- A 0.06. Previous studies reported exponents of 0.41, 0.44 and 0.58 for bacterial respiration versus production. Carbon use efficiency increased with biomass for both fungi and bacteria with an exponent of 0.27 +/- A 0.06. The potential activities of four widely measured extracellular enzymes were directly related to community production with power scaling exponents of 1.0-1.2. The frequency distribution of biomass turnover times (median 112 h for bacteria and 1,128 h for fungi) overlapped substantially with those for environmental substrate turnover, presented in a prior analysis of extracellular enzyme kinetics. These metabolic relationships, which have scaling exponents of 0.5, are linked by the ratio of assimilation to carbon use efficiency. This connection ties ecological stoichiometry and metabolic theory to microbial community homeostasis. At the ecosystem scale, allometry of microbial communities has similarities to that of eusocial insects but differs from that of plant communities, perhaps as a result of proto-cooperative processes that contribute to microbial community organization.