Differences in fungal and bacterial physiology alter soil carbon and nitrogen cycling: insights from meta-analysis and theoretical models

Since fungi and bacteria are the dominant decomposers in soil, their distinct physiologies are likely to differentially influence rates of ecosystem carbon (C) and nitrogen (N) cycling. We used meta-analysis and an enzyme-driven biogeochemical model to explore the drivers and biogeochemical consequences of changes in the fungal-to-bacterial ratio (F:B). In our meta-analysis data set, F:B increased with soil C:N ratio (R2=0.224, P<0.001), a relationship predicted by our model. We found that differences in biomass turnover rates influenced F:B under conditions of C limitation, while differences in biomass stoichiometry set the upper bounds on F:B once a nutrient limitation threshold was reached. Ecological interactions between the two groups shifted along a gradient of resource stoichiometry. At intermediate substrate C:N, fungal N mineralisation fuelled bacterial growth, increasing total microbial biomass and decreasing net N mineralisation. Therefore, we conclude that differences in bacterial and fungal physiology may have large consequences for ecosystem-scale C and N cycling.