Linking microbial carbon and nitrogen use to organic source stoichiometry and system-specific conditions

Soil microorganisms decompose a wide range of organic sources to meet their carbon (C) and energy needs. They further require nutrients such as nitrogen (N) in appropriate stoichiometric ratios to C. Organic sources are often N-poor (high C/N) compared to microbial biomass (low C/N). The extent of this stoichiometric imbalance influences organic matter decomposability, microbial C and N turnover, and ultimately C and N stabilization in soil.

Here, we investigate how organic source C/N and system-specific conditions impact the fate of C and N across diverse microbe-plant-soil systems. We synthesized data from 14 published isotope-tracing studies that applied ¹³C- and ¹⁵N-enriched organic sources and quantified the recovery of C and N from these sources in microbial biomass and bulk soil. The applied organic sources included microbial necromass and various plant residues spanning C/N ratios from 4 to 42. Similarly, the soils used in the studies were diverse, with bulk soil C/N ranging from 8 to 35 and pH values from 3 to 13.

The relative recovery of source N generally exceeds that of source C in microbial biomass and bulk soil, following the expected greater losses of C through microbial respiration. Moreover, low source C/N resulted in higher relative recoveries of source C and N in microbial biomass and bulk soil, likely reflecting more efficient microbial processing of sources with a stoichiometry that closely matches microbial needs. In addition, system-specific conditions, such as bulk soil C/N, influence the fate of C and N.

In our contribution, we aim to provide insights into the joint microbial use of C and N related to organic source stoichiometry and discuss how system-specific conditions and experimental design shape the observed patterns across diverse microbe-plant-soil systems.