Nitrogen addition to soil affects microbial carbon use efficiency: Meta‐analysis of similarities and differences in 13C and 18O approaches

摘要

Abstract The carbon use efficiency (CUE) of soil microorganisms is a critical parameter for the first step of organic carbon (C) transformation by and incorporation into microbial biomass and shapes C cycling in terrestrial ecosystems. As C and nitrogen (N) cycles interact closely and N availability affects microbial metabolism, N addition to soil may shift the microbial CUE. We conducted a meta‐analysis (100 data pairs) to generalize information about the microbial CUE response to N addition in soil based on the two most common CUE estimation approaches: (i) 13C‐labelled substrate addition (13C‐substrate) and (ii) 18O‐labelled water addition (18O‐H2O). The mean microbial CUE in soils across all biomes and approaches was 0.37. The effects of N addition on CUE, however, were depended on the approach: CUE decreased by 12 if measured by the 13C‐substrate approach, while CUE increased by 11 if measured by the 18O‐H2O approach. These differences in the microbial CUE response depending on the estimation approach are explained by the divergent reactions of microbial growth to N addition: N addition decreases the 13C incorporation into microbial biomass (this parameter is in the numerator by CUE calculation based on the 13C‐substrate approach). In contrast, N addition slightly increases (although statistically insignificant) the microbial growth rate (in the numerator of the CUE calculation when assessed by the 18O‐H2O approach), significantly raising the CUE. We explained these N addition effects based on CUE regulation mechanisms at the metabolic, cell, community, and ecosystem levels. Consequently, the differences in the microbial responses (microbial growth, respiration, C incorporation, community composition, and dormant or active states) between the 13C‐substrate and 18O‐H2O approaches need to be considered. Thus, these two CUE estimation approaches should be compared to understand microbially mediated C and nutrient dynamics under increasing anthropogenic N input and other global change effects.