The source of microbial C has little impact on soil organic matter stabilisation in forest ecosystems

Abstract The source of microbial C is thought to impact its stability in soil due to variations in cellular biochemistry. It has been hypothesised that a fungal‐dominated community stabilises more C than a bacterial‐dominated community, in part due to chemical recalcitrance of their non‐living biomass, particularly cell wall components and pigments. We compared the turnover of 13 C‐labelled (99.9 atom %) temperate and tropical microbial isolates [i.e. fungi, Gram‐positive bacteria (including actinobacteria) and Gram‐negative bacteria] in temperate (California) and tropical (Puerto Rico) forest soils. While significant differences in 13 C recovery and mean residence times occurred among some microbial additions, similar turnover rates were observed, and in general, results do not support the view that microbial biochemistry affects soil C maintenance. Different effects by microbial necromass additions in California and Puerto Rico suggest that ecosystem‐specific effects may be as important to microbial C stabilisation as its macromolecular composition and recalcitrance.