Root exclusion through trenching does not affect the isotopic composition of soil CO2 efflux

Disentangling the autotrophic and heterotrophic components of soil CO₂ efflux is critical to understanding the role of soil system in terrestrial carbon (C) cycling. In this study, we combined a stable C-isotope natural abundance approach with the trenched plot method to determine if root exclusion significantly affected the isotopic composition (δ¹³C) of soil CO₂ efflux (R_S). This study was performed in different forest ecosystems: a tropical rainforest and two temperate broadleaved forests, where trenched plots had previously been installed. At each site, R_S and its δ¹³C (δ¹³C_Rs) tended to be lower in trenched plots than in control plots. Contrary to R_S, δ¹³C_Rs differences were not significant. This observation is consistent with the small differences in δ¹³C measured on organic matter from root, litter and soil. The lack of an effect on δ¹³C_Rs by root exclusion could be from the small difference in δ¹³C between autotrophic and heterotrophic soil respirations, but further investigations are needed because of potential artefacts associated with the root exclusion technique.