Regulation of CO2 and N2O fluxes by coupled carbon and nitrogen availability

Abstract

Carbon (C) and nitrogen (N) interactions contribute to uncertainty in current biogeochemical models that aim to estimate greenhouse gas (GHG, including CO _2 and N _2 O) emissions from soil to atmosphere. In this study, we quantified CO _2 and N _2 O flux patterns and their relationship along with increasing C additions only, N additions only, a C gradient combined with excess N, and an N gradient with excess C via laboratory incubations. Conventional trends, where labile C or N addition results in higher CO _2 or N _2 O fluxes, were observed. However, at low levels of C availability, saturating N amendments reduced soil CO _2 flux while with high C availability N amendments enhanced it. At saturating C conditions increasing N amendments first reduced and then increased CO _2 fluxes. Similarly, N _2 O fluxes were initially reduced by adding labile C under N limited conditions, but additional C enhanced N _2 O fluxes by more than two orders of magnitude in the saturating N environment. Changes in C or N use efficiency could explain the altered gas flux patterns and imply a critical level in the interactions between N and C availability that regulate soil trace gas emissions and biogeochemical cycling. Compared to either N or C amendment alone, the interaction of N and C caused ∼60 and ∼5 times the total GHG emission, respectively. Our findings suggested that the response of CO _2 and N _2 O fluxes along stoichiometric gradients in C and N availability should be accounted for interpreting or modeling the biogeochemistry of GHG emissions.

Keywords

• CO2
• N2O
• carbon use efficiency (CUE)
• nitrogen use efficiency (NUE)
• greenhouse gases
• agricultural ecosystem