Higher climate sensitivities weaken negative climate feedbacks of terrestrial ecosystem through carbon sequestration and nitrous oxide emissions

Terrestrial ecosystem acts as important carbon dioxide (CO₂) sinks and nitrous oxide (N₂O) sources. Ecosystem green-house-gas fluxes could further lead to a climate feedback, which are highly correlated with the C-N coupling. However, magnitudes of such composited feedbacks as well as contributions by individual ecological processes remained certain uncertainties. Here, we applied a terrestrial biosphere model QUINCY with fully C-N-coupling to comprehensively examine responses of CO₂ and N₂O fluxes to future climate changes and quantify contributions by individual processes. Our results showed that the trade-offs in CO₂ and N₂O still led a negative feedback (-3386.9 Tg CO₂ yr^-1) averaged over 2050-2100 under the SSP 5-8.5 scenario relative to SSP 1-2.6 scenario, however, which varies from -1761.7 Tg CO₂ yr^-1 to -5012.1 CO₂ yr^-1 with a high or low climate sensitivity to CO₂ increases.  Further process analysis showed that the CO₂ fertilization effects on ecosystem climate feedbacks were equivalent for high and low climate sensitivity, but the higher climate sensitivity led to less carbon sequestration on tropical plants as well as higher N₂O emissions. The climate feedbacks attributed to individual soil processes, including decomposition, nitrification, denitrification and nitrogen biological fixation, were also comprehensively quantified. This finding suggests that reducing the uncertainties in climate sensitivity estimates could be of great significance to better predict future terrestrial ecosystem green-house-gas fluxes as well as corresponding climate feedbacks.