Ecosystem Carbon Fluxes Exhibit Thermal Response Thresholds at Which Carbon–Climate Feedback Changes

ABSTRACT Aim The carbon–climate feedback of terrestrial ecosystems plays a key role in determining atmospheric carbon dioxide concentrations. Ecosystem respiration (ER) has been demonstrated to be more sensitive than gross primary productivity (GPP) to increasing temperature, leading to positive carbon–climate feedback. However, the direction and magnitude of the feedback are unclear across diverse thermal regimes. The objective of this study was to assess the variability in the carbon–climate feedback with thermal regimes. Location Global. Time Period 1991–2014. Major Taxa Studied Terrestrial ecosystems. Methods We used linear and piecewise‐linear mixed‐effects models, quantified based on the Arrhenius function, to find the models that best characterise the temperature dependence of net ecosystem exchange (NEE), GPP and ER at global and climate scales. Results By analysing global data from 184 FLUXNET sites, we show that the temperature dependence of terrestrial carbon flux changes at two temperature threshold zones: −5.4°C to −1.7°C and 17.0°C to 17.1°C. The carbon–climate feedback is positive at cold and warm temperatures but negative at intermediate temperatures. This general pattern was observed in all but one of the five climatic zones. Main Conclusions Climate warming may not simply reduce the carbon uptake potential of terrestrial ecosystems, but the effects are dependent on ambient temperatures. Our findings highlight that temperature thresholds should be adequately considered for a more realistic presentation of carbon–climate feedback under future climate change.