Increased soil release of greenhouse gases shrinks terrestrial carbon uptake enhancement under warming.

Warming can accelerate the decomposition of soil organic matter and stimulate the release of soil greenhouse gases (GHGs), but to what extent soil release of methane (CH ₄ ) and nitrous oxide (N ₂ O) may contribute to soil C loss for driving climate change under warming remains unresolved. By synthesizing 1,845 measurements from 164 peer-reviewed publications, we show that around 1.5°C (1.16-2.01°C) of experimental warming significantly stimulates soil respiration by 12.9%, N ₂ O emissions by 35.2%, CH ₄ emissions by 23.4% from rice paddies, and by 37.5% from natural wetlands. Rising temperature increases CH ₄ uptake of upland soils by 13.8%. Warming-enhanced emission of soil CH ₄ and N ₂ O corresponds to an overall source strength of 1.19, 1.84, and 3.12 Pg CO ₂ -equivalent/year under 1°C, 1.5°C, and 2°C warming scenarios, respectively, interacting with soil C loss of 1.60 Pg CO ₂ /year in terms of contribution to climate change. The warming-induced rise in soil CH ₄ and N ₂ O emissions (1.84 Pg CO ₂ -equivalent/year) could reduce mitigation potential of terrestrial net ecosystem production by 8.3% (NEP, 22.25 Pg CO ₂ /year) under warming. Soil respiration and CH ₄ release are intensified following the mean warming threshold of 1.5°C scenario, as compared to soil CH ₄ uptake and N ₂ O release with a reduced and less positive response, respectively. Soil C loss increases to a larger extent under soil warming than under canopy air warming. Warming-raised emission of soil GHG increases with the intensity of temperature rise but decreases with the extension of experimental duration. This synthesis takes the lead to quantify the ecosystem C and N cycling in response to warming and advances our capacity to predict terrestrial feedback to climate change under projected warming scenarios.
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