A global synthesis reveals more response sensitivity of soil carbon flux than pool to warming

Abstract

Climate change continues to garner attention in the public sphere. Most recognize its potential to affect global carbon (C) dynamics in the biosphere. Many posit that global warming promotes the decomposition of soil organic C (SOC) and increases soil C release. However, it remains unclear how soil C dynamics respond to different influencing factors (e.g., warming method, magnitude/duration, mean annual temperature (MAT) and precipitation (MAP)) across ecosystems on a global scale. Here, we performed a meta-analysis to identify the general global patterns of how warming impacts soil C dynamics. Across all terrestrial ecosystems, warming reduced SOC by 4.96% and stimulated soil microbial biomass C (MBC), soil respiration (SR), and heterotrophic respiration (HR) by 6.30, 14.56, and 8.42%, respectively. Warming affected soil C pools in grasslands and soil C fluxes in forests. The changes in SOC did not correlate to warming magnitude/duration or climate factors (MAT and MAP). However, changes in both MBC and SR did correlate to warming magnitude/duration and MAT. The changes in HR showed a quadratic response to warming magnitude and a linear response to MAP. Open-top chamber method can effectively affect soil C pools. SR proved to be more sensitive than HR to most warming methods. Our results showed that soil C release exhibited more sensitivity to warming magnitude/duration or MAT/MAP than did net soil C sequestration. These results indicate that warming induces accelerated transition of soils from C sink to C source. Furthermore, they show the potential for global warming effects to exacerbate the positive feedback loop in terrestrial ecosystems. However, the declining rates-of-change in SR and HR under high magnitude warming may mitigate the positive feedback. Our analyses can improve the predictions of feedback between atmospheric and soil C pools.