A global meta-analysis of soil respiration in response to elevated CO2

Soil respiration (R_s) is a crucial component of the terrestrial ecosystem carbon (C) cycle, which significantly regulates atmospheric CO₂ concentrations. Although previous studies have suggested potential impacts of rising atmospheric CO₂ concentrations on R_s, most of these studies are limited in geographic distribution and variability in CO₂ exposure techniques. Globally, particularly across climatic conditions and vegetation types, resulting in the response of R_s to elevated CO₂ (eCO₂) remains poorly understood. In this study, 1191 paired observations from 207 published experimental eCO₂ studies were synthesized to quantify the response of R_s and its related factors to eCO₂. The results showed that eCO₂ significantly increased root biomass (32%), soil organic carbon (SOC, 3.6%), and soil water content (SWC, 9.6%), leading to an overall increase in R_s by 23%. Moreover, the impacts of eCO₂ on R_s varied significantly across climate conditions and vegetation types. The positive effects of eCO₂ on R_s in humid regions (26%) were higher than that in arid regions (14%), primarily due to differences in climatic conditions. Furthermore, eCO₂ increased R_s in forest ecosystems (28%) was higher than that in grassland ecosystems (15%). Additionally, R_s was positively correlated with the magnitude of eCO₂. However, the response of R_s to eCO₂ duration exhibited a convex relationship, indicating that the positive effect of CO₂ on R_s may diminish when extended experimental durations. Our findings suggest that the effects of eCO₂ on R_s will vary significantly across ecosystems and climate regions. In summary, our study provides a scientific basis for enhancing the accuracy of soil C cycling models and informing effective climate change policies.