Articles | Volume 15, issue 4
Research article
20 Feb 2018
Research article |  | 20 Feb 2018

Stable isotopic constraints on global soil organic carbon turnover

Chao Wang, Benjamin Z. Houlton, Dongwei Liu, Jianfeng Hou, Weixin Cheng, and Edith Bai

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2 concentrations and global climate change. However, reliably measuring SOC turnover rates on large spatial and temporal scales remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ13C of vegetation and soil reported in the literature (176 separate soil profiles), to examine large-scale controls of climate, soil physical properties and nutrients over patterns of SOC turnover across terrestrial biomes worldwide. We report a significant relationship between β and calculated soil C turnover rates (k), which were estimated by dividing soil heterotrophic respiration rates by SOC pools. ln( − β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with mean annual precipitation, implying strong-feedbacks of SOC turnover to climate changes. Soil nitrogen (N) and clay content correlate strongly and positively with ln( − β), revealing the additional influence of nutrients and physical soil properties on SOC decomposition rates. Furthermore, a strong (R2 = 0.76; p < 0.001) linear relationship between ln( − β) and estimates of litter and root decomposition rates suggests similar controls over rates of organic matter decay among the generalized soil C stocks. Overall, these findings demonstrate the utility of soil δ13C for independently benchmarking global models of soil C turnover and thereby improving predictions of multiple global change influences over terrestrial C-climate feedback.

Short summary
Soil contains a large amount of organic carbon and plays a crucial role in regulating Earth's C cycle and climate system. In this study, we collected soil-carbon isotope data within a 1 m depth globally and provided an isotope-based approach for understanding soil carbon decomposition rate. Compared with other methods, utilization of C isotope composition ratios in the soil profile provides an independent approach that does not rely on disruption of plant-soil-microbe interactions.
Final-revised paper