Stable isotopic constraints on global soil organic carbon turnover

Abstract

Abstract. Carbon dioxide release during soil organic carbon (SOC) turnover is a pivotal component of atmospheric CO2concentrations and global climate change. However, reliably measuring SOC turnover rates at large spatial and temporal scales 10 remains challenging. Here we use a natural carbon isotope approach, defined as beta (β), which was quantified from the δ 13 C of vegetation and soil reported in the literature (182 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 by SOC pools. ln(-β) exhibits a significant linear relationship with mean annual temperature, but a more complex polynomial relationship with 15 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 (R 2 = 0.85; 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 δ 13 C for independently benchmarking global models of soil C turnover and thereby 20improving predictions of multiple global change influences over terrestrial C-climate feedback.

The spatial patterns of litter turnover time in Chinese terrestrial ecosystems

“…In our study, litter turnover time was rapid at low latitudes because of the spatial patterns of temperature and precipitation. This result was consistent with the results of other studies on litter decomposition (Portillo-Estrada et al, 2016;Wang et al, 2017;Zhang, Hui, Luo, & Zhou, 2008). Consistent with previous observations, the litter turnover time significantly decreased with the increases in MAT and MAP because of the dependence of microbial activity and respiration rates on temperature, which impacts soil moisture (Lellei-Kovács et al, 2016).…”

“…Litter dynamics is an important biogeochemical process that controls soil organic matter formation, nutrient release and energy cycling, affecting atmospheric CO 2 concentrations, plant growth and carbon sequestration. Consequently, understanding the litter turnover time is critical for quantifying the carbon footprints of the pedosphere, biosphere and atmosphere and for predicting global C dynamics (Wang et al, 2017). Moreover, litter turnover time is a critical parameter for ecosystem models (e.g., the CENTURY model, TECO model and Community Land Model) (Bonan, Hartman, Parton, & Wieder, 2013;Koven et al, 2013;Weng & Luo, 2008).…”

Including Stable Carbon Isotopes to Evaluate the Dynamics of Soil Carbon in the Land‐Surface Model ORCHIDEE

“…Turning to the second causal factor, because δ 13 C measurements can be used as an observational constraint for improving SOC turnover times (Acton et al, ; Luo et al, ; Wang et al, ) development and evaluation of the soil 13 C module in ORCHIDEE‐SOM may help, in the future, to better constrain the SOC turnover times and hence simulated SOC stocks at broad spatial and temporal scales (Balesdent et al, , ; Lawrence et al, ), whose output we discuss below.…”

Soil organic matter turnover depending on land use change: Coupling C/N ratios, δ13C, and lignin biomarkers

“…Empirical models showed a significant fit of linear regression between the logarithm of SOC content and its δ 13 C for most of the soils worldwide. The slope of the linear regression (defined as the β value) indicates a proxy for SOC turnover (e.g., Acton, Fox, Campbell, Rowe, & Wilkinson, 2013; Wang et al, 2018; Wang, Wei, et al, 2017; Zhao et al, 2019). In detail, Acton et al (2013) supported that a pronounced negative slope (the β value) is indicative for C isotopic fractionation during decomposition and physical mixing processes of SOC turnover across cold temperate to tropical forests.…”