Application of Combustion Module Coupled with Cavity Ring-Down Spectroscopy for Simultaneous Measurement of SOC and δ13C-SOC

Dan Liu,Junjie Lin,Zhiguo Yu

doi:10.1155/2018/6893454

Abstract

Quantifying the decomposition of soil organic carbon (SOC) fractions under climate change is essential to predict carbon-climate feedbacks. The accuracy and utility of a combustion module coupled with cavity ring-down spectroscopy (CM-CRDS) system were assessed for simultaneously determining SOC and δ13C-SOC. Using a range of standard materials as well as soil samples, we compared the results of the CM-CRDS system with those from other systems for determining C content and δ13C value. The CM-CRDS system can determine a vast range of δ13C values from −7.639‰ to −34.318‰. The δ13C values measured at C content > 0.2 mg C, corresponding to 1000 ppmv of CO2, were relatively stable. However, below a content of 0.2 mg C, the δ13C values appeared unsteady and seemed to be affected by background signal. We found that, with the increase of C content, the recovery rates (RRs) for soil samples also increased. On the contrary, the RRs for inorganic materials were much lower than organic material and soil samples. Overall, the CM-CRDS system provides a valid alternative method to determine SOC and δ13C-SOC for a sample simultaneously.

Highlights

Quantifying soil organic carbon (SOC) decomposition under climate change is essential to predict carbon-climate feedbacks and global C cycle [1, 2]
Previous studies have tested δ13C-SOC by elemental analyzer coupled with isotope ratio mass spectrometry (IRMS) [6], gas chromatography (GC) coupled with IRMS [6], or nuclear magnetic resonance (NMR) spectrometry [7]
We evaluated the linearity of the combustion module (CM)-CRDS method by plotting the measured 12CO2 concentration against the carbon content (0.15–1.07 mg C) of acetanilide standard (Figure 2)

Summary

Introduction

Quantifying soil organic carbon (SOC) decomposition under climate change is essential to predict carbon-climate feedbacks and global C cycle [1, 2]. The approaches for investigating SOC fraction decomposition include improved measurement systems and labeling experiments using carbon isotope tracers (13C or 14C). Few studies have reported the application of CM-CRDS system for simultaneous measurement of SOC and δ13C-SOC in soil samples. Combustion module (CM) coupled with CRDS system was explored as an alternative method for making bulk measurements of SOC and δ13C-SOC.

Results

Conclusion