Exciting Development: Real-Time Carbon Isotope Measurements for Quantifying Soil Carbon - A Strategic Asset in Combating Greenhouse Gas Emissions and Mitigating Climate Change

Measurements of δ 13C in soil organic matter and soil-respired δ 13C-CO2 are an important tool used to determine rates of processes and fates of carbon (C) compounds on a variety of scales and for understanding the C cycle in soils. In near-surface soils where diffusion is the dominant mechanism of gas transport, it must be recognized that these systems rarely in isotopic steady state. Simple changes, such as variation in respiration rate or infiltration of rainwater alter the soil gas diffusion regime and cause transient isotopic disequilibrium. These transient fractionations can persist for hours or days, and decay as the system approaches a new steady state. Stable isotopes are increasingly being used in understanding the early stages of fractionation in soil systems. However, there is a clear divergence between the true and measured isotopic signatures at the onset of this fractionation (Nickerson and Risk, 2009a). Further, the actual measurement methodologies themselves can affect the isotopic signatures being measured and so care must be taken in experimental design to avoid such effects (Nickerson and Risk, 2009b). The growing awareness of these effects, in tandem with new instrumentation for observing them in real time, has allowed better modeling and more accurate quantification of these soil gas processes (Phillips et al. in press; Subke et al. 2009)