A numerical evaluation of chamber methodologies used in measuring the δ 13 C of soil respiration

Measurement of the δ 13 C value of soil‐respired CO 2 ( δ r ) has become a commonplace method through which ecosystem function and C dynamics can be better understood. Despite its proven utility there is currently no consensus on the most robust method with which to measure δ r . Static and dynamic chamber systems are both commonly used for this purpose; however, the literature on these methods provides evidence suggesting that measurements of δ r made with these chamber systems are neither repeatable (self‐consistent) nor comparable across methodologies. Here we use a three‐dimensional (3‐D) numerical soil‐atmosphere‐chamber model to test these chamber systems in a ‘surrogate reality’. Our simulations show that each chamber methodology is inherently biased and that no chamber methodology can accurately predict the true δ r signature under field conditions. If researchers intend to use δ r to study in situ ecosystem processes, the issues with these chamber systems need to be corrected either by using diffusive theory or by designing a new, unbiased δ r measurement system. Copyright © 2009 John Wiley & Sons, Ltd.