Application of eddy covariance measurements to the temperature dependence of soil organic matter mean residence time

The micrometeorological technique of eddy covariance is a powerful tool for characterizing the carbon (C) budget of terrestrial ecosystems. However, few attempts have been made to link canopy‐scale eddy exchange to soil C processes. Here we develop a simple means of using calculations derived from a global database of eddy flux measurements to examine the role of climate on soil C decomposition rates. We then compare the results of the eddy covariance calculations to the temperature dependence of soil C residence times determined by four common methods: laboratory incubations, direct soil respiration measurements, radiocarbon uptake, and stable C isotope change following land conversion. In all five methods, the soil organic C turnover time decreases exponentially with increasing mean annual temperature. The similar slopes and intercepts of the eddy flux and chamber measurements lend support for the robustness of micrometeorological techniques in measuring respiration. The similarities in the response of soil C turnover to temperature for the eddy flux and 14 C‐derived turnover times is especially encouraging in that bomb‐ 14 C measurements do not rely on any of the assumptions that were used to calculate soil C turnover from eddy flux data. However, the 13 C isotope method yields a significantly different slope and intercept than the other three techniques. The results of this work reinforce the recognized temperature dependence of soil C turnover and suggest that eddy flux experiments are a useful and additional approach for studying the soil C budget.