Mineralization of (1,2-14C) acetic acid at 20°C in microcosms with Atacama soil samples. Each point represents the mean cumulative mineralization expressed as the cumulative % of radiolabel recovered as 14CO2 from triplicate assays including sterile controls (dashed lines). (a) Radiolabeled acetic acid (0.045 μCi) was added at the beginning of the experiment and (b) again at day 47 to the same microscosms. Black arrows: second addition of radiolabel substrate. Error bars are standard error of the mean.