| Summary: | Ecosystems modulate the amount of carbon (C) that is stored and recycled. With increasing temperatures, especially in the Arctic, it is expected that more carbon will be respired than accumulated in soils. Typically, soil carbon losses are quantified by the amount of carbon dioxide (CO 2 ) that leaves the system. The proportion of microbial- vs. plant-respired CO 2 , together with the age of the microbially-decomposing C, can be assessed by determining the radiocarbon (14C) content of the respired CO 2 . Recently, a new method has been developed to study microbial C flows: compound specific 14C measurements of microbial lipids, phospholipid fatty acids (PLFA). Both approaches have been used to study environmental processes, but to date these two methods have not been compared directly on Arctic samples. Here, we collected active layer Arctic soil cores underlying shrub or graminoid tussock tundra (n=3/site). After a short pre-incubation to thaw the cores, subsectioned cores were incubated for up to one month. Post incubation, the quantity and 14C content of respired CO 2 and soil PLFAs were determined. From the litter layer to the deep mineral soils in both cores (n=16 samples), the isotopic composition of the CO 2 and PLFAs were the statistically identical even though the respired ∆14CO 2 ranged by more than 350‰. In addition, the magnitude of the respired CO 2 and PLFA quantity were correlated. However, soils from the different vegetation types had different rates of respiration and PLFA concentrations. This work shows that 14C measurements of both microbial respiration and PLFAs provide comparable results.
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