P_04

Estimating the age of carbon respired from terrestrial ecosystems using radiocarbon

Trumbore S¹, Sierra C¹, Hilman B¹, Hoyt A^1,2

¹Max Planck Society, Jena, Germany, ²Stanford University, Stanford, USA

Tracing radiocarbon through land ecosystems provides important information on the timescales of land C cycling.  The global ‘bomb’ radiocarbon tracer is particularly important for studying C sequestration and loss processes that can be altered by land management or climate change.

While many studies use radiocarbon to estimate the age of stored C, this talk will focus on estimating the age of carbon respired from ecosystems -  the transit time of ecosystem carbon.  In particular it will focus on the transit time distributions in different ecosystems with examples of  CO₂ respired by plants and soils.  The age of carbon respired from plants mixes very recently fixed photosynthetic products with C fixed years up to decades previously, depending on the ecosystem and the status of plant C balance.   The age of C respired from soils is mostly younger than the C age of bulk soil organic matter, and reflects the age of ‘labile’ or microbially accessible C fractions.  However, the age of respired C increases with soil depth, reinforcing the fact that C age is not a direct measure of decomposability.   Globally extrapolated transit times will provide an important constraint for C cycle models predicting dynamics into the next century. Data used in this presentation are from ISRaD, the international soil radiocarbon data base (www.soilradiocarbon.com), that is a community effort to provide an open platform for the ever-increasing data on radiocarbon in soils.   As the global capacity to measure radiocarbon increases, how we manage data has become a major challenge.