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Ecosystem loss of soil inorganic carbon with agricultural conversion: fate, rate, mechanisms, and pathways

Final Report Summary - ELSIC (Ecosystem loss of soil inorganic carbon with agricultural conversion: fate, rate, mechanisms, and pathways)

Dr. Kim’s proposed research project was to explore how altered soil hydrology – by land use change or irrigation – can alter the dynamics of pedogenic carbonates. His proposed research followed on observations that there is an apparent loss of pedogenic carbonates in irrigated semi-arid lands. At MPI-BGC, Kim explored this process further by (1) measuring radiocarbon and stable isotope profiles of pedogenic carbonates in deep soil profiles of paired irrigated and non-irrigated lands, and (2) controlled incubation experiments designed to explore the kinetics of carbonate dissolution under conditions of different irrigation. The isotopic results demonstrated that there was no large increase in younger carbon transported downward in soil profiles in irrignated soils. The incubation experiments took a long time to set up an das a result some analyses are still underway. Hydrochemical modeling is also being perfomed, as the critical question in whether pedogenic carbonate dissolution causes a net impact on atmospheric CO2 depends on the source of Ca (weathering; i.e. new source, or reprecipitation of carbonates deeper in the same soil profile).

A second project initiated by Dr. Kim was to use radiocarbon to study the age of carbon in fine roots from a number of different plantation trees. This work follows up on work we have done at MPI-BGC showing that woody roots tend to be composed of carbon up to a decade old. More data from new tree types and climate/soil regimes are useful for explaining how this can be – i.e. whether C is old because roots have long lifespans, or because roots are grown from old C in storage reserves.