Role of calcium in aggregate formation and soil organic matter stabilization in topsoils on calcareous and silicate parent material

Soil organic matter (SOM) in organic surface layers and mineral topsoil horizons of forest soils is an important constituent of the global C cycle. It is susceptible to losses and conversion into atmospheric CO2 by current global warming; yet, calcium (Ca) stabilizes SOM by complexation and/or formation of SOM-mineral associations and aggregates. The mechanisms involved in this process as well as the microspatial structure of the formed SOM-Ca-mineral associations and aggregates are unknown. We aim to reduce this knowledge deficit by conducting µ-XRF and Ca µ-XANES analyses on topsoil samples of dominating forest soil types on silicate and on calcareous bedrock at ID 21 of ESRF. Combined with existing information and results from NanoSIMS and 13C NMR studies conducted on the same samples, the results of our experiment will provide clues for sustainable SOM management under climate warming.