Temperate forests contain substantial carbon stocks that have potential feedbacks to global climate change. Whether temperate forests will mitigate or contribute to climate change is uncertain. For example, the dominant tree species composition in forests today is undergoing tremendous change, yet the impacts of these changes are almost completely unknown. We are investigating the influence of tree species on soil organic matter formation at a 35 year old common garden experiment in central Poland. Previous studies demonstrated significant differences among the 14 species on site with respect to plant traits such as litter production and chemistry. We sampled the mineral soil beneath 6 different tree species and analyzed the top 20 cm for total organic carbon content and radiocarbon abundance. Preliminary results indicate differences among species with respect to carbon storage in the mineral soil. Previous studies on-site indicate that litter calcium may drive differences in litter decomposition and % C in the forest floor; our results show that litter calcium may also be driving decadal scale soil carbon storage in the mineral horizon.