Effects of geological conditions and atmospheric deposition on soil biogeochemical properties in Japanese forested ecosystems revealed by Sr isotope analysis

The radiogenic strontium (Sr) isotope ratio ( 87 Sr/ 86 Sr) is a valuable tracer of cation dynamics in ecosystems, and has been used as a proxy for geological conditions and atmospheric deposition. In this study, 87 Sr/ 86 Sr was measured in litter and soil collected from 42 forest ecosystems in Japan to assess the effects of various environmental factors, such as geological conditions and atmospheric deposition, on soil biogeochemical properties. 87 Sr/ 86 Sr in organically bound Sr in the litter was higher at sites with soil parent materials of clastic rocks and chert whose geological age was older than that of the sites with igneous rocks, whose geological age was relatively young. In addition, 87 Sr/ 86 Sr in organically bound Sr in litter was higher at sites near the Sea of Japan due to the sea salt and transboundary eolian dust with silicate minerals originating from the Chinese desert via the winter monsoon. Path modeling analysis revealed that geology and atmospheric deposition were significant explanatory variables for the geographical distribution of litter and soil 87 Sr/ 86 Sr. A second path modeling analysis incorporating an existing dataset obtained in a previous study revealed an indirect and significant association of geological conditions and atmospheric deposition with soil acidity and base cation concentration through litter and soil 87 Sr/ 86 Sr. Consequently, soil acidification and mineral properties in Japanese forest ecosystems are indirectly affected by parent material weathering and atmospheric deposition, including long-range transboundary atmospheric deposition, as indicated by litter and soil 87 Sr/ 86 Sr.