[M-IS09] 生物地球化学

[MIS09-04] 森林土壌における溶存有機炭素溶脱と酸性化のフィードバックを駆動するメカニズム

*藤井 一至¹、早川 智恵²、ゼン ジンセン¹、舟川 晋也³、小崎 隆⁴ (1.森林総合研究所、2.宇都宮大学、3.京都大学、4.愛知大学)

キーワード：土壌、森林、溶存有機炭素

Whether stable organic matter in soils is derived mainly from plant recalcitrant litters or microbial necromass is a key but still controversial question to sequester soil C efficiently under changing climate. Leaching of dissolved organic carbon (DOC) from the thick organic layers is a major C source for mineral soil in temperate forests, but the validity at the global scale has not been testified due to the scarcity of available data from the Arctic and the tropics with thinner organic layers. By quantifying the DOC fluxes from the Arctic and the tropics, we found that DOC fluxes from the organic layers (32 to 836 kg C ha⁻¹ yr⁻¹) increased with annual precipitation at global scale, but not with organic layer C stock nor with C input from canopy (litterfall and throughfall DOC). The leached DOC from the organic layers per C input were variable (0.4 to 32.4 %), but DOC production increases with increasing soil acidity through the increased activities of lignin-degrading enzymes (manganese-dependent and lignin peroxidases) and their potential producers of white rot fungi. Leached DOC contributes to 0.6 to 55.0 % of C in the mineral soils with minimum amounts of short-range order minerals (> 0.5 %), while the remaining proportion attributing to root litter C inputs is mainly processed by microbes to be stabilized as microbial necromass etc. Positive feedback between DOC leaching and soil acidification leads to an increase in soil C storage at global scale except for volcanic soils, where specific-processes (burial of organic matter by volcanic deposition or char input by fires) are dominant. The leaching and sorption of DOC could be major pathway in acidic soils through feedback, while root litter input is a major C source in less acidic soils.