Abstract: In this study, we collected leaf litter from four main afforestation species (i.e., Liquidambar formosana, Schima superba, Pinus massoniana, and Pinus elliottii) in subtropical regions of Jiangxi Province. Litter was decomposed for 150 and 360 days in the air and on the ground. Then, we assessed the effects of decomposition position on the amount, C∶N∶P stoichiometry and ultraviolet-visible absorbance optical properties of litterderived dissolved organic matter (DOM) in subtropical plantations. After 150 days decomposition, L. formosana,P. massoniana, and P. elliottiilitter decomposed on the ground produced higher dissolved organic carbon (DOC) amounts than those in the air, whereas the pattern of S. superba litter was opposite. After 360 days of decomposition, the effect of decomposition position on litter-derived DOC production was species-specific. After 150 days of decomposition, C∶N, C∶P, and N∶P ratios were higher in the leachate of tree litter decomposed in the air than those on the ground. The effect of decomposition position on C∶N∶P stoichiometry was dependent on litter type after 360 days of decomposition. Litter of broad-leaved tree species (L. formosana and S. superba) decomposed in the air often had lower SUVA₂₅₄, SUVA₂₈₀, and SUVA₃₅₀ values (i.e., lower aromaticity of DOM), but higher S_275-295 and S_350-400 values (i.e., lower molecular weight) in the leachates than that on the ground after 150 and 360 days of decomposition. For coniferous trees (P. massoniana and P. elliotti), litter-derived DOM aromaticity and molecular weight were lower in the air than on the ground after 150 days of decomposition, but greater after 360 days of decomposition. These results suggest that decomposition position is an important factor determining the quantity and quality of litter-derived DOM in subtropical plantations, and such effect is regulated by tree species and the stage of decomposition.

Key words: aromatic degree, decomposition position, decomposition stage, stoichiometric characteristics, leaching.