Sulfur isotopic signatures of water-soluble sulfate in needles of Pinus Massoniana Lamb in two Chinese areas

This study analyzed the water-soluble sulfate (S_SO4) and total sulfur (S_T) concentrations and their isotopic signatures (δ³⁴S_SO4 and δ³⁴S_T) in needles of Pinus massoniana Lamb collected from Guiyang (seriously affected by acid rain) and Yunnan areas (acid rain did not occur), China SW. The results indicated that the S_SO4 concentrations in needles of Pinus massoniana Lamb collected from several Chinese areas were found to be significantly correlated to ambient sulfur dioxide (R ² = 0.9176, p = 0.01), showing that S_SO4 concentrations in needles were more reliable to indicate atmospheric sulfur. The average δ³⁴S_SO4 (−7.2 ‰) and δ³⁴S_TS (−5.1 ‰) in needles in Guiyang areas were significantly lower than those in Yunnan areas (+3.9 and +5.7 ‰, respectively), which were in accordance with the lower δ³⁴S of coals in Guiyang areas than in Yunnan areas. The δ³⁴S_SO4 and δ³⁴S_TS in needles became less positive with a distance from a plant combusted ³⁴S-enriched coals while for another plant combusted ³⁴S-depleted coals, more positive was observed. These results indicated that δ³⁴S_SO4 in needles was also a good indicator of atmospheric sulfur sources. A very small difference between δ³⁴ S_T and δ³⁴ S_SO4 for most needle samples suggested that little isotopic fractionation accompanies sulfur assimilation processes.